From 1c463da9974575711b032d57988c62724facb395 Mon Sep 17 00:00:00 2001
From: Scott Mitchell <scott_mitchell@apple.com>
Date: Tue, 4 Oct 2022 12:11:21 -0700
Subject: [PATCH] PublisherAsBlockingIterable LinkedBlockingQueue ->
 LinkedTransferQueue (#2386)

Motivation:
LinkedBlockingQueue goes through LockSupport park and unpark methods
which can incur relatively expensive context switching if the EventLoop
thread has to unpark an application thread. This has been shown to be
a bottleneck as throughput increases.

Modifications:
- Use LinkedTransferQueue which does a `Thread.yield()` before parking
  on the consumer thread. This may use more CPU on the consumer thread
  but the assumption is there will be many more application threads than
  EventLoop threads and we want to minimize producer costs.

Results:

LinkedTransferQueue
```
Running 30s test @ http://localhost:8080/medium, using 'ServiceTalkGrpcBlockingClientStrAgg' client
  1024 threads and 1024 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency       -          -       -           -
    Req/Sec     0.01k        -     0.01k         -
  290977 requests in 30s
Requests/sec: 9699.23
Transfer/sec: -
OK: 290977
KO: 0
```

LinkedBlockingQueue
```
Running 30s test @ http://localhost:8080/medium, using 'ServiceTalkGrpcBlockingClientStrAgg' client
  1024 threads and 1024 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency       -          -       -           -
    Req/Sec     0.01k        -     0.01k         -
  256778 requests in 30s
Requests/sec: 8559.27
Transfer/sec: -
OK: 256778
KO: 0
```
---
 .../concurrent/api/PublisherAsBlockingIterable.java         | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/servicetalk-concurrent-api/src/main/java/io/servicetalk/concurrent/api/PublisherAsBlockingIterable.java b/servicetalk-concurrent-api/src/main/java/io/servicetalk/concurrent/api/PublisherAsBlockingIterable.java
index 229470f018..d35b53cead 100644
--- a/servicetalk-concurrent-api/src/main/java/io/servicetalk/concurrent/api/PublisherAsBlockingIterable.java
+++ b/servicetalk-concurrent-api/src/main/java/io/servicetalk/concurrent/api/PublisherAsBlockingIterable.java
@@ -30,7 +30,7 @@
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 import java.util.concurrent.BlockingQueue;
-import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.LinkedTransferQueue;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 import javax.annotation.Nullable;
@@ -39,7 +39,7 @@
 import static io.servicetalk.concurrent.api.SubscriberApiUtils.wrapNull;
 import static io.servicetalk.concurrent.internal.TerminalNotification.complete;
 import static io.servicetalk.concurrent.internal.TerminalNotification.error;
-import static io.servicetalk.utils.internal.PlatformDependent.throwException;
+import static io.servicetalk.utils.internal.ThrowableUtils.throwException;
 import static java.lang.Math.min;
 import static java.lang.Thread.currentThread;
 import static java.util.Objects.requireNonNull;
@@ -101,7 +101,7 @@ private static final class SubscriberAndIterator<T> implements Subscriber<T>, Bl
 
         SubscriberAndIterator(int queueCapacity) {
             requestN = queueCapacity;
-            data = new LinkedBlockingQueue<>();
+            data = new LinkedTransferQueue<>();
         }
 
         @Override