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DataBufferUtils.write() with NettyDataBuffer on JDK 25 hangs indefinitely #36184

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DataBufferUtils.write() with NettyDataBuffer on JDK 25 hangs indefinitely#36184
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rstoyanchev
Labels
in: coreIssues in core modules (aop, beans, core, context, expression)status: backportedAn issue that has been backported to maintenance branchestype: enhancementA general enhancement
Milestone
7.0.4
@kzander91

Description

@kzander91
kzander91
opened on Jan 20, 2026

Spring Framework: 7.0.3

In the following snippet, (on Windows) and JDK 25, handling the request hangs forever in DataBufferUtils.write():

@RestController
@SpringBootApplication
public class Demo21Application {

    public static void main(String[] args) {
        SpringApplication.run(Demo21Application.class, args);
    }

    @GetMapping("/")
    Mono<Void> get(ServerWebExchange exchange) {
        DataBufferFactory bf = exchange.getResponse().bufferFactory();
        DataBuffer buf = bf.allocateBuffer(64);
        buf.write("hello world", StandardCharsets.UTF_8);
        return DataBufferUtils.write(Mono.just(buf), Path.of("out.txt"));
    }

}

Running the same on Java 21 succeeds.

The issue is that an exception is thrown in this line (writing is true at this point):

spring-framework/spring-core/src/main/java/org/springframework/core/io/buffer/DataBufferUtils.java

Line 1208 in 02cdd36

this.channel.write(byteBuffer, pos, attachment, this);

The exception is caught by reactor and given into hookOnError here:

spring-framework/spring-core/src/main/java/org/springframework/core/io/buffer/DataBufferUtils.java

Lines 1213 to 1219 in 02cdd36

protected void hookOnError(Throwable throwable) {
this.error.set(throwable);
if (!this.writing.get()) {
this.sink.error(throwable);
}
}

But since writing is still true, the exception is swallowed and sink never terminates.

The underlying root cause seems to be an issue with Netty and/or Java (see netty/netty#15324), but the exception handling in WriteCompletionHandler is insufficient.

The exception:
Image
Stack trace:

