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Improve Http2Pool connection reuse for concurrent acquires #4051

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19a4547
Improve Http2Pool connection reuse for concurrent acquires
zimatars Jan 6, 2026
20b048f
Improve Http2Pool connection reuse for concurrent acquires
zimatars Jan 25, 2026
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12 changes: 7 additions & 5 deletions reactor-netty-http/src/main/java/reactor/netty/http/client/Http2Pool.java
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Original file line number Diff line number Diff line change
Expand Up @@ -391,7 +391,8 @@ void drainLoop() {
// when cached connections are below minimum connections, then allocate a new connection
boolean belowMinConnections = minConnections > 0 &&
poolConfig.allocationStrategy().permitGranted() < minConnections;
Slot slot = belowMinConnections ? null : findConnection(resources);
int resourcesCount = idleSize;
Slot slot = belowMinConnections ? null : findConnection(resources, resourcesCount);
if (slot != null) {
Borrower borrower = pollPending(borrowers, true);
if (borrower == null || borrower.get()) {
Expand All @@ -412,10 +413,12 @@ void drainLoop() {
});
}
else {
int resourcesCount = idleSize;
if (minConnections > 0 &&
poolConfig.allocationStrategy().permitGranted() >= minConnections &&
resourcesCount == 0) {
poolConfig.allocationStrategy().permitGranted() > resourcesCount) {
// connections allocations were triggered
}
else if (minConnections == 0 && poolConfig.allocationStrategy().permitGranted() > resourcesCount) {
// connections allocations were triggered
}
else {
Expand Down Expand Up @@ -539,8 +542,7 @@ void evictInBackground() {
scheduleEviction();
}

@Nullable Slot findConnection(ConcurrentLinkedQueue<Slot> resources) {
int resourcesCount = idleSize;
@Nullable Slot findConnection(ConcurrentLinkedQueue<Slot> resources, int resourcesCount) {
while (resourcesCount > 0) {
// There are connections in the queue

Expand Down
54 changes: 53 additions & 1 deletion reactor-netty-http/src/test/java/reactor/netty/http/client/Http2PoolTest.java
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2021-2025 VMware, Inc. or its affiliates, All Rights Reserved.
* Copyright (c) 2021-2026 VMware, Inc. or its affiliates, All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
Expand Down Expand Up @@ -144,6 +144,58 @@ void acquireRelease() {
}
}

@Test
void concurrentAcquireReusesConnection() {
AtomicInteger allocator = new AtomicInteger();
ConcurrentLinkedQueue<EmbeddedChannel> channels = new ConcurrentLinkedQueue<>();

PoolBuilder<Connection, PoolConfig<Connection>> poolBuilder =
PoolBuilder.from(Mono.fromSupplier(() -> {
allocator.incrementAndGet();
EmbeddedChannel channel = new EmbeddedChannel(
new TestChannelId(),
Http2FrameCodecBuilder.forClient().build(),
new Http2MultiplexHandler(new ChannelHandlerAdapter() {}));
channels.add(channel);
return Connection.from(channel);
}))
.idleResourceReuseLruOrder()
.maxPendingAcquireUnbounded()
.sizeBetween(0, 2);
Http2Pool http2Pool = poolBuilder.build(config -> new Http2Pool(config, null));

List<PooledRef<Connection>> acquired = new ArrayList<>();
try {
// Warm-up: allocate a connection and cache it.
PooledRef<Connection> warm = http2Pool.acquire().block(Duration.ofSeconds(1));
assertThat(warm).isNotNull();
warm.release().block(Duration.ofSeconds(1));

// Don't run pending tasks yet, simulate concurrent acquires before deliver is scheduled.
http2Pool.acquire().subscribe(acquired::add);
http2Pool.acquire().subscribe(acquired::add);

assertThat(allocator).as("allocator count").hasValue(1);

channels.forEach(EmbeddedChannel::runPendingTasks);

assertThat(acquired).hasSize(2);
assertThat(acquired.get(0).poolable())
.as("both acquires should share the same H2 connection")
.isSameAs(acquired.get(1).poolable());

for (PooledRef<Connection> ref : acquired) {
ref.release().block(Duration.ofSeconds(1));
}
}
finally {
for (EmbeddedChannel channel : channels) {
channel.finishAndReleaseAll();
Connection.from(channel).dispose();
}
}
}

