Remove extra new lines

This uses a git dependency on Hyper for now.

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        rust_version: ['1.43.0', 'stable', 'nightly']
+        rust_version: ['1.46.0', 'stable', 'nightly']
         os: [ubuntu-latest, windows-latest, macOS-latest]
     steps:
     - uses: actions/checkout@v1
@@ -35,6 +35,23 @@ jobs:
           override: true
     - name: Run Tests
       run: cargo test
+  docs:
+    runs-on: ubuntu-latest
+    env:
+      RUSTDOCFLAGS: -Dwarnings
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install Rust Nightly
+      uses: actions-rs/toolchain@v1
+      with:
+          toolchain: nightly
+          override: true
+          components: rust-docs
+    - name: Check docs
+      uses: actions-rs/cargo@v1
+      with:
+        command: doc
+        args: --workspace --no-deps
   bench:
     name: Bench ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
@@ -49,4 +66,7 @@ jobs:
           toolchain: 'stable'
           override: true
     - name: Run Benchmarks
-      run: cargo bench
+      uses: actions-rs/cargo@v1
+      with:
+        command: bench
+        args: --all-features

COPYRIGHT

@@ -1,102 +1,94 @@
 Short version for non-lawyers:
 
-metrics is MIT licensed.
+`metrics` is MIT licensed.
 
 Longer version:
 
-Copyrights in the metrics project are retained by their contributors. No
+Copyrights in the `metrics` project are retained by their contributors. No copyright assignment is
-copyright assignment is required to contribute to the metrics project.
+required to contribute to the `metrics` project.
 
-Some files include explicit copyright notices and/or license notices.
+Some files include explicit copyright notices and/or license notices.  For full authorship
-For full authorship information, see the version control history.
+information, see the version control history.
 
-Except as otherwise noted (below and/or in individual files), metrics
+Except as otherwise noted (below and/or in individual files), `metrics` is licensed under the MIT
-is licensed under the MIT license <LICENSE> or
+license <LICENSE> or <http://opensource.org/licenses/MIT>.
-<http://opensource.org/licenses/MIT>.
 
 
-metrics includes packages written by third parties.
+`metrics` includes packages written by third parties.  The following third party packages are
-The following third party packages are included, and carry
+included, and carry their own copyright notices and license terms:
-their own copyright notices and license terms:
 
-* Portions of the API design are derived from tic
+* Portions of the API design are derived from the `tic` crate which carries the following license:
-  <https://github.com/brayniac/tic>, which carries the following
-  license:
 
     Copyright (c) 2016 Brian Martin
 
-    Permission is hereby granted, free of charge, to any person
+    Permission is hereby granted, free of charge, to any person obtaining a copy of this software
-    obtaining a copy of this software and associated documentation
+    and associated documentation files (the "Software"), to deal in the Software without
-    files (the "Software"), to deal in the Software without restriction,
+    restriction, including without limitation the rights to use, copy, modify, merge, publish,
-    including without limitation the rights to use, copy, modify, merge,
+    distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
-    publish, distribute, sublicense, and/or sell copies of the Software,
+    Software is furnished to do so, subject to the following conditions:
-    and to permit persons to whom the Software is furnished to do so,
-    subject to the following conditions:
 
-    The above copyright notice and this permission notice shall be
+    The above copyright notice and this permission notice shall be included in all copies or
-    included in all copies or substantial portions of the Software.
+    substantial portions of the Software.
 
-    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
-    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+    BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
-    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+    DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-    BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-    ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
-    CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-    SOFTWARE.
 
-* metrics is a fork of rust-lang-nursery/log which carries the following
+* metrics is a fork of `rust-lang-nursery/log` which carries the following license:
-  license:
 
     Copyright (c) 2014 The Rust Project Developers
 
-    Permission is hereby granted, free of charge, to any
+    Permission is hereby granted, free of charge, to any person obtaining a copy of this software
-    person obtaining a copy of this software and associated
+    and associated documentation files (the "Software"), to deal in the Software without
-    documentation files (the "Software"), to deal in the
+    restriction, including without limitation the rights to use, copy, modify, merge, publish,
-    Software without restriction, including without
+    distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
-    limitation the rights to use, copy, modify, merge,
+    Software is furnished to do so, subject to the following conditions:
-    publish, distribute, sublicense, and/or sell copies of
-    the Software, and to permit persons to whom the Software
-    is furnished to do so, subject to the following
-    conditions:
 
-    The above copyright notice and this permission notice
+    The above copyright notice and this permission notice shall be included in all copies or
-    shall be included in all copies or substantial portions
+    substantial portions of the Software.
-    of the Software.
 
-    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
-    ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+    BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-    TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
-    PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+    DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-    SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
-    OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
-    IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
-    DEALINGS IN THE SOFTWARE.
 
-* metrics-observer reuses code from `std::time::Duration` which carries
+* metrics-observer reuses code from `std::time::Duration` which carries the following license:
-  the following license:
 
-    Permission is hereby granted, free of charge, to any
+    Permission is hereby granted, free of charge, to any person obtaining a copy of this software
-    person obtaining a copy of this software and associated
+    and associated documentation files (the "Software"), to deal in the Software without
-    documentation files (the "Software"), to deal in the
+    restriction, including without limitation the rights to use, copy, modify, merge, publish,
-    Software without restriction, including without
+    distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
-    limitation the rights to use, copy, modify, merge,
+    Software is furnished to do so, subject to the following conditions:
-    publish, distribute, sublicense, and/or sell copies of
-    the Software, and to permit persons to whom the Software
-    is furnished to do so, subject to the following
-    conditions:
 
-    The above copyright notice and this permission notice
+    The above copyright notice and this permission notice shall be included in all copies or
-    shall be included in all copies or substantial portions
+    substantial portions of the Software.
-    of the Software.
 
-    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
-    ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+    BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
-    TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
-    PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+    DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-    SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
-    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+
-    OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+  * metrics includes code from the `beef` crate which carries the following license:
-    IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+
-    DEALINGS IN THE SOFTWARE.
+    Copyright (c) 2020 Maciej Hirsz <hello@maciej.codes>
+
+    The MIT License (MIT)
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy of this software
+    and associated documentation files (the "Software"), to deal in the Software without
+    restriction, including without limitation the rights to use, copy, modify, merge, publish,
+    distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in all copies or
+    substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
+    BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+    DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Cargo.toml

@@ -9,3 +9,7 @@ members = [
   "metrics-tracing-context",
 ]
 exclude = ["metrics-observer"]
+
+[patch.crates-io]
+hyper = { git = "https://github.com/hyperium/hyper/", rev = "ed2b22a7f66899d338691552fbcb6c0f2f4e06b9" }
+

metrics-benchmark/src/main.rs

@@ -80,7 +80,7 @@ impl Generator {
 impl Drop for Generator {
     fn drop(&mut self) {
         info!(
-            "    sender latency: min: {:9} p50: {:9} p95: {:9} p99: {:9} p999: {:9} max: {:9}",
+            "    sender latency: min: {:8} p50: {:8} p95: {:8} p99: {:8} p999: {:8} max: {:8}",
             nanos_to_readable(self.hist.min()),
             nanos_to_readable(self.hist.value_at_percentile(50.0)),
             nanos_to_readable(self.hist.value_at_percentile(95.0)),
@@ -196,7 +196,7 @@ fn main() {
     info!("--------------------------------------------------------------------------------");
     info!(" ingested samples total: {}", total);
     info!(
-        "snapshot retrieval: min: {:9} p50: {:9} p95: {:9} p99: {:9} p999: {:9} max: {:9}",
+        "snapshot retrieval: min: {:8} p50: {:8} p95: {:8} p99: {:8} p999: {:8} max: {:8}",
         nanos_to_readable(snapshot_hist.min()),
         nanos_to_readable(snapshot_hist.value_at_percentile(50.0)),
         nanos_to_readable(snapshot_hist.value_at_percentile(95.0)),

metrics-exporter-prometheus/Cargo.toml

@@ -27,8 +27,8 @@ parking_lot = "0.11"
 thiserror = "1.0"
 
 # Optional
-hyper = { version = "0.13", default-features = false, features = ["tcp"], optional = true }
+hyper = { version = "0.14.0-dev", default-features = false, features = ["tcp", "server", "http1", "http2"], optional = true }
-tokio = { version = "0.2", features = ["rt-core", "tcp", "time", "macros"], optional = true }
+tokio = { version = "0.3", features = ["rt", "net", "time", "macros"], optional = true }
 
 [dev-dependencies]
 quanta = "0.6"

metrics-exporter-prometheus/src/lib.rs

@@ -13,13 +13,14 @@ use metrics_util::{
     parse_quantiles, CompositeKey, Handle, Histogram, MetricKind, Quantile, Registry,
 };
 use parking_lot::RwLock;
+use std::collections::HashMap;
 use std::io;
 use std::iter::FromIterator;
 use std::net::{IpAddr, Ipv4Addr, SocketAddr};
 use std::sync::Arc;
 #[cfg(feature = "tokio-exporter")]
 use std::thread;
-use std::{collections::HashMap, time::SystemTime};
+use std::time::SystemTime;
 use thiserror::Error as ThisError;
 #[cfg(feature = "tokio-exporter")]
 use tokio::{pin, runtime, select};
@@ -211,7 +212,6 @@ impl Inner {
                 output.push_str(value.to_string().as_str());
                 output.push_str("\n");
             }
-            output.push_str("\n");
         }
 
         for (name, mut by_labels) in gauges.drain() {
@@ -233,7 +233,6 @@ impl Inner {
                 output.push_str(value.to_string().as_str());
                 output.push_str("\n");
             }
-            output.push_str("\n");
         }
 
         let mut sorted_overrides = self
@@ -316,8 +315,6 @@ impl Inner {
                 output.push_str(count.to_string().as_str());
                 output.push_str("\n");
             }
-
-            output.push_str("\n");
         }
 
         output
@@ -345,7 +342,7 @@ impl PrometheusRecorder {
     fn add_description_if_missing(&self, key: &Key, description: Option<&'static str>) {
         if let Some(description) = description {
             let mut descriptions = self.inner.descriptions.write();
-            if !descriptions.contains_key(key.name().as_ref()) {
+            if !descriptions.contains_key(key.name().to_string().as_str()) {
                 descriptions.insert(key.name().to_string(), description);
             }
         }
@@ -443,14 +440,16 @@ impl PrometheusBuilder {
     /// installing the recorder as the global recorder.
     #[cfg(feature = "tokio-exporter")]
     pub fn install(self) -> Result<(), Error> {
-        let (recorder, exporter) = self.build_with_exporter()?;
+        let runtime = runtime::Builder::new_current_thread()
-        metrics::set_boxed_recorder(Box::new(recorder))?;
-
-        let mut runtime = runtime::Builder::new()
-            .basic_scheduler()
             .enable_all()
             .build()?;
 