java.lang.UnsupportedOperationException: ByteBuffer derived from closeable shared sessions not supported
	at java.base/java.nio.DirectByteBuffer.address(DirectByteBuffer.java:319)
	at java.base/sun.nio.ch.WindowsAsynchronousFileChannelImpl$WriteTask.run(WindowsAsynchronousFileChannelImpl.java:629)
	at java.base/sun.nio.ch.WindowsAsynchronousFileChannelImpl.implWrite(WindowsAsynchronousFileChannelImpl.java:745)
	at java.base/sun.nio.ch.AsynchronousFileChannelImpl.write(AsynchronousFileChannelImpl.java:251)
	at org.springframework.core.io.buffer.DataBufferUtils$WriteCompletionHandler.hookOnNext(DataBufferUtils.java:1208)
	at org.springframework.core.io.buffer.DataBufferUtils$WriteCompletionHandler.hookOnNext(DataBufferUtils.java:1172)
	at reactor.core.publisher.BaseSubscriber.onNext(BaseSubscriber.java:164)
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2565)
	at reactor.core.publisher.BaseSubscriber.request(BaseSubscriber.java:218)
	at org.springframework.core.io.buffer.DataBufferUtils$WriteCompletionHandler.hookOnSubscribe(DataBufferUtils.java:1197)
	at reactor.core.publisher.BaseSubscriber.onSubscribe(BaseSubscriber.java:152)
	at reactor.core.publisher.FluxJust.subscribe(FluxJust.java:69)
	at org.springframework.core.io.buffer.DataBufferUtils.lambda$write$1(DataBufferUtils.java:340)
	at reactor.core.publisher.FluxCreate.subscribe(FluxCreate.java:97)
	at reactor.core.publisher.Flux.subscribe(Flux.java:8888)
	at reactor.core.publisher.Flux.subscribeWith(Flux.java:9009)
	at reactor.core.publisher.Flux.subscribe(Flux.java:8853)
	at org.springframework.core.io.buffer.DataBufferUtils.lambda$write$2(DataBufferUtils.java:369)
	at reactor.core.publisher.MonoCreate.subscribe(MonoCreate.java:61)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:166)
	at reactor.core.publisher.MonoZip$ZipCoordinator.signal(MonoZip.java:296)
	at reactor.core.publisher.MonoZip$ZipInner.onNext(MonoZip.java:480)
	at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onNext(MonoPeekTerminal.java:184)
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2565)
	at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.request(MonoPeekTerminal.java:142)
	at reactor.core.publisher.MonoZip$ZipInner.onSubscribe(MonoZip.java:472)
	at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onSubscribe(MonoPeekTerminal.java:155)
	at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:56)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
	at reactor.core.publisher.MonoZip$ZipCoordinator.request(MonoZip.java:219)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.request(MonoFlatMap.java:195)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onSubscribe(MonoIgnoreThen.java:135)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onSubscribe(MonoFlatMap.java:118)
	at reactor.core.publisher.MonoZip.subscribe(MonoZip.java:129)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:54)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:244)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:207)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onComplete(MonoFlatMap.java:190)
	at reactor.core.publisher.Operators.complete(Operators.java:137)
	at reactor.core.publisher.MonoZip.subscribe(MonoZip.java:121)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4569)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:268)
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:166)
	at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onNext(FluxOnErrorResume.java:80)
	at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:75)
	at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:83)
	at reactor.core.publisher.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.innerNext(FluxConcatMapNoPrefetch.java:259)
	at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onNext(FluxConcatMap.java:870)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.secondComplete(MonoFlatMap.java:246)
	at reactor.core.publisher.MonoFlatMap$FlatMapInner.onNext(MonoFlatMap.java:307)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:130)
	at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onNext(MonoPeekTerminal.java:184)
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2565)
	at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.request(MonoPeekTerminal.java:142)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:172)
	at reactor.core.publisher.MonoFlatMap$FlatMapInner.onSubscribe(MonoFlatMap.java:293)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:96)
	at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onSubscribe(MonoPeekTerminal.java:155)
	at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:56)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:166)
	at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onNext(FluxPeekFuseable.java:211)
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2565)
	at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.request(FluxPeekFuseable.java:144)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.request(MonoFlatMap.java:195)
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.set(Operators.java:2361)
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onSubscribe(Operators.java:2235)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onSubscribe(MonoFlatMap.java:118)
	at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onSubscribe(FluxPeekFuseable.java:178)
	at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:56)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4569)
	at reactor.core.publisher.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.onNext(FluxConcatMapNoPrefetch.java:207)
	at reactor.core.publisher.FluxIterable$IterableSubscription.slowPath(FluxIterable.java:335)
	at reactor.core.publisher.FluxIterable$IterableSubscription.request(FluxIterable.java:294)
	at reactor.core.publisher.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.innerComplete(FluxConcatMapNoPrefetch.java:275)
	at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onComplete(FluxConcatMap.java:894)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.secondComplete(MonoFlatMap.java:251)
	at reactor.core.publisher.MonoFlatMap$FlatMapInner.onComplete(MonoFlatMap.java:326)
	at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:144)
	at reactor.core.publisher.Operators.complete(Operators.java:137)
	at reactor.core.publisher.MonoEmpty.subscribe(MonoEmpty.java:46)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:166)
	at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onNext(FluxPeekFuseable.java:211)
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2565)
	at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.request(FluxPeekFuseable.java:144)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.request(MonoFlatMap.java:195)
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.request(Operators.java:2325)
	at reactor.core.publisher.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.request(FluxConcatMapNoPrefetch.java:339)
	at reactor.core.publisher.MonoNext$NextSubscriber.request(MonoNext.java:109)
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.set(Operators.java:2361)
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onSubscribe(Operators.java:2235)
	at reactor.core.publisher.MonoNext$NextSubscriber.onSubscribe(MonoNext.java:71)
	at reactor.core.publisher.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.onSubscribe(FluxConcatMapNoPrefetch.java:164)
	at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:200)
	at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:82)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:54)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4569)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:268)
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:75)
	at reactor.core.publisher.MonoDeferContextual.subscribe(MonoDeferContextual.java:56)
	at reactor.netty.http.server.HttpServer$HttpServerHandle.onStateChange(HttpServer.java:1344)
	at reactor.netty.ReactorNetty$CompositeConnectionObserver.onStateChange(ReactorNetty.java:730)
	at reactor.netty.transport.ServerTransport$ChildObserver.onStateChange(ServerTransport.java:489)
	at reactor.netty.http.server.HttpServerOperations.handleDefaultHttpRequest(HttpServerOperations.java:863)
	at reactor.netty.http.server.HttpServerOperations.onInboundNext(HttpServerOperations.java:789)
	at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:115)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:356)
	at reactor.netty.http.server.HttpTrafficHandler.channelRead(HttpTrafficHandler.java:283)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:354)
	at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:434)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:361)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:325)
	at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:249)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:354)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1429)
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:918)
	at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:172)
	at io.netty.channel.nio.AbstractNioChannel$AbstractNioUnsafe.handle(AbstractNioChannel.java:445)
	at io.netty.channel.nio.NioIoHandler$DefaultNioRegistration.handle(NioIoHandler.java:388)
	at io.netty.channel.nio.NioIoHandler.processSelectedKey(NioIoHandler.java:596)
	at io.netty.channel.nio.NioIoHandler.processSelectedKeysPlain(NioIoHandler.java:541)
	at io.netty.channel.nio.NioIoHandler.processSelectedKeys(NioIoHandler.java:514)
	at io.netty.channel.nio.NioIoHandler.run(NioIoHandler.java:484)
	at io.netty.channel.SingleThreadIoEventLoop.runIo(SingleThreadIoEventLoop.java:225)
	at io.netty.channel.SingleThreadIoEventLoop.run(SingleThreadIoEventLoop.java:196)
	at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:1195)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Thread.java:1474)

Here's a reproducer with a test that succeeds on Java 21 and fails on Java 25: demo21.zip

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in: coreIssues in core modules (aop, beans, core, context, expression)status: backportedAn issue that has been backported to maintenance branchestype: enhancementA general enhancement

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