@Test
void doAcquireNotCalledIfBorrowerInScopeCancelledEarly() {
AtomicInteger allocator = new AtomicInteger();
Expand Down
17 changes: 11 additions & 6 deletions ...c/test/java/reactor/netty/http/client/Http2PooledConnectionProviderCustomMetricsTest.java
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2025 VMware, Inc. or its affiliates, All Rights Reserved.
* Copyright (c) 2026 VMware, Inc. or its affiliates, All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
Expand Down Expand Up @@ -42,6 +42,7 @@

import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
import static org.awaitility.Awaitility.await;
import static reactor.netty.http.HttpProtocol.H2;

class Http2PooledConnectionProviderCustomMetricsTest extends BaseHttpTest {
Expand Down Expand Up @@ -78,7 +79,7 @@ void measureActiveStreamsSize() throws InterruptedException {
.maxConnections(10)
.build();

CountDownLatch latch = new CountDownLatch(5);
CountDownLatch latch = new CountDownLatch(1);
HttpClient httpClient =
createClient(pool, disposableServer::address)
.protocol(H2)
Expand All @@ -94,10 +95,14 @@ void measureActiveStreamsSize() throws InterruptedException {
.subscribe());

assertThat(latch.await(5, TimeUnit.SECONDS)).isTrue();
assertThat(isRegistered.get()).isTrue();
HttpConnectionPoolMetrics actual = metrics.get();
assertThat(actual).isNotNull();
assertThat(actual.activeStreamSize()).isEqualTo(5);

await().atMost(5, TimeUnit.SECONDS)
.untilAsserted(() -> {
assertThat(isRegistered.get()).isTrue();
HttpConnectionPoolMetrics actual = metrics.get();
assertThat(actual).isNotNull();
assertThat(actual.activeStreamSize()).isEqualTo(5);
});
}
finally {
pool.disposeLater().block(Duration.ofSeconds(5));
Expand Down
8 changes: 5 additions & 3 deletions reactor-netty-http/src/test/java/reactor/netty/http/server/HttpServerTests.java
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2011-2025 VMware, Inc. or its affiliates, All Rights Reserved.
* Copyright (c) 2011-2026 VMware, Inc. or its affiliates, All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
Expand Down Expand Up @@ -1854,7 +1854,9 @@ void testGracefulShutdownH2(HttpProtocol[] serverProtocols, HttpProtocol[] clien
private void doTestGracefulShutdown(HttpServer server, HttpClient client) throws Exception {
CountDownLatch latch1 = new CountDownLatch(2);
CountDownLatch latch2 = new CountDownLatch(2);
CountDownLatch latchGoAway = new CountDownLatch(2);
// HTTP/2 GOAWAY is a connection-level frame. With multiplexing enabled, both concurrent requests
// can share the same connection, so we should only expect at least one GOAWAY to be observed.
CountDownLatch latchGoAway = new CountDownLatch(1);
CountDownLatch latch3 = new CountDownLatch(1);
LoopResources loop = LoopResources.create("testGracefulShutdown");
group = new DefaultChannelGroup(executor);
Expand Down Expand Up @@ -1906,7 +1908,7 @@ public void channelRead(@NotNull ChannelHandlerContext ctx, @NotNull Object msg)
// Stop accepting incoming requests, wait at most 3s for the active requests to finish
disposableServer.disposeNow();

assertThat(latchGoAway.await(30, TimeUnit.SECONDS)).as("2 GOAWAY should have been received").isTrue();
assertThat(latchGoAway.await(30, TimeUnit.SECONDS)).as("GOAWAY should have been received").isTrue();
assertThat(latch2.await(30, TimeUnit.SECONDS)).isTrue();

// Dispose the event loop
Expand Down