+        let (recorder, exporter) = {
+            let _guard = runtime.enter();
+            self.build_with_exporter()
+        }?;
+        metrics::set_boxed_recorder(Box::new(recorder))?;
+
         thread::Builder::new()
             .name("metrics-exporter-prometheus-http".to_string())
             .spawn(move || {
@@ -596,7 +595,11 @@ fn key_to_parts(key: Key) -> (String, Vec<String>) {
     let name = key.name();
     let labels = key.labels();
     let sanitize = |c| c == '.' || c == '=' || c == '{' || c == '}' || c == '+' || c == '-';
-    let name = name.replace(sanitize, "_");
+    let name = name
+        .parts()
+        .map(|s| s.replace(sanitize, "_"))
+        .collect::<Vec<_>>()
+        .join("_");
     let labels = labels
         .into_iter()
         .map(|label| {

metrics-macros/src/lib.rs

@@ -224,13 +224,13 @@ pub fn histogram(input: TokenStream) -> TokenStream {
 
 fn get_expanded_registration(
     metric_type: &str,
-    key: LitStr,
+    name: LitStr,
     unit: Option<Expr>,
     description: Option<LitStr>,
     labels: Option<Labels>,
 ) -> proc_macro2::TokenStream {
     let register_ident = format_ident!("register_{}", metric_type);
-    let key = key_to_quoted(key, labels);
+    let key = key_to_quoted(labels);
 
     let unit = match unit {
         Some(e) => quote! { Some(#e) },
@@ -244,6 +244,7 @@ fn get_expanded_registration(
 
     quote! {
         {
+            static METRIC_NAME: [metrics::SharedString; 1] = [metrics::SharedString::const_str(#name)];
             // Only do this work if there's a recorder installed.
             if let Some(recorder) = metrics::try_recorder() {
                 // Registrations are fairly rare, don't attempt to cache here
@@ -257,7 +258,7 @@ fn get_expanded_registration(
 fn get_expanded_callsite<V>(
     metric_type: &str,
     op_type: &str,
-    key: LitStr,
+    name: LitStr,
     labels: Option<Labels>,
     op_values: V,
 ) -> proc_macro2::TokenStream
@@ -288,15 +289,17 @@ where
                 let labels_len = quote! { #labels_len };
 
                 quote! {
+                    static METRIC_NAME: [metrics::SharedString; 1] = [metrics::SharedString::const_str(#name)];
                     static METRIC_LABELS: [metrics::Label; #labels_len] = [#(#labels),*];
                     static METRIC_KEY: metrics::KeyData =
-                        metrics::KeyData::from_static_parts(#key, &METRIC_LABELS);
+                        metrics::KeyData::from_static_parts(&METRIC_NAME, &METRIC_LABELS);
                 }
             }
             None => {
                 quote! {
+                    static METRIC_NAME: [metrics::SharedString; 1] = [metrics::SharedString::const_str(#name)];
                     static METRIC_KEY: metrics::KeyData =
-                        metrics::KeyData::from_static_name(#key);
+                        metrics::KeyData::from_static_name(&METRIC_NAME);
                 }
             }
             _ => unreachable!("use_fast_path == true, but found expression-based labels"),
@@ -314,9 +317,11 @@ where
         }
     } else {
         // We're on the slow path, so we allocate, womp.
-        let key = key_to_quoted(key, labels);
+        let key = key_to_quoted(labels);
         quote! {
             {
+                static METRIC_NAME: [metrics::SharedString; 1] = [metrics::SharedString::const_str(#name)];
+
                 // Only do this work if there's a recorder installed.
                 if let Some(recorder) = metrics::try_recorder() {
                     recorder.#op_ident(metrics::Key::Owned(#key), #op_values);
@@ -353,17 +358,19 @@ fn read_key(input: &mut ParseStream) -> Result<LitStr> {
     Ok(key)
 }
 
-fn key_to_quoted(name: LitStr, labels: Option<Labels>) -> proc_macro2::TokenStream {
+fn key_to_quoted(labels: Option<Labels>) -> proc_macro2::TokenStream {
     match labels {
-        None => quote! { metrics::KeyData::from_name(#name) },
+        None => quote! { metrics::KeyData::from_static_name(&METRIC_NAME) },
         Some(labels) => match labels {
             Labels::Inline(pairs) => {
                 let labels = pairs
                     .into_iter()
                     .map(|(key, val)| quote! { metrics::Label::new(#key, #val) });
-                quote! { metrics::KeyData::from_parts(#name, vec![#(#labels),*]) }
+                quote! {
+                    metrics::KeyData::from_parts(&METRIC_NAME[..], vec![#(#labels),*])
                 }
-            Labels::Existing(e) => quote! { metrics::KeyData::from_parts(#name, #e) },
+            }
+            Labels::Existing(e) => quote! { metrics::KeyData::from_parts(&METRIC_NAME[..], #e) },
         },
     }
 }

metrics-macros/src/tests.rs

@@ -10,9 +10,11 @@ fn test_get_expanded_registration() {
         get_expanded_registration("mytype", parse_quote! { "mykeyname" }, None, None, None);
 
     let expected = concat!(
-        "{ if let Some (recorder) = metrics :: try_recorder () { ",
+        "{ ",
+        "static METRIC_NAME : [metrics :: SharedString ; 1] = [metrics :: SharedString :: const_str (\"mykeyname\")] ; ",
+        "if let Some (recorder) = metrics :: try_recorder () { ",
         "recorder . register_mytype (",
-        "metrics :: Key :: Owned (metrics :: KeyData :: from_name (\"mykeyname\")) , ",
+        "metrics :: Key :: Owned (metrics :: KeyData :: from_static_name (& METRIC_NAME)) , ",
         "None , ",
         "None",
         ") ; ",
@@ -35,9 +37,11 @@ fn test_get_expanded_registration_with_unit() {
     );
 
     let expected = concat!(
-        "{ if let Some (recorder) = metrics :: try_recorder () { ",
+        "{ ",
+        "static METRIC_NAME : [metrics :: SharedString ; 1] = [metrics :: SharedString :: const_str (\"mykeyname\")] ; ",
+        "if let Some (recorder) = metrics :: try_recorder () { ",
         "recorder . register_mytype (",
-        "metrics :: Key :: Owned (metrics :: KeyData :: from_name (\"mykeyname\")) , ",
+        "metrics :: Key :: Owned (metrics :: KeyData :: from_static_name (& METRIC_NAME)) , ",
         "Some (metrics :: Unit :: Nanoseconds) , ",
         "None",
         ") ; ",
@@ -59,9 +63,11 @@ fn test_get_expanded_registration_with_description() {
     );
 
     let expected = concat!(
-        "{ if let Some (recorder) = metrics :: try_recorder () { ",
+        "{ ",
+        "static METRIC_NAME : [metrics :: SharedString ; 1] = [metrics :: SharedString :: const_str (\"mykeyname\")] ; ",
+        "if let Some (recorder) = metrics :: try_recorder () { ",
         "recorder . register_mytype (",
-        "metrics :: Key :: Owned (metrics :: KeyData :: from_name (\"mykeyname\")) , ",
+        "metrics :: Key :: Owned (metrics :: KeyData :: from_static_name (& METRIC_NAME)) , ",
         "None , ",
         "Some (\"flerkin\")",
         ") ; ",
@@ -84,9 +90,11 @@ fn test_get_expanded_registration_with_unit_and_description() {
     );
 
     let expected = concat!(
-        "{ if let Some (recorder) = metrics :: try_recorder () { ",
+        "{ ",
+        "static METRIC_NAME : [metrics :: SharedString ; 1] = [metrics :: SharedString :: const_str (\"mykeyname\")] ; ",
+        "if let Some (recorder) = metrics :: try_recorder () { ",
         "recorder . register_mytype (",
-        "metrics :: Key :: Owned (metrics :: KeyData :: from_name (\"mykeyname\")) , ",
+        "metrics :: Key :: Owned (metrics :: KeyData :: from_static_name (& METRIC_NAME)) , ",
         "Some (metrics :: Unit :: Nanoseconds) , ",
         "Some (\"flerkin\")",
         ") ; ",
@@ -108,7 +116,8 @@ fn test_get_expanded_callsite_fast_path_no_labels() {
 
     let expected = concat!(
         "{ ",
-        "static METRIC_KEY : metrics :: KeyData = metrics :: KeyData :: from_static_name (\"mykeyname\") ; ",
+        "static METRIC_NAME : [metrics :: SharedString ; 1] = [metrics :: SharedString :: const_str (\"mykeyname\")] ; ",
+        "static METRIC_KEY : metrics :: KeyData = metrics :: KeyData :: from_static_name (& METRIC_NAME) ; ",
         "if let Some (recorder) = metrics :: try_recorder () { ",
         "recorder . myop_mytype (metrics :: Key :: Borrowed (& METRIC_KEY) , 1) ; ",
         "} }",
@@ -130,8 +139,9 @@ fn test_get_expanded_callsite_fast_path_static_labels() {
 
     let expected = concat!(
         "{ ",
+        "static METRIC_NAME : [metrics :: SharedString ; 1] = [metrics :: SharedString :: const_str (\"mykeyname\")] ; ",
         "static METRIC_LABELS : [metrics :: Label ; 1usize] = [metrics :: Label :: from_static_parts (\"key1\" , \"value1\")] ; ",
-        "static METRIC_KEY : metrics :: KeyData = metrics :: KeyData :: from_static_parts (\"mykeyname\" , & METRIC_LABELS) ; ",
+        "static METRIC_KEY : metrics :: KeyData = metrics :: KeyData :: from_static_parts (& METRIC_NAME , & METRIC_LABELS) ; ",
         "if let Some (recorder) = metrics :: try_recorder () { ",
         "recorder . myop_mytype (metrics :: Key :: Borrowed (& METRIC_KEY) , 1) ; ",
         "} ",
@@ -154,9 +164,10 @@ fn test_get_expanded_callsite_fast_path_dynamic_labels() {
 
     let expected = concat!(
         "{ ",
+        "static METRIC_NAME : [metrics :: SharedString ; 1] = [metrics :: SharedString :: const_str (\"mykeyname\")] ; ",
         "if let Some (recorder) = metrics :: try_recorder () { ",
         "recorder . myop_mytype (metrics :: Key :: Owned (",
-        "metrics :: KeyData :: from_parts (\"mykeyname\" , vec ! [metrics :: Label :: new (\"key1\" , & value1)])",
+        "metrics :: KeyData :: from_parts (& METRIC_NAME [..] , vec ! [metrics :: Label :: new (\"key1\" , & value1)])",
         ") , 1) ; ",
         "} ",
         "}",
@@ -178,9 +189,10 @@ fn test_get_expanded_callsite_regular_path() {
 
     let expected = concat!(
         "{ ",
+        "static METRIC_NAME : [metrics :: SharedString ; 1] = [metrics :: SharedString :: const_str (\"mykeyname\")] ; ",
         "if let Some (recorder) = metrics :: try_recorder () { ",
         "recorder . myop_mytype (",
-        "metrics :: Key :: Owned (metrics :: KeyData :: from_parts (\"mykeyname\" , mylabels)) , ",
+        "metrics :: Key :: Owned (metrics :: KeyData :: from_parts (& METRIC_NAME [..] , mylabels)) , ",
         "1",
         ") ; ",
         "} }",
@@ -191,18 +203,17 @@ fn test_get_expanded_callsite_regular_path() {
 
