From 3d69a8b7d0d653457096e9b95a6138ff5691386c Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Thu, 10 Nov 2016 20:10:02 -0800
Subject: Add a benchmark for futures channel latency

---
 benches/latency.rs | 38 +++++++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 7 deletions(-)

diff --git a/benches/latency.rs b/benches/latency.rs
index 5b73d44a..4dfc708a 100644
--- a/benches/latency.rs
+++ b/benches/latency.rs
@@ -7,16 +7,15 @@ extern crate tokio_core;
 
 use std::io;
 use std::net::SocketAddr;
+use std::thread;
 
+use futures::sync::oneshot;
+use futures::sync::spsc;
 use futures::{Future, Poll, Sink, Stream};
+use test::Bencher;
+use tokio_core::channel::Sender;
 use tokio_core::net::UdpSocket;
 use tokio_core::reactor::Core;
-use tokio_core::channel::Sender;
-
-use test::Bencher;
-use std::thread;
-
-use futures::sync::oneshot;
 
 /// UDP echo server
 struct EchoServer {
@@ -96,7 +95,7 @@ fn udp_echo_latency(b: &mut Bencher) {
 }
 
 #[bench]
-fn channel_latency(b: &mut Bencher) {
+fn tokio_channel_latency(b: &mut Bencher) {
     let (tx, rx) = oneshot::channel();
 
     let child = thread::spawn(move || {
@@ -131,3 +130,28 @@ fn channel_latency(b: &mut Bencher) {
     drop(in_tx);
     child.join().unwrap();
 }
+
+#[bench]
+fn futures_channel_latency(b: &mut Bencher) {
+    let (mut in_tx, in_rx) = spsc::channel();
+    let (out_tx, out_rx) = spsc::channel::<_, ()>();
+
+    let child = thread::spawn(|| out_tx.send_all(in_rx).wait());
+    let mut rx_iter = out_rx.wait();
+
+    // warmup phase; for some reason initial couple of runs are much slower
+    //
+    // TODO: Describe the exact reasons; caching? branch predictor? lazy closures?
+    for _ in 0..8 {
+        in_tx.start_send(Ok(Ok(1usize))).unwrap();
+        let _ = rx_iter.next();
+    }
+
+    b.iter(|| {
+        in_tx.start_send(Ok(Ok(1usize))).unwrap();
+        let _ = rx_iter.next();
+    });
+
+    drop(in_tx);
+    child.join().unwrap().unwrap();
+}
-- 
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