线上使用 CompletableFuture.supplyAsync 来多线程下载影像，使用了默认的ForkJoinPool线程池。
项目运行一段时间后下载影像方法全部报错：
java.util.concurrent.TimeoutException
下载方法如下：
public File download(String url, String filename) throws IOException {
File file = new File(parent, filename);
try (CloseableHttpClient http = HttpClientBuilder.create().build();
FileOutputStream fos = new FileOutputStream(file);
CloseableHttpResponse response = http.execute(new HttpGet(url));) {
int sc = response.getStatusLine().getStatusCode();
if (sc == HttpStatus.SC_OK) {
HttpEntity entity = response.getEntity();
entity.writeTo(fos);
} else {
...
}
}
return file;
}
排查代码发现出现在 CompletableFuture.get() 步骤超时
CompletableFuture<List<File>> sequence = sequence(
imgs.stream().map(p -> CompletableFuture.supplyAsync(() -> {
...
}).exceptionally(e -> {
...
})).collect(toList()));
try {
return sequence.get(300L, TimeUnit.SECONDS);
} catch (InterruptedException | ExecutionException | TimeoutException e) {
...
}
考虑到当影像量庞大时候下载速度问题，超时时间设置为5分钟之久。
这么久的超时时间设置，每次方法调用出现都出现TimeoutException问题，猜测是线程堵塞。
项目部署在docker容器，进入bash 。
jps -l // 获取项目进程ID
由于使用了CompletableFuture 异步操作的默认线程池ForkJoinPool
使用jstack 获取项目堆栈日志。
jstack 1(项目进程ID) | grep ForkJoinPool -A 10
获取到的日志部分如下所示。
"ForkJoinPool.commonPool-worker-1" #521 daemon prio=5 os_prio=0 tid=0x00007f4b901be800 nid=0x20e runnable [0x00007f4b5b693000]
java.lang.Thread.State: RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
at java.net.SocketInputStream.read(SocketInputStream.java:171)
at java.net.SocketInputStream.read(SocketInputStream.java:141)
at org.apache.http.impl.io.SessionInputBufferImpl.streamRead(SessionInputBufferImpl.java:137)
at org.apache.http.impl.io.SessionInputBufferImpl.read(SessionInputBufferImpl.java:198)
at org.apache.http.impl.io.ContentLengthInputStream.read(ContentLengthInputStream.java:176)
at org.apache.http.impl.io.ContentLengthInputStream.read(ContentLengthInputStream.java:198)
at org.apache.http.entity.BasicHttpEntity.writeTo(BasicHttpEntity.java:116)
at org.apache.http.impl.execchain.ResponseEntityProxy.writeTo(ResponseEntityProxy.java:101)
at net.ebaolife.tpa.common.util.XXX.download(XXX.java:57)
at net.ebaolife.tpa.common.util.XXX$BatchOp.lambda$null$0(XXX.java:93)
at net.ebaolife.tpa.common.util.XXX$BatchOp$$Lambda$57/1027039641.get(Unknown Source)
at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1590)
at java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1582)
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)
几个ForkJoinPool的线程全部处于RUNNABLE 状态，而且都阻塞在java.net.SocketInputStream#socketRead0 方法上。
查阅资料发现该方法在请求远程服务时候不设置超时时间，由于网络原因很容易阻塞线程，具体原因不做详述。
发现问题后解决即可，设置上socket超时时间：
public File download(String url, String filename) throws IOException {
File file = new File(parent, filename);
RequestConfig requestConfig = RequestConfig.custom()
.setConnectTimeout(TIME_OUT)
.setSocketTimeout(TIME_OUT).build();
HttpGet httpGet = new HttpGet(url);
httpGet.setConfig(requestConfig);
try (CloseableHttpClient http = HttpClientBuilder.create().build();
FileOutputStream fos = new FileOutputStream(file);
CloseableHttpResponse response = http.execute(httpGet)) {
int sc = response.getStatusLine().getStatusCode();
if (sc == HttpStatus.SC_OK) {
HttpEntity entity = response.getEntity();
entity.writeTo(fos);
} else {
...
}
return file;
}
线程池阻塞导致的问题还是很大的，特此记录，使用 CloseableHttpClient 的时候一定注意设置 socket超时时间 以及在使用完后及时关闭各个流，代码中使用到了try resource的方法来优雅关闭流。
一般类只要实现了 Closeable 接口即可使用这类方式。
public abstract class CloseableHttpClient implements HttpClient, Closeable {
...
}
public interface Closeable extends AutoCloseable {
/**
* Closes this stream and releases any system resources associated
* with it. If the stream is already closed then invoking this
* method has no effect.
*
* <p> As noted in {@link AutoCloseable#close()}, cases where the
* close may fail require careful attention. It is strongly advised
* to relinquish the underlying resources and to internally
* <em>mark</em> the {@code Closeable} as closed, prior to throwing
* the {@code IOException}.
*
* @throws IOException if an I/O error occurs
*/
public void close() throws IOException;
}