From 759556d9313484c0678a82eaf452dd7e4a9eecdb Mon Sep 17 00:00:00 2001
From: "Stephen M. Coakley" <me@stephencoakley.com>
Date: Wed, 22 May 2019 22:25:48 -0500
Subject: [PATCH] micro-optimization: reuse same cursor over and over

---
 benches/pipe.rs     | 55 ++++++++++++++++++++++-----------------------
 src/pipe/chunked.rs | 18 +++++++--------
 2 files changed, 36 insertions(+), 37 deletions(-)

diff --git a/benches/pipe.rs b/benches/pipe.rs
index 89dbb3f..2dffb0e 100644
--- a/benches/pipe.rs
+++ b/benches/pipe.rs
@@ -1,37 +1,36 @@
 #![feature(async_await)]
 
-#[macro_use]
-extern crate criterion;
+use criterion::*;
 
-use criterion::Criterion;
-use futures::executor::ThreadPool;
-use futures::prelude::*;
-use std::io;
+fn benchmark(c: &mut Criterion) {
+    c.bench_function("write 100 1K chunks", |b| {
+        use futures::executor::ThreadPool;
+        use futures::prelude::*;
 
-fn criterion_benchmark(c: &mut Criterion) {
-    c.bench_function("pipe_read_write", |b| {
         let mut pool = ThreadPool::new().unwrap();
-        let data = [1; 0x1000];
-
-        b.iter(|| {
-            let (mut reader, mut writer) = sluice::pipe::pipe();
-
-            let producer = async {
-                for _ in 0..0x10 {
-                    writer.write_all(&data).await.unwrap();
-                }
-                writer.close().await.unwrap();
-            };
-
-            let consumer = async {
-                let mut sink = io::sink();
-                reader.copy_into(&mut sink).await.unwrap();
-            };
-
-            pool.run(future::join(producer, consumer));
-        })
+        let data = [1; 1024];
+
+        b.iter_batched(
+            sluice::pipe::pipe,
+            |(mut reader, mut writer)| {
+                let producer = async {
+                    for _ in 0..100 {
+                        writer.write_all(&data).await.unwrap();
+                    }
+                    writer.close().await.unwrap();
+                };
+
+                let consumer = async {
+                    let mut sink = std::io::sink();
+                    reader.copy_into(&mut sink).await.unwrap();
+                };
+
+                pool.run(future::join(producer, consumer));
+            },
+            BatchSize::SmallInput,
+        )
     });
 }
 
-criterion_group!(benches, criterion_benchmark);
+criterion_group!(benches, benchmark);
 criterion_main!(benches);
diff --git a/src/pipe/chunked.rs b/src/pipe/chunked.rs
index 6af9214..c0ed1ad 100644
--- a/src/pipe/chunked.rs
+++ b/src/pipe/chunked.rs
@@ -44,7 +44,7 @@ pub fn new(count: usize) -> (Reader, Writer) {
 
     // Fill up the buffer pool.
     for _ in 0..count {
-        buf_pool_tx.try_send(Vec::new()).expect("buffer pool overflow");
+        buf_pool_tx.try_send(Cursor::new(Vec::new())).expect("buffer pool overflow");
     }
 
     let reader = Reader {
@@ -64,10 +64,10 @@ pub fn new(count: usize) -> (Reader, Writer) {
 /// The reading half of a chunked pipe.
 pub struct Reader {
     /// A channel of incoming chunks from the writer.
-    buf_pool_tx: mpsc::Sender<Vec<u8>>,
+    buf_pool_tx: mpsc::Sender<Cursor<Vec<u8>>>,
 
     /// A channel of chunk buffers that have been consumed and can be reused.
-    buf_stream_rx: mpsc::Receiver<Vec<u8>>,
+    buf_stream_rx: mpsc::Receiver<Cursor<Vec<u8>>>,
 
     /// A chunk currently being read from.
     chunk: Option<Cursor<Vec<u8>>>,
@@ -88,7 +88,7 @@ impl AsyncRead for Reader {
                 Poll::Ready(None) => return Poll::Ready(Ok(0)),
 
                 // Accept the new chunk.
-                Poll::Ready(Some(buf)) => Cursor::new(buf),
+                Poll::Ready(Some(buf)) => buf,
             }
         };
 
@@ -106,8 +106,8 @@ impl AsyncRead for Reader {
 
         // Otherwise, return it to the writer to be reused.
         else {
-            let mut chunk = chunk.into_inner();
-            chunk.clear();
+            chunk.set_position(0);
+            chunk.get_mut().clear();
 
             match self.buf_pool_tx.try_send(chunk) {
                 Ok(()) => {}
@@ -131,10 +131,10 @@ impl AsyncRead for Reader {
 /// Writing half of a chunked pipe.
 pub struct Writer {
     /// A channel of chunks to send to the reader.
-    buf_pool_rx: mpsc::Receiver<Vec<u8>>,
+    buf_pool_rx: mpsc::Receiver<Cursor<Vec<u8>>>,
 
     /// A channel of incoming buffers to write chunks to.
-    buf_stream_tx: mpsc::Sender<Vec<u8>>,
+    buf_stream_tx: mpsc::Sender<Cursor<Vec<u8>>>,
 }
 
 impl AsyncWrite for Writer {
@@ -150,7 +150,7 @@ impl AsyncWrite for Writer {
             // An available buffer has been found.
             Poll::Ready(Some(mut chunk)) => {
                 // Write the buffer to the chunk.
-                chunk.extend_from_slice(buf);
+                chunk.get_mut().extend_from_slice(buf);
 
                 // Send the chunk to the reader.
                 match self.buf_stream_tx.try_send(chunk) {