 #[test]
 fn test_key_to_quoted_no_labels() {
-    let stream = key_to_quoted(parse_quote! {"mykeyname"}, None);
+    let stream = key_to_quoted(None);
-    let expected = "metrics :: KeyData :: from_name (\"mykeyname\")";
+    let expected = "metrics :: KeyData :: from_static_name (& METRIC_NAME)";
     assert_eq!(stream.to_string(), expected);
 }
 
 #[test]
 fn test_key_to_quoted_existing_labels() {
-    let stream = key_to_quoted(
+    let stream = key_to_quoted(Some(Labels::Existing(Expr::Path(
-        parse_quote! {"mykeyname"},
+        parse_quote! { mylabels },
-        Some(Labels::Existing(Expr::Path(parse_quote! { mylabels }))),
+    ))));
-    );
+    let expected = "metrics :: KeyData :: from_parts (& METRIC_NAME [..] , mylabels)";
-    let expected = "metrics :: KeyData :: from_parts (\"mykeyname\" , mylabels)";
     assert_eq!(stream.to_string(), expected);
 }
 
@@ -210,15 +221,12 @@ fn test_key_to_quoted_existing_labels() {
 /// Key).
 #[test]
 fn test_key_to_quoted_inline_labels() {
-    let stream = key_to_quoted(
+    let stream = key_to_quoted(Some(Labels::Inline(vec![
-        parse_quote! {"mykeyname"},
-        Some(Labels::Inline(vec![
         (parse_quote! {"mylabel1"}, parse_quote! { mylabel1 }),
         (parse_quote! {"mylabel2"}, parse_quote! { "mylabel2" }),
-        ])),
+    ])));
-    );
     let expected = concat!(
-        "metrics :: KeyData :: from_parts (\"mykeyname\" , vec ! [",
+        "metrics :: KeyData :: from_parts (& METRIC_NAME [..] , vec ! [",
         "metrics :: Label :: new (\"mylabel1\" , mylabel1) , ",
         "metrics :: Label :: new (\"mylabel2\" , \"mylabel2\")",
         "])"
@@ -228,10 +236,7 @@ fn test_key_to_quoted_inline_labels() {
 
 #[test]
 fn test_key_to_quoted_inline_labels_empty() {
-    let stream = key_to_quoted(parse_quote! {"mykeyname"}, Some(Labels::Inline(vec![])));
+    let stream = key_to_quoted(Some(Labels::Inline(vec![])));
-    let expected = concat!(
+    let expected = concat!("metrics :: KeyData :: from_parts (& METRIC_NAME [..] , vec ! [])");
-        "metrics :: KeyData :: from_parts (\"mykeyname\" , vec ! [",
-        "])"
-    );
     assert_eq!(stream.to_string(), expected);
 }

metrics-tracing-context/benches/layer.rs

@@ -1,5 +1,5 @@
 use criterion::{criterion_group, criterion_main, Benchmark, Criterion};
-use metrics::{Key, KeyData, Label, NoopRecorder, Recorder};
+use metrics::{Key, KeyData, Label, NoopRecorder, Recorder, SharedString};
 use metrics_tracing_context::{MetricsLayer, TracingContextLayer};
 use metrics_util::layers::Layer;
 use tracing::{
@@ -22,8 +22,9 @@ fn layer_benchmark(c: &mut Criterion) {
 
                 let tracing_layer = TracingContextLayer::all();
                 let recorder = tracing_layer.layer(NoopRecorder);
-                static LABELS: [Label; 1] = [Label::from_static_parts("foo", "bar")];
+                static KEY_NAME: [SharedString; 1] = [SharedString::const_str("key")];
-                static KEY_DATA: KeyData = KeyData::from_static_parts("key", &LABELS);
+                static KEY_LABELS: [Label; 1] = [Label::from_static_parts("foo", "bar")];
+                static KEY_DATA: KeyData = KeyData::from_static_parts(&KEY_NAME, &KEY_LABELS);
 
                 b.iter(|| {
                     recorder.increment_counter(Key::Borrowed(&KEY_DATA), 1);
@@ -32,8 +33,9 @@ fn layer_benchmark(c: &mut Criterion) {
         })
         .with_function("noop recorder overhead (increment_counter)", |b| {
             let recorder = NoopRecorder;
-            static LABELS: [Label; 1] = [Label::from_static_parts("foo", "bar")];
+            static KEY_NAME: [SharedString; 1] = [SharedString::const_str("key")];
-            static KEY_DATA: KeyData = KeyData::from_static_parts("key", &LABELS);
+            static KEY_LABELS: [Label; 1] = [Label::from_static_parts("foo", "bar")];
+            static KEY_DATA: KeyData = KeyData::from_static_parts(&KEY_NAME, &KEY_LABELS);
 
             b.iter(|| {
                 recorder.increment_counter(Key::Borrowed(&KEY_DATA), 1);

metrics-tracing-context/src/lib.rs

@@ -101,7 +101,7 @@ where
     }
 }
 
-/// [`TracingContext`] is a [`metrics::Recorder`] that injects labels from [`tracing::Span`]s.
+/// [`TracingContext`] is a [`metrics::Recorder`] that injects labels from[`tracing::Span`]s.
 pub struct TracingContext<R, F> {
     inner: R,
     label_filter: F,

metrics-tracing-context/src/tracing_integration.rs

@@ -20,7 +20,7 @@ impl Visit for Labels {
     }
 
     fn record_bool(&mut self, field: &Field, value: bool) {
-        let label = Label::new(field.name(), if value { "true" } else { "false" });
+        let label = Label::from_static_parts(field.name(), if value { "true" } else { "false" });
         self.0.push(label);
     }
 

metrics-util/Cargo.toml

@@ -26,11 +26,19 @@ harness = false
 name = "registry"
 harness = false
 
+[[bench]]
+name = "prefix"
+harness = false
+
+[[bench]]
+name = "filter"
+harness = false
+
 [dependencies]
 metrics = { version = "0.13.0-alpha.1", path = "../metrics", features = ["std"] }
 crossbeam-epoch = { version = "0.9", optional = true }
 crossbeam-utils = { version = "0.8", default-features = false }
-arc-swap = { version = "0.4", optional = true }
+arc-swap = { version = "1.0", optional = true }
 atomic-shim = { version = "0.1", optional = true }
 aho-corasick = { version = "0.7", optional = true }
 dashmap = { version = "3", optional = true }

metrics-util/benches/filter.rs

@@ -0,0 +1,61 @@
+use criterion::{criterion_group, criterion_main, Benchmark, Criterion};
+use metrics::{Key, KeyData, Label, NoopRecorder, Recorder, SharedString};
+use metrics_util::layers::{FilterLayer, Layer};
+
+fn layer_benchmark(c: &mut Criterion) {
+    c.bench(
+        "filter",
+        Benchmark::new("match", |b| {
+            let patterns = vec!["tokio"];
+            let filter_layer = FilterLayer::from_patterns(patterns);
+            let recorder = filter_layer.layer(NoopRecorder);
+            static KEY_NAME: [SharedString; 1] = [SharedString::const_str("tokio.foo")];
+            static KEY_LABELS: [Label; 1] = [Label::from_static_parts("foo", "bar")];
+            static KEY_DATA: KeyData = KeyData::from_static_parts(&KEY_NAME, &KEY_LABELS);
+
+            b.iter(|| {
+                recorder.increment_counter(Key::Borrowed(&KEY_DATA), 1);
+            })
+        })
+        .with_function("no match", |b| {
+            let patterns = vec!["tokio"];
+            let filter_layer = FilterLayer::from_patterns(patterns);
+            let recorder = filter_layer.layer(NoopRecorder);
+            static KEY_NAME: [SharedString; 1] = [SharedString::const_str("hyper.foo")];
+            static KEY_LABELS: [Label; 1] = [Label::from_static_parts("foo", "bar")];
+            static KEY_DATA: KeyData = KeyData::from_static_parts(&KEY_NAME, &KEY_LABELS);
+
+            b.iter(|| {
+                recorder.increment_counter(Key::Borrowed(&KEY_DATA), 1);
+            })
+        })
+        .with_function("deep match", |b| {
+            let patterns = vec!["tokio"];
+            let filter_layer = FilterLayer::from_patterns(patterns);
+            let recorder = filter_layer.layer(NoopRecorder);
+            static KEY_NAME: [SharedString; 2] = [
+                SharedString::const_str("prefix"),
+                SharedString::const_str("tokio.foo"),
+            ];
+            static KEY_LABELS: [Label; 1] = [Label::from_static_parts("foo", "bar")];
+            static KEY_DATA: KeyData = KeyData::from_static_parts(&KEY_NAME, &KEY_LABELS);
+
+            b.iter(|| {
+                recorder.increment_counter(Key::Borrowed(&KEY_DATA), 1);
+            })
+        })
+        .with_function("noop recorder overhead (increment_counter)", |b| {
+            let recorder = NoopRecorder;
+            static KEY_NAME: [SharedString; 1] = [SharedString::const_str("tokio.foo")];
+            static KEY_LABELS: [Label; 1] = [Label::from_static_parts("foo", "bar")];
+            static KEY_DATA: KeyData = KeyData::from_static_parts(&KEY_NAME, &KEY_LABELS);
+
+            b.iter(|| {
+                recorder.increment_counter(Key::Borrowed(&KEY_DATA), 1);
+            })
+        }),
+    );
+}
+
+criterion_group!(benches, layer_benchmark);
+criterion_main!(benches);

