From 2448ca9cdc7c2ad59925e440056e2beb6c30bcf5 Mon Sep 17 00:00:00 2001
From: Carl Lerche <me@carllerche.com>
Date: Fri, 29 Mar 2019 14:24:43 -0700
Subject: [PATCH] balance: cleanup example (#211)

---
 tower-balance/Cargo.toml       |   1 +
 tower-balance/examples/demo.rs | 244 ++++++---------------------------
 2 files changed, 40 insertions(+), 205 deletions(-)

diff --git a/tower-balance/Cargo.toml b/tower-balance/Cargo.toml
index 93d8bd5..8895ae7 100644
--- a/tower-balance/Cargo.toml
+++ b/tower-balance/Cargo.toml
@@ -21,5 +21,6 @@ hdrsample = "6.0"
 quickcheck = { version = "0.6", default-features = false }
 tokio = "0.1.7"
 tokio-executor = "0.1.2"
+tower = { version = "0.1", path = "../tower" }
 tower-buffer = { version = "0.1", path = "../tower-buffer" }
 tower-in-flight-limit = { version = "0.1", path = "../tower-in-flight-limit" }
diff --git a/tower-balance/examples/demo.rs b/tower-balance/examples/demo.rs
index 8b2f7f2..0e0b06d 100644
--- a/tower-balance/examples/demo.rs
+++ b/tower-balance/examples/demo.rs
@@ -1,31 +1,30 @@
 //! Exercises load balancers with mocked services.
 
 extern crate env_logger;
-#[macro_use]
 extern crate futures;
 extern crate hdrsample;
-#[macro_use]
 extern crate log;
 extern crate rand;
 extern crate tokio;
+extern crate tower;
 extern crate tower_balance;
 extern crate tower_buffer;
 extern crate tower_discover;
 extern crate tower_in_flight_limit;
 extern crate tower_service;
+extern crate tower_service_util;
 
-use futures::{future, stream, Async, Future, Poll, Stream};
+use futures::{future, stream, Future, Stream};
 use hdrsample::Histogram;
 use rand::Rng;
-use std::collections::VecDeque;
-use std::fmt;
 use std::time::{Duration, Instant};
 use tokio::{runtime, timer};
+use tower::ServiceExt;
 use tower_balance as lb;
-use tower_buffer::Buffer;
-use tower_discover::{Change, Discover};
+use tower_discover::Discover;
 use tower_in_flight_limit::InFlightLimit;
 use tower_service::Service;
+use tower_service_util::ServiceFn;
 
 const REQUESTS: usize = 50_000;
 const CONCURRENCY: usize = 50;
@@ -89,46 +88,64 @@ fn main() {
     rt.shutdown_on_idle().wait().unwrap();
 }
 
-fn gen_disco() -> Disco {
-    use self::Change::Insert;
+type Error = Box<::std::error::Error + Send + Sync>;
 
-    let mut changes = VecDeque::new();
-    for (i, latency) in MAX_ENDPOINT_LATENCIES.iter().enumerate() {
-        changes.push_back(Insert(i, DelayService(*latency)));
-    }
+fn gen_disco() -> impl Discover<
+    Key = usize,
+    Error = impl Into<Error>,
+    Service = impl Service<Req, Response = Rsp, Error = Error, Future = impl Send> + Send,
+> + Send {
+    tower_discover::ServiceList::new(MAX_ENDPOINT_LATENCIES.iter().map(|latency| {
+        let svc = ServiceFn::new(move |_| {
+            let start = Instant::now();
+            let maxms = u64::from(latency.subsec_nanos() / 1_000 / 1_000)
+                .saturating_add(latency.as_secs().saturating_mul(1_000));
+            let latency = Duration::from_millis(rand::thread_rng().gen_range(0, maxms));
+            let delay = timer::Delay::new(start + latency);
 
