Java 11 HttpClient Http2 流太多错误

Question

我正在使用 Java 11 的 HttpClient 将请求发布到 HTTP2 服务器。 HttpClient 对象被创建为 Singleton Spring bean，如下所示。

@Bean
    public HttpClient getClient() {
                return HttpClient.newBuilder().version(Version.HTTP_2).executor(Executors.newFixedThreadPool(20)).followRedirects(Redirect.NORMAL)
                .connectTimeout(Duration.ofSeconds(20)).build();
    }

I am using the sendAsync method to send the requests asynchronously.

When I try to hit the server continuously, I am receiving the error after certain time "java.io.IOException: too many concurrent streams". I used Fixed threadpool in the Client building to try to overcome this error, but it is still giving the same error.

The Exception stack is..

java.util.concurrent.CompletionException: java.io.IOException: too many concurrent streams
    at java.base/java.util.concurrent.CompletableFuture.encodeRelay(CompletableFuture.java:367) ~[?:?]
    at java.base/java.util.concurrent.CompletableFuture.uniComposeStage(CompletableFuture.java:1108) ~[?:?]
    at java.base/java.util.concurrent.CompletableFuture.thenCompose(CompletableFuture.java:2235) ~[?:?]
    at java.net.http/jdk.internal.net.http.MultiExchange.responseAsyncImpl(MultiExchange.java:345) ~[java.net.http:?]
    at java.net.http/jdk.internal.net.http.MultiExchange.lambda$responseAsync0$2(MultiExchange.java:250) ~[java.net.http:?]
    at java.base/java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:1072) ~[?:?]
    at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:506) ~[?:?]
    at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1705) ~[?:?]
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
    at java.base/java.lang.Thread.run(Thread.java:834) [?:?]
Caused by: java.io.IOException: too many concurrent streams
    at java.net.http/jdk.internal.net.http.Http2Connection.reserveStream(Http2Connection.java:440) ~[java.net.http:?]
    at java.net.http/jdk.internal.net.http.Http2ClientImpl.getConnectionFor(Http2ClientImpl.java:103) ~[java.net.http:?]
    at java.net.http/jdk.internal.net.http.ExchangeImpl.get(ExchangeImpl.java:88) ~[java.net.http:?]
    at java.net.http/jdk.internal.net.http.Exchange.establishExchange(Exchange.java:293) ~[java.net.http:?]
    at java.net.http/jdk.internal.net.http.Exchange.responseAsyncImpl0(Exchange.java:425) ~[java.net.http:?]
    at java.net.http/jdk.internal.net.http.Exchange.responseAsyncImpl(Exchange.java:330) ~[java.net.http:?]
    at java.net.http/jdk.internal.net.http.Exchange.responseAsync(Exchange.java:322) ~[java.net.http:?]
    at java.net.http/jdk.internal.net.http.MultiExchange.responseAsyncImpl(MultiExchange.java:304) ~[java.net.http:?]

有人可以帮我解决这个问题吗？

服务器是Tomcat9，它的最大并发流是默认的。

Answer 1

不幸的是，@sbordet 建议的Semaphore 方法对我不起作用。我试过这个：

var semaphore = semaphores.computeIfAbsent(getRequestKey(request), k -> new Semaphore(MAX_CONCURRENT_REQUESTS_NUMBER));

CompletableFuture.runAsync(semaphore::acquireUninterruptibly, WAITING_POOL)
                .thenComposeAsync(ignored -> httpClient.sendAsync(request, responseBodyHandler), ASYNC_POOL)
                .whenComplete((response, e) -> semaphore.release());

无法保证在将执行传递到下一个CompletableFuture（释放信号量）时释放连接流。对我来说，该方法在正常执行的情况下有效，但是如果有任何异常，似乎在调用semaphore.release() 后连接流可能会关闭。

最后，我最终使用了OkHttp。它处理这个问题（如果并发流的数量达到max_concurrent_streams，它只是等到一些流被释放）。它还处理GOAWAY 帧。在 Java HttpClient 的情况下，我必须实现重试逻辑来处理这个问题，因为如果服务器发送 GOAWAY 帧，它只会抛出 IOException。

Answer 2

当我尝试连续访问服务器时

服务器有一个max_concurrent_streams 的设置，在 HTTP/2 连接的初始建立期间与客户端通信。

如果您使用sendAsync 盲目地“连续访问服务器”，则您不会等待先前的请求完成，最终您会超过max_concurrent_streams 的值并收到上述错误。

解决办法是并发发送多个小于max_concurrent_streams的请求；之后，您只会在前一个请求完成时发送一个新请求。 这可以使用Semaphore 或类似的东西在客户端上轻松实现。