metrics-util/benches/prefix.rs

@@ -0,0 +1,33 @@
+use criterion::{criterion_group, criterion_main, Benchmark, Criterion};
+use metrics::{Key, KeyData, Label, NoopRecorder, Recorder, SharedString};
+use metrics_util::layers::{Layer, PrefixLayer};
+
+fn layer_benchmark(c: &mut Criterion) {
+    c.bench(
+        "prefix",
+        Benchmark::new("basic", |b| {
+            let prefix_layer = PrefixLayer::new("prefix");
+            let recorder = prefix_layer.layer(NoopRecorder);
+            static KEY_NAME: [SharedString; 1] = [SharedString::const_str("simple_key")];
+            static KEY_LABELS: [Label; 1] = [Label::from_static_parts("foo", "bar")];
+            static KEY_DATA: KeyData = KeyData::from_static_parts(&KEY_NAME, &KEY_LABELS);
+
+            b.iter(|| {
+                recorder.increment_counter(Key::Borrowed(&KEY_DATA), 1);
+            })
+        })
+        .with_function("noop recorder overhead (increment_counter)", |b| {
+            let recorder = NoopRecorder;
+            static KEY_NAME: [SharedString; 1] = [SharedString::const_str("simple_key")];
+            static KEY_LABELS: [Label; 1] = [Label::from_static_parts("foo", "bar")];
+            static KEY_DATA: KeyData = KeyData::from_static_parts(&KEY_NAME, &KEY_LABELS);
+
+            b.iter(|| {
+                recorder.increment_counter(Key::Borrowed(&KEY_DATA), 1);
+            })
+        }),
+    );
+}
+
+criterion_group!(benches, layer_benchmark);
+criterion_main!(benches);

metrics-util/benches/registry.rs

@@ -1,5 +1,5 @@
 use criterion::{criterion_group, criterion_main, BatchSize, Benchmark, Criterion};
-use metrics::{Key, KeyData, Label};
+use metrics::{Key, KeyData, Label, SharedString};
 use metrics_util::Registry;
 
 fn registry_benchmark(c: &mut Criterion) {
@@ -7,7 +7,8 @@ fn registry_benchmark(c: &mut Criterion) {
         "registry",
         Benchmark::new("cached op (basic)", |b| {
             let registry: Registry<Key, ()> = Registry::new();
-            static KEY_DATA: KeyData = KeyData::from_static_name("simple_key");
+            static KEY_NAME: [SharedString; 1] = [SharedString::const_str("simple_key")];
+            static KEY_DATA: KeyData = KeyData::from_static_name(&KEY_NAME);
 
             b.iter(|| {
                 let key = Key::Borrowed(&KEY_DATA);
@@ -16,8 +17,9 @@ fn registry_benchmark(c: &mut Criterion) {
         })
         .with_function("cached op (labels)", |b| {
             let registry: Registry<Key, ()> = Registry::new();
+            static KEY_NAME: [SharedString; 1] = [SharedString::const_str("simple_key")];
             static KEY_LABELS: [Label; 1] = [Label::from_static_parts("type", "http")];
-            static KEY_DATA: KeyData = KeyData::from_static_parts("simple_key", &KEY_LABELS);
+            static KEY_DATA: KeyData = KeyData::from_static_parts(&KEY_NAME, &KEY_LABELS);
 
             b.iter(|| {
                 let key = Key::Borrowed(&KEY_DATA);
@@ -67,15 +69,15 @@ fn registry_benchmark(c: &mut Criterion) {
         })
         .with_function("const key data overhead (basic)", |b| {
             b.iter(|| {
-                let key = "simple_key";
+                static KEY_NAME: [SharedString; 1] = [SharedString::const_str("simple_key")];
-                KeyData::from_static_name(key)
+                KeyData::from_static_name(&KEY_NAME)
             })
         })
         .with_function("const key data overhead (labels)", |b| {
             b.iter(|| {
-                let key = "simple_key";
+                static KEY_NAME: [SharedString; 1] = [SharedString::const_str("simple_key")];
                 static LABELS: [Label; 1] = [Label::from_static_parts("type", "http")];
-                KeyData::from_static_parts(key, &LABELS)
+                KeyData::from_static_parts(&KEY_NAME, &LABELS)
             })
         })
         .with_function("owned key overhead (basic)", |b| {
@@ -92,12 +94,14 @@ fn registry_benchmark(c: &mut Criterion) {
             })
         })
         .with_function("cached key overhead (basic)", |b| {
-            static KEY_DATA: KeyData = KeyData::from_static_name("simple_key");
+            static KEY_NAME: [SharedString; 1] = [SharedString::const_str("simple_key")];
+            static KEY_DATA: KeyData = KeyData::from_static_name(&KEY_NAME);
             b.iter(|| Key::Borrowed(&KEY_DATA))
         })
         .with_function("cached key overhead (labels)", |b| {
+            static KEY_NAME: [SharedString; 1] = [SharedString::const_str("simple_key")];
             static KEY_LABELS: [Label; 1] = [Label::from_static_parts("type", "http")];
-            static KEY_DATA: KeyData = KeyData::from_static_parts("simple_key", &KEY_LABELS);
+            static KEY_DATA: KeyData = KeyData::from_static_parts(&KEY_NAME, &KEY_LABELS);
             b.iter(|| Key::Borrowed(&KEY_DATA))
         }),
     );

metrics-util/src/bucket.rs

@@ -5,14 +5,19 @@ use std::{
     sync::atomic::{AtomicUsize, Ordering},
 };
 
-const BLOCK_SIZE: usize = 512;
+#[cfg(target_pointer_width = "16")]
+const BLOCK_SIZE: usize = 16;
+#[cfg(target_pointer_width = "32")]
+const BLOCK_SIZE: usize = 32;
+#[cfg(target_pointer_width = "64")]
+const BLOCK_SIZE: usize = 64;
 
 /// Discrete chunk of values with atomic read/write access.
 struct Block<T> {
     // Write index.
     write: AtomicUsize,
 
-    // Read index.
+    // Read bitmap.
     read: AtomicUsize,
 
     // The individual slots.
@@ -35,7 +40,7 @@ impl<T> Block<T> {
 
     /// Gets the current length of this block.
     pub fn len(&self) -> usize {
-        self.read.load(Ordering::Acquire)
+        self.read.load(Ordering::Acquire).trailing_ones() as usize
     }
 
     /// Gets a slice of the data written to this block.
@@ -71,7 +76,7 @@ impl<T> Block<T> {
         }
 
         // Scoot our read index forward.
-        self.read.fetch_add(1, Ordering::AcqRel);
+        self.read.fetch_or(1 << index, Ordering::AcqRel);
 
         Ok(())
     }
@@ -324,6 +329,7 @@ mod tests {
 
         let result = block.push(42);
         assert!(result.is_ok());
+        assert_eq!(block.len(), 1);
 
         let data = block.data();
         assert_eq!(data.len(), 1);

metrics-util/src/layers/filter.rs

@@ -13,7 +13,9 @@ pub struct Filter<R> {
 
 impl<R> Filter<R> {
     fn should_filter(&self, key: &Key) -> bool {
-        self.automaton.is_match(key.name().as_ref())
+        key.name()
+            .parts()
+            .any(|s| self.automaton.is_match(s.as_ref()))
     }
 }
 
@@ -75,11 +77,14 @@ impl FilterLayer {
     /// Creates a `FilterLayer` from an existing set of patterns.
     pub fn from_patterns<P, I>(patterns: P) -> Self
     where
-        P: Iterator<Item = I>,
+        P: IntoIterator<Item = I>,
         I: AsRef<str>,
     {
         FilterLayer {
-            patterns: patterns.map(|s| s.as_ref().to_string()).collect(),
+            patterns: patterns
+                .into_iter()
+                .map(|s| s.as_ref().to_string())
+                .collect(),
             case_insensitive: false,
             use_dfa: true,
         }
@@ -142,7 +147,7 @@ mod tests {
         let patterns = &["tokio", "bb8"];
         let recorder = DebuggingRecorder::new();
         let snapshotter = recorder.snapshotter();
-        let filter = FilterLayer::from_patterns(patterns.iter());
+        let filter = FilterLayer::from_patterns(patterns);
         let layered = filter.layer(recorder);
 
         let before = snapshotter.snapshot();
@@ -186,7 +191,10 @@ mod tests {
         assert_eq!(after.len(), 2);
 
         for (_kind, key, unit, desc, _value) in after {
-            assert!(!key.name().contains("tokio") && !key.name().contains("bb8"));
+            assert!(
+                !key.name().to_string().contains("tokio")
+                    && !key.name().to_string().contains("bb8")
+            );
             // We cheat here since we're not comparing one-to-one with the source data,
             // but we know which metrics are going to make it through so we can hard code.
             assert_eq!(Some(Unit::Bytes), unit);
@@ -217,8 +225,8 @@ mod tests {
 
         for (_kind, key, _unit, _desc, _value) in &after {
             assert!(
-                !key.name().to_lowercase().contains("tokio")
+                !key.name().to_string().to_lowercase().contains("tokio")
-                    && !key.name().to_lowercase().contains("bb8")
+                    && !key.name().to_string().to_lowercase().contains("bb8")
             );
         }
     }

metrics-util/src/layers/mod.rs

@@ -17,7 +17,12 @@
 //!
 //! impl<R> StairwayDeny<R> {
 //!     fn is_invalid_key(&self, key: &Key) -> bool {
-//!         key.name().contains("stairway") || key.name().contains("heaven")
+//!         for part in key.name().parts() {
+//!             if part.contains("stairway") || part.contains("heaven") {
+//!                 return true
+//!             }
+//!         }
+//!         false
 //!     }
 //! }
 //!

metrics-util/src/layers/prefix.rs

@@ -1,19 +1,17 @@
 use crate::layers::Layer;
-use metrics::{Key, Recorder, Unit};
+use metrics::{Key, Recorder, SharedString, Unit};
 
 /// Applies a prefix to every metric key.
 ///
 /// Keys will be prefixed in the format of `<prefix>.<remaining>`.
 pub struct Prefix<R> {
-    prefix: String,
+    prefix: SharedString,
     inner: R,
 }
 
 impl<R> Prefix<R> {
     fn prefix_key(&self, key: Key) -> Key {
-        key.into_owned()
+        key.into_owned().prepend_name(self.prefix.clone()).into()
-            .map_name(|old| format!("{}.{}", self.prefix, old))
-            .into()
     }
 }
 
@@ -52,12 +50,12 @@ impl<R: Recorder> Recorder for Prefix<R> {
 /// A layer for applying a prefix to every metric key.
 ///
 /// More information on the behavior of the layer can be found in [`Prefix`].
-pub struct PrefixLayer(String);
+pub struct PrefixLayer(&'static str);
 
 impl PrefixLayer {
     /// Creates a new `PrefixLayer` based on the given prefix.
     pub fn new<S: Into<String>>(prefix: S) -> PrefixLayer {
-        PrefixLayer(prefix.into())
+        PrefixLayer(Box::leak(prefix.into().into_boxed_str()))
     }
 }
 