-    Disco { changes }
+            delay.map(move |_| {
+                let latency = Instant::now() - start;
+                Rsp { latency }
+            })
+        });
+
+        InFlightLimit::new(svc, ENDPOINT_CAPACITY)
+    }))
 }
 
 fn run<D, C>(name: &'static str, lb: lb::Balance<D, C>) -> impl Future<Item = (), Error = ()>
 where
     D: Discover + Send + 'static,
+    D::Error: Into<Error>,
     D::Key: Send,
-    D::Service: Service<Req, Response = Rsp> + Send,
-    D::Error: ::std::error::Error + Send + Sync + 'static,
+    D::Service: Service<Req, Response = Rsp, Error = Error> + Send,
     <D::Service as Service<Req>>::Future: Send,
-    <D::Service as Service<Req>>::Error: ::std::error::Error + Send + Sync + 'static,
     C: lb::Choose<D::Key, D::Service> + Send + 'static,
 {
     println!("{}", name);
     let t0 = Instant::now();
 
-    compute_histo(SendRequests::new(lb, REQUESTS, CONCURRENCY))
+    let requests = stream::repeat::<_, Error>(Req).take(REQUESTS as u64);
+    let service = InFlightLimit::new(lb, CONCURRENCY);
+    let responses = service.call_all(requests).unordered();
+
+    compute_histo(responses)
         .map(move |h| report(&h, t0.elapsed()))
         .map_err(|_| {})
 }
 
-fn compute_histo<S>(times: S) -> impl Future<Item = Histogram<u64>, Error = S::Error> + 'static
+fn compute_histo<S>(times: S) -> impl Future<Item = Histogram<u64>, Error = Error> + 'static
 where
-    S: Stream<Item = Rsp> + 'static,
+    S: Stream<Item = Rsp, Error = Error> + 'static,
 {
     // The max delay is 2000ms. At 3 significant figures.
     let histo = Histogram::<u64>::new_with_max(3_000, 3).unwrap();
+
     times.fold(histo, |mut histo, Rsp { latency }| {
         let ms = latency.as_secs() * 1_000;
         let ms = ms + u64::from(latency.subsec_nanos()) / 1_000 / 1_000;
         histo += ms;
-        future::ok(histo)
+        future::ok::<_, Error>(histo)
     })
 }
 
@@ -161,193 +178,10 @@ fn report(histo: &Histogram<u64>, elapsed: Duration) {
     println!("  p999 {:4}ms", histo.value_at_quantile(0.999));
 }
 
-#[derive(Debug)]
-struct DelayService(Duration);
-
-#[derive(Debug)]
-struct Delay {
-    delay: timer::Delay,
-    start: Instant,
-}
-
-struct Disco {
-    changes: VecDeque<Change<usize, DelayService>>,
-}
-
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 struct Req;
 
