From 30c7ff1a98b4f621720a95878a9a8f2e45870bdb Mon Sep 17 00:00:00 2001
From: Toby Lawrence <toby@nuclearfurnace.com>
Date: Fri, 13 Nov 2020 11:06:53 -0500
Subject: [PATCH] a lot of tweaks

---
 .../src/tracing_integration.rs                |   2 +-
 metrics-util/Cargo.toml                       |   4 +
 metrics-util/benches/filter.rs                |  61 +++
 metrics-util/src/layers/filter.rs             |  22 +-
 metrics/src/cow.rs                            | 515 ++++++++++++++++++
 5 files changed, 596 insertions(+), 8 deletions(-)
 create mode 100644 metrics-util/benches/filter.rs
 create mode 100644 metrics/src/cow.rs

diff --git a/metrics-tracing-context/src/tracing_integration.rs b/metrics-tracing-context/src/tracing_integration.rs
index f55b8a4..37381ae 100644
--- a/metrics-tracing-context/src/tracing_integration.rs
+++ b/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);
     }
 
diff --git a/metrics-util/Cargo.toml b/metrics-util/Cargo.toml
index 40c7ff0..ae2da86 100644
--- a/metrics-util/Cargo.toml
+++ b/metrics-util/Cargo.toml
@@ -30,6 +30,10 @@ harness = false
 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 }
diff --git a/metrics-util/benches/filter.rs b/metrics-util/benches/filter.rs
new file mode 100644
index 0000000..ac5b73d
--- /dev/null
+++ b/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);
diff --git a/metrics-util/src/layers/filter.rs b/metrics-util/src/layers/filter.rs
index 83ce19d..95c59bf 100644
--- a/metrics-util/src/layers/filter.rs
+++ b/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_lowercase().contains("bb8")
+                !key.name().to_string().to_lowercase().contains("tokio")
+                    && !key.name().to_string().to_lowercase().contains("bb8")
             );
         }
     }
diff --git a/metrics/src/cow.rs b/metrics/src/cow.rs
new file mode 100644
index 0000000..862fc5e
--- /dev/null
+++ b/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)
+    }
+}*/