@@ -66,7 +64,7 @@ impl<R> Layer<R> for PrefixLayer {
 
     fn layer(&self, inner: R) -> Self::Output {
         Prefix {
-            prefix: self.0.clone(),
+            prefix: self.0.into(),
             inner,
         }
     }
@@ -115,7 +113,7 @@ mod tests {
         assert_eq!(after.len(), 3);
 
         for (i, (_kind, key, unit, desc, _value)) in after.iter().enumerate() {
-            assert!(key.name().starts_with("testing"));
+            assert!(key.name().to_string().starts_with("testing"));
             assert_eq!(&Some(ud[i].0.clone()), unit);
             assert_eq!(&Some(ud[i].1), desc);
         }

metrics/Cargo.toml

@@ -27,10 +27,15 @@ bench = false
 name = "macros"
 harness = false
 
+[[bench]]
+name = "key"
+harness = false
+
 [dependencies]
 beef = "0.4"
 metrics-macros = { version = "0.1.0-alpha.1", path = "../metrics-macros" }
 proc-macro-hack = "0.5"
+sharded-slab = "0.1"
 
 [dev-dependencies]
 log = "0.4"

metrics/benches/key.rs

@@ -0,0 +1,28 @@
+use criterion::{criterion_group, criterion_main, Benchmark, Criterion};
+
+use metrics::{NameParts, SharedString};
+
+fn key_benchmark(c: &mut Criterion) {
+    c.bench(
+        "key",
+        Benchmark::new("name_parts/to_string", |b| {
+            static NAME_PARTS: [SharedString; 2] = [
+                SharedString::const_str("part1"),
+                SharedString::const_str("part2"),
+            ];
+            let name = NameParts::from_static_names(&NAME_PARTS);
+            b.iter(|| name.to_string())
+        })
+        .with_function("name_parts/Display::to_string", |b| {
+            static NAME_PARTS: [SharedString; 2] = [
+                SharedString::const_str("part1"),
+                SharedString::const_str("part2"),
+            ];
+            let name = NameParts::from_static_names(&NAME_PARTS);
+            b.iter(|| std::fmt::Display::to_string(&name))
+        }),
+    );
+}
+
+criterion_group!(benches, key_benchmark);
+criterion_main!(benches);

metrics/examples/sizes.rs

@@ -0,0 +1,22 @@
+//! This example is purely for development.
+use metrics::{Key, KeyData, Label, NameParts, SharedString};
+use std::borrow::Cow;
+
+fn main() {
+    println!("KeyData: {} bytes", std::mem::size_of::<KeyData>());
+    println!("Key: {} bytes", std::mem::size_of::<Key>());
+    println!("NameParts: {} bytes", std::mem::size_of::<NameParts>());
+    println!("Label: {} bytes", std::mem::size_of::<Label>());
+    println!(
+        "Cow<'static, [Label]>: {} bytes",
+        std::mem::size_of::<Cow<'static, [Label]>>()
+    );
+    println!(
+        "Vec<SharedString>: {} bytes",
+        std::mem::size_of::<Vec<SharedString>>()
+    );
+    println!(
+        "[Option<SharedString>; 2]: {} bytes",
+        std::mem::size_of::<[Option<SharedString>; 2]>()
+    );
+}

metrics/src/common.rs

@@ -1,13 +1,13 @@
-#[cfg(target_pointer_width = "64")]
+use crate::cow::Cow;
-use beef::lean::Cow;
-#[cfg(not(target_pointer_width = "64"))]
-use beef::Cow;
 
 /// An allocation-optimized string.
 ///
 /// We specify `SharedString` to attempt to get the best of both worlds: flexibility to provide a
 /// static or dynamic (owned) string, while retaining the performance benefits of being able to
 /// take ownership of owned strings and borrows of completely static strings.
+///
+/// `SharedString` can be converted to from either `&'static str` or `String`, with a method,
+/// `const_str`, from constructing `SharedString` from `&'static str` in a `const` fashion.
 pub type SharedString = Cow<'static, str>;
 
 /// Units for a given metric.
@@ -16,61 +16,57 @@ pub type SharedString = Cow<'static, str>;
 /// downstream systems natively support defining units and so they can be specified during registration.
 #[derive(Clone, Debug, PartialEq)]
 pub enum Unit {
-    // Dimensionless measurements.
     /// Count.
     Count,
     /// Percentage.
     Percent,
-    // Time measurements.
     /// Seconds.
+    ///
+    /// One second is equal to 1000 milliseconds.
     Seconds,
     /// Milliseconds.
+    ///
+    /// One millisecond is equal to 1000 microseconds.
     Milliseconds,
     /// Microseconds.
+    ///
+    /// One microsecond is equal to 1000 nanoseconds.
     Microseconds,
     /// Nanoseconds.
     Nanoseconds,
-
+    /// Tebibytes.
-    // Data measurement.
+    ///
-    /// Terabytes.
+    /// One tebibyte is equal to 1024 gigibytes.
-    Terabytes,
+    Tebibytes,
-    /// Gigabytes.
+    /// Gigibytes.
-    Gigabytes,
+    ///
-    /// Megabytes.
+    /// One gigibyte is equal to 1024 mebibytes.
-    Megabytes,
+    Gigibytes,
-    /// Kilobytes.
+    /// Mebibytes.
-    Kilobytes,
+    ///
+    /// One mebibyte is equal to 1024 kibibytes.
+    Mebibytes,
+    /// Kibibytes.
+    ///
+    /// One kibibyte is equal to 1024 bytes.
+    Kibibytes,
     /// Bytes.
     Bytes,
-    /// Terabits.
-    Terabits,
-    /// Gigabits.
-    Gigabits,
-    /// Megabits.
-    Megabits,
-    /// Kilobits.
-    Kilobits,
-    /// Bits.
-    Bits,
-
-    // Rate measurements.
-    /// Terabytes per second.
-    TerabytesPerSecond,
-    /// Gigabytes per second.
-    GigabytesPerSecond,
-    /// Megabytes per second.
-    MegabytesPerSecond,
-    /// Kilobytes per second.
-    KilobytesPerSecond,
-    /// Bytes per second.
-    BytesPerSecond,
     /// Terabits per second.
+    ///
+    /// One terabit is equal to 1000 gigabits.
     TerabitsPerSecond,
     /// Gigabits per second.
+    ///
+    /// One gigabit is equal to 1000 megabits.
     GigabitsPerSecond,
     /// Megabits per second.
+    ///
+    /// One megabit is equal to 1000 kilobits.
     MegabitsPerSecond,
     /// Kilobits per second.
+    ///
+    /// One kilobit is equal to 1000 bits.
     KilobitsPerSecond,
     /// Bits per second.
     BitsPerSecond,
@@ -88,21 +84,11 @@ impl Unit {
             Unit::Milliseconds => "milliseconds",
             Unit::Microseconds => "microseconds",
             Unit::Nanoseconds => "nanoseconds",
-            Unit::Terabytes => "terabytes",
+            Unit::Tebibytes => "tebibytes",
-            Unit::Gigabytes => "gigabytes",
+            Unit::Gigibytes => "gigibytes",
-            Unit::Megabytes => "megabytes",
+            Unit::Mebibytes => "mebibytes",
-            Unit::Kilobytes => "kilobytes",
+            Unit::Kibibytes => "kibibytes",
             Unit::Bytes => "bytes",
-            Unit::Terabits => "terabits",
-            Unit::Gigabits => "gigabits",
-            Unit::Megabits => "megabits",
-            Unit::Kilobits => "kilobits",
-            Unit::Bits => "bits",
-            Unit::TerabytesPerSecond => "terabytes_per_second",
-            Unit::GigabytesPerSecond => "gigabytes_per_second",
-            Unit::MegabytesPerSecond => "megabytes_per_second",
-            Unit::KilobytesPerSecond => "kilobytes_per_second",
-            Unit::BytesPerSecond => "bytes_per_second",
             Unit::TerabitsPerSecond => "terabits_per_second",
             Unit::GigabitsPerSecond => "gigabits_per_second",
             Unit::MegabitsPerSecond => "megabits_per_second",
@@ -126,25 +112,15 @@ impl Unit {
             Unit::Milliseconds => "ms",
             Unit::Microseconds => "us",
             Unit::Nanoseconds => "ns",
-            Unit::Terabytes => "TB",
+            Unit::Tebibytes => "TiB",
-            Unit::Gigabytes => "Gb",
+            Unit::Gigibytes => "GiB",
-            Unit::Megabytes => "MB",
+            Unit::Mebibytes => "MiB",
-            Unit::Kilobytes => "KB",
+            Unit::Kibibytes => "KiB",
             Unit::Bytes => "B",
-            Unit::Terabits => "Tb",
-            Unit::Gigabits => "Gb",
-            Unit::Megabits => "Mb",
-            Unit::Kilobits => "Kb",
-            Unit::Bits => "b",
-            Unit::TerabytesPerSecond => "TBps",
-            Unit::GigabytesPerSecond => "GBps",
-            Unit::MegabytesPerSecond => "MBps",
-            Unit::KilobytesPerSecond => "KBps",
-            Unit::BytesPerSecond => "Bps",
             Unit::TerabitsPerSecond => "Tbps",
             Unit::GigabitsPerSecond => "Gbps",
             Unit::MegabitsPerSecond => "Mbps",
-            Unit::KilobitsPerSecond => "Kbps",
+            Unit::KilobitsPerSecond => "kbps",
             Unit::BitsPerSecond => "bps",
             Unit::CountPerSecond => "/s",
         }
@@ -161,21 +137,11 @@ impl Unit {
             "milliseconds" => Some(Unit::Milliseconds),
             "microseconds" => Some(Unit::Microseconds),
             "nanoseconds" => Some(Unit::Nanoseconds),
-            "terabytes" => Some(Unit::Terabytes),
+            "tebibytes" => Some(Unit::Tebibytes),
-            "gigabytes" => Some(Unit::Gigabytes),
+            "gigibytes" => Some(Unit::Gigibytes),
-            "megabytes" => Some(Unit::Megabytes),
+            "mebibytes" => Some(Unit::Mebibytes),
-            "kilobytes" => Some(Unit::Kilobytes),
+            "kibibytes" => Some(Unit::Kibibytes),
             "bytes" => Some(Unit::Bytes),
-            "terabits" => Some(Unit::Terabits),
-            "gigabits" => Some(Unit::Gigabits),
-            "megabits" => Some(Unit::Megabits),
-            "kilobits" => Some(Unit::Kilobits),
-            "bits" => Some(Unit::Bits),
-            "terabytes_per_second" => Some(Unit::TerabytesPerSecond),
-            "gigabytes_per_second" => Some(Unit::GigabytesPerSecond),
-            "megabytes_per_second" => Some(Unit::MegabytesPerSecond),
-            "kilobytes_per_second" => Some(Unit::KilobytesPerSecond),
-            "bytes_per_second" => Some(Unit::BytesPerSecond),
             "terabits_per_second" => Some(Unit::TerabitsPerSecond),
             "gigabits_per_second" => Some(Unit::GigabitsPerSecond),
             "megabits_per_second" => Some(Unit::MegabitsPerSecond),
@@ -197,21 +163,11 @@ impl Unit {
     /// Whether or not this unit relates to the measurement of data.
     pub fn is_data_based(&self) -> bool {
         match self {
-            Unit::Terabytes
+            Unit::Tebibytes
-            | Unit::Gigabytes
+            | Unit::Gigibytes
-            | Unit::Megabytes
+            | Unit::Mebibytes
-            | Unit::Kilobytes
+            | Unit::Kibibytes
             | Unit::Bytes
-            | Unit::Terabits
-            | Unit::Gigabits
-            | Unit::Megabits
-            | Unit::Kilobits
-            | Unit::Bits
-            | Unit::TerabytesPerSecond
-            | Unit::GigabytesPerSecond
-            | Unit::MegabytesPerSecond
-            | Unit::KilobytesPerSecond
-            | Unit::BytesPerSecond
             | Unit::TerabitsPerSecond
             | Unit::GigabitsPerSecond
             | Unit::MegabitsPerSecond
@@ -224,13 +180,8 @@ impl Unit {
     /// Whether or not this unit relates to the measurement of data rates.
     pub fn is_data_rate_based(&self) -> bool {
         match self {
-            Unit::TerabytesPerSecond
+            Unit::TerabitsPerSecond
-            | Unit::GigabytesPerSecond
+            | Unit::GigabitsPerSecond
-            | Unit::MegabytesPerSecond
-            | Unit::KilobytesPerSecond
-            | Unit::BytesPerSecond
-            | Unit::TerabitsPerSecond
-            | Unit::Gigabits
             | Unit::MegabitsPerSecond
             | Unit::KilobitsPerSecond
             | Unit::BitsPerSecond => true,
@@ -265,3 +216,37 @@ impl IntoU64 for core::time::Duration {
 pub fn __into_u64<V: IntoU64>(value: V) -> u64 {
     value.into_u64()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::Unit;
+
+    #[test]
+    fn test_unit_conversions() {
+        let all_variants = vec![
+            Unit::Count,
+            Unit::Percent,
+            Unit::Seconds,
+            Unit::Milliseconds,
+            Unit::Microseconds,
+            Unit::Nanoseconds,
+            Unit::Tebibytes,
+            Unit::Gigibytes,
+            Unit::Mebibytes,
+            Unit::Kibibytes,
+            Unit::Bytes,
+            Unit::TerabitsPerSecond,
+            Unit::GigabitsPerSecond,
+            Unit::MegabitsPerSecond,
+            Unit::KilobitsPerSecond,
+            Unit::BitsPerSecond,
+            Unit::CountPerSecond,
+        ];
+
+        for variant in all_variants {
+            let s = variant.as_str();
+            let parsed = Unit::from_str(s);
+            assert_eq!(Some(variant), parsed);
+        }
+    }
+}