 #[derive(Debug)]
 struct Rsp {
     latency: Duration,
 }
-
-impl Service<Req> for DelayService {
-    type Response = Rsp;
-    type Error = timer::Error;
-    type Future = Delay;
-
-    fn poll_ready(&mut self) -> Poll<(), Self::Error> {
-        debug!("polling delay service: ready");
-        Ok(Async::Ready(()))
-    }
-
-    fn call(&mut self, _: Req) -> Delay {
-        let start = Instant::now();
-        let maxms = u64::from(self.0.subsec_nanos() / 1_000 / 1_000)
-            .saturating_add(self.0.as_secs().saturating_mul(1_000));
-        let latency = Duration::from_millis(rand::thread_rng().gen_range(0, maxms));
-        Delay {
-            delay: timer::Delay::new(start + latency),
-            start,
-        }
-    }
-}
-
-impl Future for Delay {
-    type Item = Rsp;
-    type Error = timer::Error;
-    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
-        try_ready!(self.delay.poll());
-        let rsp = Rsp {
-            latency: Instant::now() - self.start,
-        };
-        Ok(Async::Ready(rsp))
-    }
-}
-
-impl Discover for Disco {
-    type Key = usize;
-    type Error = DiscoError;
-    type Service = Errify<InFlightLimit<Buffer<DelayService, Req>>>;
-
-    fn poll(&mut self) -> Poll<Change<Self::Key, Self::Service>, Self::Error> {
-        match self.changes.pop_front() {
-            Some(Change::Insert(k, svc)) => {
-                let svc = Buffer::new(svc, 0).unwrap();
-                let svc = Errify(InFlightLimit::new(svc, ENDPOINT_CAPACITY));
-                Ok(Async::Ready(Change::Insert(k, svc)))
-            }
-            Some(Change::Remove(k)) => Ok(Async::Ready(Change::Remove(k))),
-            None => Ok(Async::NotReady),
-        }
-    }
-}
-
-#[derive(Debug)]
-pub struct DiscoError;
-
-impl fmt::Display for DiscoError {
-    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-        write!(fmt, "discovery error")
-    }
-}
-
-impl std::error::Error for DiscoError {}
-
-type DemoService<D, C> = InFlightLimit<Buffer<lb::Balance<D, C>, Req>>;
-
-struct SendRequests<D, C>
-where
-    D: Discover,
-    D::Error: ::std::error::Error + Send + Sync + 'static,
-    D::Service: Service<Req>,
-    <D::Service as Service<Req>>::Error: ::std::error::Error + Send + Sync + 'static,
-    C: lb::Choose<D::Key, D::Service>,
-{
-    send_remaining: usize,
-    lb: DemoService<D, C>,
-    responses: stream::FuturesUnordered<<DemoService<D, C> as Service<Req>>::Future>,
-}
-
-impl<D, C> SendRequests<D, C>
-where
-    D: Discover + Send + 'static,
-    D::Error: ::std::error::Error + Send + Sync + 'static,
-    D::Service: Service<Req>,
-    <D::Service as Service<Req>>::Error: ::std::error::Error + Send + Sync + 'static,
-    D::Key: Send,
-    D::Service: Send,
-    D::Error: Send + Sync,
-    <D::Service as Service<Req>>::Future: Send,
-    <D::Service as Service<Req>>::Error: Send + Sync,
-    C: lb::Choose<D::Key, D::Service> + Send + 'static,
-{
-    pub fn new(lb: lb::Balance<D, C>, total: usize, concurrency: usize) -> Self {
-        Self {
-            send_remaining: total,
-            lb: InFlightLimit::new(Buffer::new(lb, 0).ok().expect("buffer"), concurrency),
-            responses: stream::FuturesUnordered::new(),
-        }
-    }
-}
-
-impl<D, C> Stream for SendRequests<D, C>
-where
-    D: Discover,
-    D::Error: ::std::error::Error + Send + Sync + 'static,
-    D::Service: Service<Req>,
-    <D::Service as Service<Req>>::Error: ::std::error::Error + Send + Sync + 'static,
-    C: lb::Choose<D::Key, D::Service>,
-{
-    type Item = <DemoService<D, C> as Service<Req>>::Response;
-    type Error = <DemoService<D, C> as Service<Req>>::Error;
-
-    fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
-        debug!(
-            "sending requests {} / {}",
-            self.send_remaining,
-            self.responses.len()
-        );
-        while self.send_remaining > 0 {
-            if !self.responses.is_empty() {
-                if let Async::Ready(Some(rsp)) = self.responses.poll()? {
-                    return Ok(Async::Ready(Some(rsp)));
-                }
-            }
-
-            debug!("polling lb ready");
-            try_ready!(self.lb.poll_ready());
-
-            debug!("sending request");
-            let rsp = self.lb.call(Req);
-            self.responses.push(rsp);
-
-            self.send_remaining -= 1;
-        }
-
-        if !self.responses.is_empty() {
-            return self.responses.poll();
-        }
-
-        Ok(Async::Ready(None))
-    }
-}
-
-pub struct Errify<T>(T);
-
-impl<T, Request> Service<Request> for Errify<T>
-where
-    T: Service<Request>,
-{
-    type Response = T::Response;
-    type Error = DiscoError;
-    type Future = Errify<T::Future>;
-
-    fn poll_ready(&mut self) -> Poll<(), Self::Error> {
-        self.0.poll_ready().map_err(|_| DiscoError)
-    }
-
-    fn call(&mut self, request: Request) -> Self::Future {
-        Errify(self.0.call(request))
-    }
-}
-
-impl<T: Future> Future for Errify<T> {
-    type Item = T::Item;
-    type Error = DiscoError;
-
-    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
-        self.0.poll().map_err(|_| DiscoError)
-    }
-}