metrics/src/cow.rs

@@ -0,0 +1,515 @@
+use crate::label::Label;
+use alloc::borrow::Borrow;
+use alloc::string::String;
+use alloc::vec::Vec;
+use core::cmp::Ordering;
+use core::fmt;
+use core::hash::{Hash, Hasher};
+use core::marker::PhantomData;
+use core::mem::ManuallyDrop;
+use core::ptr::{slice_from_raw_parts, NonNull};
+
+/// A clone-on-write smart pointer with an optimized memory layout.
+pub struct Cow<'a, T: Cowable + ?Sized + 'a> {
+    /// Pointer to data.
+    ptr: NonNull<T::Pointer>,
+
+    /// Pointer metadata: length and capacity.
+    meta: Metadata,
+
+    /// Lifetime marker.
+    marker: PhantomData<&'a T>,
+}
+
+impl<T> Cow<'_, T>
+where
+    T: Cowable + ?Sized,
+{
+    #[inline]
+    pub fn owned(val: T::Owned) -> Self {
+        let (ptr, meta) = T::owned_into_parts(val);
+
+        Cow {
+            ptr,
+            meta,
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'a, T> Cow<'a, T>
+where
+    T: Cowable + ?Sized,
+{
+    #[inline]
+    pub fn borrowed(val: &'a T) -> Self {
+        let (ptr, meta) = T::ref_into_parts(val);
+
+        Cow {
+            ptr,
+            meta,
+            marker: PhantomData,
+        }
+    }
+
+    #[inline]
+    pub fn into_owned(self) -> T::Owned {
+        let cow = ManuallyDrop::new(self);
+
+        if cow.is_borrowed() {
+            unsafe { T::clone_from_parts(cow.ptr, &cow.meta) }
+        } else {
+            unsafe { T::owned_from_parts(cow.ptr, &cow.meta) }
+        }
+    }
+
+    #[inline]
+    pub fn is_borrowed(&self) -> bool {
+        self.meta.capacity() == 0
+    }
+
+    #[inline]
+    pub fn is_owned(&self) -> bool {
+        self.meta.capacity() != 0
+    }
+
+    #[inline]
+    fn borrow(&self) -> &T {
+        unsafe { &*T::ref_from_parts(self.ptr, &self.meta) }
+    }
+}
+
+// Implementations of constant functions for creating `Cow` via static strings, static string
+// slices, and static label slices.
+impl<'a> Cow<'a, str> {
+    pub const fn const_str(val: &'a str) -> Self {
+        Cow {
+            // We are casting *const T to *mut T, however for all borrowed values
+            // this raw pointer is only ever dereferenced back to &T.
+            ptr: unsafe { NonNull::new_unchecked(val.as_ptr() as *mut u8) },
+            meta: Metadata::from_ref(val.len()),
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'a> Cow<'a, [Cow<'static, str>]> {
+    pub const fn const_slice(val: &'a [Cow<'static, str>]) -> Self {
+        Cow {
+            ptr: unsafe { NonNull::new_unchecked(val.as_ptr() as *mut Cow<'static, str>) },
+            meta: Metadata::from_ref(val.len()),
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<'a> Cow<'a, [Label]> {
+    pub const fn const_slice(val: &'a [Label]) -> Self {
+        Cow {
+            ptr: unsafe { NonNull::new_unchecked(val.as_ptr() as *mut Label) },
+            meta: Metadata::from_ref(val.len()),
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<T> Hash for Cow<'_, T>
+where
+    T: Hash + Cowable + ?Sized,
+{
+    #[inline]
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.borrow().hash(state)
+    }
+}
+
+impl<'a, T> Default for Cow<'a, T>
+where
+    T: Cowable + ?Sized,
+    &'a T: Default,
+{
+    #[inline]
+    fn default() -> Self {
+        Cow::borrowed(Default::default())
+    }
+}
+
+impl<T> Eq for Cow<'_, T> where T: Eq + Cowable + ?Sized {}
+
+impl<A, B> PartialOrd<Cow<'_, B>> for Cow<'_, A>
+where
+    A: Cowable + ?Sized + PartialOrd<B>,
+    B: Cowable + ?Sized,
+{
+    #[inline]
+    fn partial_cmp(&self, other: &Cow<'_, B>) -> Option<Ordering> {
+        PartialOrd::partial_cmp(self.borrow(), other.borrow())
+    }
+}
+
+impl<T> Ord for Cow<'_, T>
+where
+    T: Ord + Cowable + ?Sized,
+{
+    #[inline]
+    fn cmp(&self, other: &Self) -> Ordering {
+        Ord::cmp(self.borrow(), other.borrow())
+    }
+}
+
+impl<'a, T> From<&'a T> for Cow<'a, T>
+where
+    T: Cowable + ?Sized,
+{
+    #[inline]
+    fn from(val: &'a T) -> Self {
+        Cow::borrowed(val)
+    }
+}
+
+impl From<String> for Cow<'_, str> {
+    #[inline]
+    fn from(s: String) -> Self {
+        Cow::owned(s)
+    }
+}
+
+impl From<Vec<Label>> for Cow<'_, [Label]> {
+    #[inline]
+    fn from(v: Vec<Label>) -> Self {
+        Cow::owned(v)
+    }
+}
+
+impl From<Vec<Cow<'static, str>>> for Cow<'_, [Cow<'static, str>]> {
+    #[inline]
+    fn from(v: Vec<Cow<'static, str>>) -> Self {
+        Cow::owned(v)
+    }
+}
+
+impl<T> Drop for Cow<'_, T>
+where
+    T: Cowable + ?Sized,
+{
+    #[inline]
+    fn drop(&mut self) {
+        if self.is_owned() {
+            unsafe { T::owned_from_parts(self.ptr, &self.meta) };
+        }
+    }
+}
+
+impl<'a, T> Clone for Cow<'a, T>
+where
+    T: Cowable + ?Sized,
+{
+    #[inline]
+    fn clone(&self) -> Self {
+        if self.is_owned() {
+            // Gotta clone the actual inner value.
+            Cow::owned(unsafe { T::clone_from_parts(self.ptr, &self.meta) })
+        } else {
+            Cow { ..*self }
+        }
+    }
+}
+
+impl<T> core::ops::Deref for Cow<'_, T>
+where
+    T: Cowable + ?Sized,
+{
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &T {
+        self.borrow()
+    }
+}
+
+impl<T> AsRef<T> for Cow<'_, T>
+where
+    T: Cowable + ?Sized,
+{
+    #[inline]
+    fn as_ref(&self) -> &T {
+        self.borrow()
+    }
+}
+
+impl<T> Borrow<T> for Cow<'_, T>
+where
+    T: Cowable + ?Sized,
+{
+    #[inline]
+    fn borrow(&self) -> &T {
+        self.borrow()
+    }
+}
+
+impl<A, B> PartialEq<Cow<'_, B>> for Cow<'_, A>
+where
+    A: Cowable + ?Sized,
+    B: Cowable + ?Sized,
+    A: PartialEq<B>,
+{
+    fn eq(&self, other: &Cow<B>) -> bool {
+        self.borrow() == other.borrow()
+    }
+}
+
+impl<T> fmt::Debug for Cow<'_, T>
+where
+    T: Cowable + fmt::Debug + ?Sized,
+{
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.borrow().fmt(f)
+    }
+}
+
+impl<T> fmt::Display for Cow<'_, T>
+where
+    T: Cowable + fmt::Display + ?Sized,
+{
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.borrow().fmt(f)
+    }
+}
+
+unsafe impl<T: Cowable + Sync + ?Sized> Sync for Cow<'_, T> {}
+unsafe impl<T: Cowable + Send + ?Sized> Send for Cow<'_, T> {}
+
+/// Helper trait required by `Cow<T>` to extract capacity of owned
+/// variant of `T`, and manage conversions.
+///
+/// This can be only implemented on types that match requirements:
+///
+/// + `T::Owned` has a `capacity`, which is an extra word that is absent in `T`.
+/// + `T::Owned` with `capacity` of `0` does not allocate memory.
+/// + `T::Owned` can be reconstructed from `*mut T` borrowed out of it, plus capacity.
+pub unsafe trait Cowable {
+    type Pointer;
+    type Owned;
+
+    fn ref_into_parts(&self) -> (NonNull<Self::Pointer>, Metadata);
+    fn owned_into_parts(owned: Self::Owned) -> (NonNull<Self::Pointer>, Metadata);
+
+    unsafe fn ref_from_parts(ptr: NonNull<Self::Pointer>, metadata: &Metadata) -> *const Self;
+    unsafe fn owned_from_parts(ptr: NonNull<Self::Pointer>, metadata: &Metadata) -> Self::Owned;
+    unsafe fn clone_from_parts(ptr: NonNull<Self::Pointer>, metadata: &Metadata) -> Self::Owned;
+}
+
+unsafe impl Cowable for str {
+    type Pointer = u8;
+    type Owned = String;
+
+    #[inline]
+    fn ref_into_parts(&self) -> (NonNull<u8>, Metadata) {
+        // A note on soundness:
+        //
+        // We are casting *const T to *mut T, however for all borrowed values
+        // this raw pointer is only ever dereferenced back to &T.
+        let ptr = unsafe { NonNull::new_unchecked(self.as_ptr() as *mut _) };
+        let metadata = Metadata::from_ref(self.len());
+        (ptr, metadata)
+    }
+
+    #[inline]
+    unsafe fn ref_from_parts(ptr: NonNull<u8>, metadata: &Metadata) -> *const str {
+        slice_from_raw_parts(ptr.as_ptr(), metadata.length()) as *const _
+    }
+
+    #[inline]
+    fn owned_into_parts(owned: String) -> (NonNull<u8>, Metadata) {
+        let mut owned = ManuallyDrop::new(owned);
+        let ptr = unsafe { NonNull::new_unchecked(owned.as_mut_ptr()) };
+        let metadata = Metadata::from_owned(owned.len(), owned.capacity());
+        (ptr, metadata)
+    }
+
+    #[inline]
+    unsafe fn owned_from_parts(ptr: NonNull<u8>, metadata: &Metadata) -> String {
+        String::from_utf8_unchecked(Vec::from_raw_parts(
+            ptr.as_ptr(),
+            metadata.length(),
+            metadata.capacity(),
+        ))
+    }
+
+    #[inline]
+    unsafe fn clone_from_parts(ptr: NonNull<u8>, metadata: &Metadata) -> Self::Owned {
+        let str = Self::ref_from_parts(ptr, metadata);
+        str.as_ref().unwrap().to_string()
+    }
+}
+
+unsafe impl<'a> Cowable for [Cow<'a, str>] {
+    type Pointer = Cow<'a, str>;
+    type Owned = Vec<Cow<'a, str>>;
+
+    #[inline]
+    fn ref_into_parts(&self) -> (NonNull<Cow<'a, str>>, Metadata) {
+        // A note on soundness:
+        //
+        // We are casting *const T to *mut T, however for all borrowed values
+        // this raw pointer is only ever dereferenced back to &T.
+        let ptr = unsafe { NonNull::new_unchecked(self.as_ptr() as *mut _) };
+        let metadata = Metadata::from_ref(self.len());
+        (ptr, metadata)
+    }
+
+    #[inline]
+    unsafe fn ref_from_parts(
+        ptr: NonNull<Cow<'a, str>>,
+        metadata: &Metadata,
+    ) -> *const [Cow<'a, str>] {
+        slice_from_raw_parts(ptr.as_ptr(), metadata.length())
+    }
+
+    #[inline]
+    fn owned_into_parts(owned: Vec<Cow<'a, str>>) -> (NonNull<Cow<'a, str>>, Metadata) {
+        let mut owned = ManuallyDrop::new(owned);
+        let ptr = unsafe { NonNull::new_unchecked(owned.as_mut_ptr()) };
+        let metadata = Metadata::from_owned(owned.len(), owned.capacity());
+        (ptr, metadata)
+    }
+
+    #[inline]
+    unsafe fn owned_from_parts(
+        ptr: NonNull<Cow<'a, str>>,
+        metadata: &Metadata,
+    ) -> Vec<Cow<'a, str>> {
+        Vec::from_raw_parts(ptr.as_ptr(), metadata.length(), metadata.capacity())
+    }
+
+    #[inline]
+    unsafe fn clone_from_parts(ptr: NonNull<Cow<'a, str>>, metadata: &Metadata) -> Self::Owned {
+        let ptr = Self::ref_from_parts(ptr, metadata);
+        let xs = ptr.as_ref().unwrap();
+        let mut owned = Vec::with_capacity(xs.len() + 1);
+        owned.extend_from_slice(xs);
+        owned
+    }
+}
+
+unsafe impl Cowable for [Label] {
+    type Pointer = Label;
+    type Owned = Vec<Label>;
+
+    #[inline]
+    fn ref_into_parts(&self) -> (NonNull<Label>, Metadata) {
+        // A note on soundness:
+        //
+        // We are casting *const T to *mut T, however for all borrowed values
+        // this raw pointer is only ever dereferenced back to &T.
+        let ptr = unsafe { NonNull::new_unchecked(self.as_ptr() as *mut _) };
+        let metadata = Metadata::from_ref(self.len());
+        (ptr, metadata)
+    }
+
+    #[inline]
+    unsafe fn ref_from_parts(ptr: NonNull<Label>, metadata: &Metadata) -> *const [Label] {
+        slice_from_raw_parts(ptr.as_ptr(), metadata.length())
+    }
+
+    #[inline]
+    fn owned_into_parts(owned: Vec<Label>) -> (NonNull<Label>, Metadata) {
+        let mut owned = ManuallyDrop::new(owned);
+        let ptr = unsafe { NonNull::new_unchecked(owned.as_mut_ptr()) };
+        let metadata = Metadata::from_owned(owned.len(), owned.capacity());
+        (ptr, metadata)
+    }
+
+    #[inline]
+    unsafe fn owned_from_parts(ptr: NonNull<Label>, metadata: &Metadata) -> Vec<Label> {
+        Vec::from_raw_parts(ptr.as_ptr(), metadata.length(), metadata.capacity())
+    }
+
+    #[inline]
+    unsafe fn clone_from_parts(ptr: NonNull<Label>, metadata: &Metadata) -> Self::Owned {
+        let xs = Self::ref_from_parts(ptr, metadata);
+        xs.as_ref().unwrap().to_vec()
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub struct Metadata(usize, usize);
+
+impl Metadata {
+    #[inline]
+    fn length(&self) -> usize {
+        self.0
+    }
+
+    #[inline]
+    fn capacity(&self) -> usize {
+        self.1
+    }
+
+    pub const fn from_ref(len: usize) -> Metadata {
+        Metadata(len, 0)
+    }
+
+    pub const fn from_owned(len: usize, capacity: usize) -> Metadata {
+        Metadata(len, capacity)
+    }
+
+    pub const fn borrowed() -> Metadata {
+        Metadata(0, 0)
+    }
+
+    pub const fn owned() -> Metadata {
+        Metadata(0, 1)
+    }
+}
+
+/*
+
+This can be enabled again when we have a way to do panics/asserts in stable Rust,
+since const panicking is behind a feature flag at the moment.
+
+const MASK_LO: usize = u32::MAX as usize;
+const MASK_HI: usize = !MASK_LO;
+
+#[cfg(target_pointer_width = "64")]
+impl Metadata {
+    #[inline]
+    fn length(&self) -> usize {
+        self.0 & MASK_LO
+    }
+
+    #[inline]
+    fn capacity(&self) -> usize {
+        self.0 & MASK_HI
+    }
+
+    pub const fn from_ref(len: usize) -> Metadata {
+        if len & MASK_HI != 0 {
+            panic!("Cow: length out of bounds for referenced value");
+        }
+
+        Metadata(len)
+    }
+
+    pub const fn from_owned(len: usize, capacity: usize) -> Metadata {
+        if len & MASK_HI != 0 {
+            panic!("Cow: length out of bounds for owned value");
+        }
+
+        if capacity & MASK_HI != 0 {
+            panic!("Cow: capacity out of bounds for owned value");
+        }
+
+        Metadata((capacity & MASK_LO) << 32 | len & MASK_LO)
+    }
+
+    pub const fn borrowed() -> Metadata {
+        Metadata(0)
+    }
+
+    pub const fn owned() -> Metadata {
+        Metadata(1 << 32)
+    }
+}*/

metrics/src/key.rs

@@ -1,5 +1,5 @@
-use crate::{IntoLabels, Label, SharedString};
+use crate::{cow::Cow, IntoLabels, Label, SharedString};
-use alloc::{borrow::Cow, string::String, vec::Vec};
+use alloc::{string::String, vec::Vec};
 use core::{
     fmt,
     hash::{Hash, Hasher},
@@ -7,13 +7,95 @@ use core::{
     slice::Iter,
 };
 
+const NO_LABELS: [Label; 0] = [];
+
+/// Parts compromising a metric name.
+#[derive(PartialEq, Eq, Hash, Clone, Debug)]
+pub struct NameParts(Cow<'static, [SharedString]>);
+
+impl NameParts {
+    /// Creates a [`NameParts`] from the given name.
+    pub fn from_name<N: Into<SharedString>>(name: N) -> Self {
+        NameParts(Cow::owned(vec![name.into()]))
+    }
+
+    /// Creates a [`NameParts`] from the given static name.
+    pub const fn from_static_names(names: &'static [SharedString]) -> Self {
+        NameParts(Cow::<'static, [SharedString]>::const_slice(names))
+    }
+
+    /// Appends a name part.
+    pub fn append<S: Into<SharedString>>(self, part: S) -> Self {
+        let mut parts = self.0.into_owned();
+        parts.push(part.into());
+        NameParts(Cow::owned(parts))
+    }
+
+    /// Prepends a name part.
+    pub fn prepend<S: Into<SharedString>>(self, part: S) -> Self {
+        let mut parts = self.0.into_owned();
+        parts.insert(0, part.into());
+        NameParts(Cow::owned(parts))
+    }
+
+    /// Gets a reference to the parts for this name.
+    pub fn parts(&self) -> Iter<'_, SharedString> {
+        self.0.iter()
+    }
+
+    /// Renders the name parts as a dot-delimited string.
+    pub fn to_string(&self) -> String {
+        // It's faster to allocate the string by hand instead of collecting the parts and joining
+        // them, or deferring to Dsiplay::to_string, or anything else.  This may change in the
+        // future, or benefit from some sort of string pooling, but otherwise, this seemingly
+        // suboptimal approach -- oh no, a single allocation! :P -- works pretty well overall.
+        let mut first = false;
+        let mut s = String::with_capacity(16);
+        for p in self.0.iter() {
+            if first {
+                s.push_str(".");
+                first = false;
+            }
+            s.push_str(p.as_ref());
+        }
+        s
+    }
+}
+
+impl From<String> for NameParts {
+    fn from(name: String) -> NameParts {
+        NameParts::from_name(name)
+    }
+}
+
+impl From<&'static str> for NameParts {
+    fn from(name: &'static str) -> NameParts {
+        NameParts::from_name(name)
+    }
+}
+
+impl From<&'static [SharedString]> for NameParts {
+    fn from(names: &'static [SharedString]) -> NameParts {
+        NameParts::from_static_names(names)
+    }
+}
+
+impl fmt::Display for NameParts {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let s = self.to_string();
+        f.write_str(s.as_str())?;
+        Ok(())
+    }
+}
+
 /// Inner representation of [`Key`].
 ///
-/// While [`Key`] is the type that users will interact with via [`Recorder`][crate::Recorder`,
+/// While [`Key`] is the type that users will interact with via [`Recorder`][crate::Recorder],
 /// [`KeyData`] is responsible for the actual storage of the name and label data.
 #[derive(PartialEq, Eq, Hash, Clone, Debug)]
 pub struct KeyData {
-    name: SharedString,
+    // TODO: once const slicing is possible on stable, we could likely use `beef` for both of these
+    name_parts: NameParts,
     labels: Cow<'static, [Label]>,
 }
 
@@ -23,44 +105,47 @@ impl KeyData {
     where
         N: Into<SharedString>,
     {
-        Self::from_parts(name, Vec::new())
+        Self {
+            name_parts: NameParts::from_name(name),
+            labels: Cow::owned(Vec::new()),
+        }
     }
 
-    /// Creates a [`KeyData`] from a name and vector of [`Label`]s.
+    /// Creates a [`KeyData`] from a name and set of labels.
     pub fn from_parts<N, L>(name: N, labels: L) -> Self
     where
-        N: Into<SharedString>,
+        N: Into<NameParts>,
         L: IntoLabels,
     {
         Self {
-            name: name.into(),
+            name_parts: name.into(),
-            labels: labels.into_labels().into(),
+            labels: Cow::owned(labels.into_labels()),
         }
     }
 
     /// Creates a [`KeyData`] from a static name.
     ///
     /// This function is `const`, so it can be used in a static context.
-    pub const fn from_static_name(name: &'static str) -> Self {
+    pub const fn from_static_name(name_parts: &'static [SharedString]) -> Self {
-        Self {
+        Self::from_static_parts(name_parts, &NO_LABELS)
-            name: SharedString::const_str(name),
-            labels: Cow::Owned(Vec::new()),
-        }
     }
 
     /// Creates a [`KeyData`] from a static name and static set of labels.
     ///
     /// This function is `const`, so it can be used in a static context.
-    pub const fn from_static_parts(name: &'static str, labels: &'static [Label]) -> Self {
+    pub const fn from_static_parts(
+        name_parts: &'static [SharedString],
+        labels: &'static [Label],
+    ) -> Self {
         Self {
-            name: SharedString::const_str(name),
+            name_parts: NameParts::from_static_names(name_parts),
-            labels: Cow::Borrowed(labels),
+            labels: Cow::<[Label]>::const_slice(labels),
         }
     }
 
-    /// Name of this key.
+    /// Name parts of this key.
-    pub fn name(&self) -> &SharedString {
+    pub fn name(&self) -> &NameParts {
-        &self.name
+        &self.name_parts
     }
 
     /// Labels of this key, if they exist.
@@ -68,21 +153,27 @@ impl KeyData {
         self.labels.iter()
     }
 
-    /// Map the name of this key to a new name, based on `f`.
+    /// Appends a part to the name,
-    ///
+    pub fn append_name<S: Into<SharedString>>(self, part: S) -> Self {
-    /// The value returned by `f` becomes the new name of the key.
+        let name_parts = self.name_parts.append(part);
-    pub fn map_name<F>(mut self, f: F) -> Self
+        Self {
-    where
+            name_parts,
-        F: Fn(SharedString) -> String,
+            labels: self.labels,
-    {
+        }
-        let new_name = f(self.name);
-        self.name = new_name.into();
-        self
     }
 
-    /// Consumes this [`Key`], returning the name and any labels.
+    /// Prepends a part to the name.
-    pub fn into_parts(self) -> (SharedString, Vec<Label>) {
+    pub fn prepend_name<S: Into<SharedString>>(self, part: S) -> Self {
-        (self.name, self.labels.into_owned())
+        let name_parts = self.name_parts.prepend(part);
+        Self {
+            name_parts,
+            labels: self.labels,
+        }
+    }
+
+    /// Consumes this [`Key`], returning the name parts and any labels.
+    pub fn into_parts(self) -> (NameParts, Vec<Label>) {
+        (self.name_parts.clone(), self.labels.into_owned())
     }
 
     /// Clones this [`Key`], and expands the existing set of labels.
@@ -91,12 +182,12 @@ impl KeyData {
             return self.clone();
         }
 
-        let name = self.name.clone();
+        let name_parts = self.name_parts.clone();
         let mut labels = self.labels.clone().into_owned();
         labels.extend(extra_labels);
 
         Self {
-            name,
+            name_parts,
             labels: labels.into(),
         }
     }
@@ -105,9 +196,9 @@ impl KeyData {
 impl fmt::Display for KeyData {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         if self.labels.is_empty() {
-            write!(f, "KeyData({})", self.name)
+            write!(f, "KeyData({})", self.name_parts)
         } else {
-            write!(f, "KeyData({}, [", self.name)?;
+            write!(f, "KeyData({}, [", self.name_parts)?;
             let mut first = true;
             for label in self.labels.as_ref() {
                 if first {
@@ -140,7 +231,10 @@ where
     L: IntoLabels,
 {
     fn from(parts: (N, L)) -> Self {
-        Self::from_parts(parts.0, parts.1)
+        Self {
+            name_parts: NameParts::from_name(parts.0),
+            labels: Cow::owned(parts.1.into_labels()),
+        }
     }
 }
 
@@ -241,12 +335,14 @@ impl From<&'static KeyData> for Key {
 #[cfg(test)]
 mod tests {
     use super::{Key, KeyData};
-    use crate::Label;
+    use crate::{Label, SharedString};
     use std::collections::HashMap;
 
-    static BORROWED_BASIC: KeyData = KeyData::from_static_name("name");
+    static BORROWED_NAME: [SharedString; 1] = [SharedString::const_str("name")];
+    static FOOBAR_NAME: [SharedString; 1] = [SharedString::const_str("foobar")];
+    static BORROWED_BASIC: KeyData = KeyData::from_static_name(&BORROWED_NAME);
     static LABELS: [Label; 1] = [Label::from_static_parts("key", "value")];
-    static BORROWED_LABELS: KeyData = KeyData::from_static_parts("name", &LABELS);
+    static BORROWED_LABELS: KeyData = KeyData::from_static_parts(&BORROWED_NAME, &LABELS);
 
     #[test]
     fn test_keydata_eq_and_hash() {
@@ -262,7 +358,7 @@ mod tests {
         assert_eq!(previous, Some(&42));
 
         let labels = LABELS.to_vec();
-        let owned_labels = KeyData::from_parts("name", labels);
+        let owned_labels = KeyData::from_parts(&BORROWED_NAME[..], labels);
         assert_eq!(&owned_labels, &BORROWED_LABELS);
 
         let previous = keys.insert(owned_labels, 43);
@@ -287,7 +383,7 @@ mod tests {
         assert_eq!(previous, Some(&42));
 
         let labels = LABELS.to_vec();
-        let owned_labels = Key::from(KeyData::from_parts("name", labels));
+        let owned_labels = Key::from(KeyData::from_parts(&BORROWED_NAME[..], labels));
         let borrowed_labels = Key::from(&BORROWED_LABELS);
         assert_eq!(owned_labels, borrowed_labels);
 
@@ -304,19 +400,19 @@ mod tests {
         let result1 = key1.to_string();
         assert_eq!(result1, "KeyData(foobar)");
 
-        let key2 = KeyData::from_parts("foobar", vec![Label::new("system", "http")]);
+        let key2 = KeyData::from_parts(&FOOBAR_NAME[..], vec![Label::new("system", "http")]);
         let result2 = key2.to_string();
         assert_eq!(result2, "KeyData(foobar, [system = http])");
 
         let key3 = KeyData::from_parts(
-            "foobar",
+            &FOOBAR_NAME[..],
             vec![Label::new("system", "http"), Label::new("user", "joe")],
         );
         let result3 = key3.to_string();
         assert_eq!(result3, "KeyData(foobar, [system = http, user = joe])");
 
         let key4 = KeyData::from_parts(
-            "foobar",
+            &FOOBAR_NAME[..],
             vec![
                 Label::new("black", "black"),
                 Label::new("lives", "lives"),
@@ -335,8 +431,10 @@ mod tests {
         let owned_a = KeyData::from_name("a");
         let owned_b = KeyData::from_name("b");
 
-        static STATIC_A: KeyData = KeyData::from_static_name("a");
+        static A_NAME: [SharedString; 1] = [SharedString::const_str("a")];
-        static STATIC_B: KeyData = KeyData::from_static_name("b");
+        static STATIC_A: KeyData = KeyData::from_static_name(&A_NAME);
+        static B_NAME: [SharedString; 1] = [SharedString::const_str("b")];
+        static STATIC_B: KeyData = KeyData::from_static_name(&B_NAME);
 
         assert_eq!(Key::Owned(owned_a.clone()), Key::Owned(owned_a.clone()));
         assert_eq!(Key::Owned(owned_b.clone()), Key::Owned(owned_b.clone()));

metrics/src/lib.rs

@@ -223,6 +223,8 @@ use proc_macro_hack::proc_macro_hack;
 mod common;
 pub use self::common::*;
 
+mod cow;
+
 mod key;
 pub use self::key::*;