在我们的异步 servlet 中修复同步问题后，我们仍然很少见
java.io.IOException: Closed while Pending/Unready
来自码头的警告。通过上面的修复，在我们的生产系统中，它从每天约 90 次减少到每天约 5 次。这种情况很少见，而且看起来好多了，但可能仍然缺少一些小东西。
完整的堆栈跟踪：
[jetty-63523] (HttpOutput.java:287) -
java.io.IOException: Closed while Pending/Unready
at org.eclipse.jetty.server.HttpOutput.close(HttpOutput.java:285)
at org.eclipse.jetty.server.Response.closeOutput(Response.java:1044)
at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:493)
at org.eclipse.jetty.server.HttpChannel.run(HttpChannel.java:293)
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:762)
at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:680)
at java.lang.Thread.run(Thread.java:748)
写入输出流（不同步）的唯一代码如下setContentType()，setStatus()并flushBuffer()在此处调用：
@Override
protected void doPost(final HttpServletRequest req, final HttpServletResponse resp)
throws ServletException, IOException {
resp.setContentType(MediaType.OCTET_STREAM.type());
resp.setStatus(HttpServletResponse.SC_OK);
resp.setBufferSize(4096);
resp.flushBuffer();
final AsyncContext async = req.startAsync();
async.setTimeout(5_000); // millis
final ServletOutputStream output = resp.getOutputStream();
final QueueWriteListener writeListener = new QueueWriteListener(async, output);
async.addListener(writeListener);
output.setWriteListener(writeListener);
}
这在我们QueueWriteListener的设置之前运行，所以如果flushBuffer()是同步的，它应该不是问题。
无论如何，查找 Jetty 的源代码，Reponse.flush()调用HttpOutput.flush()其中调用new AsyncFlush().iterate()似乎可疑但调试doPost()/flushBuffer()这个case分支没有运行。
完整代码：
@Override
protected void doPost(final HttpServletRequest req, final HttpServletResponse resp)
throws ServletException, IOException {
resp.setContentType(MediaType.OCTET_STREAM.type());
resp.setStatus(HttpServletResponse.SC_OK);
resp.setBufferSize(4096);
resp.flushBuffer();
final AsyncContext async = req.startAsync();
async.setTimeout(5_000); // millis
final ServletOutputStream output = resp.getOutputStream();
final QueueWriteListener writeListener = new QueueWriteListener(async, output);
async.addListener(writeListener);
output.setWriteListener(writeListener);
}
private static class QueueWriteListener implements AsyncListener, WriteListener {
private static final Logger logger = LoggerFactory.getLogger(QueueWriteListener.class);
private final AsyncContext asyncContext;
private final ServletOutputStream output;
@GuardedBy("this")
private boolean completed = false;
public QueueWriteListener(final AsyncContext asyncContext, final ServletOutputStream output) {
this.asyncContext = checkNotNull(asyncContext, "asyncContext cannot be null");
this.output = checkNotNull(output, "output cannot be null");
}
@Override
public void onWritePossible() throws IOException {
writeImpl();
}
private synchronized void writeImpl() throws IOException {
if (completed) {
return;
}
while (output.isReady()) {
final byte[] message = getNextMessage();
if (message == null) {
output.flush();
return;
}
output.write(message);
}
}
private synchronized void completeImpl() {
// also stops DataFeederThread to call bufferArrived
completed = true;
asyncContext.complete();
}
@Override
public void onError(final Throwable t) {
logger.error("Writer.onError", t);
completeImpl();
}
public void dataArrived() {
try {
writeImpl();
} catch (RuntimeException | IOException e) {
...
}
}
public void noMoreData() {
completeImpl();
}
@Override
public synchronized void onComplete(final AsyncEvent event) throws IOException {
completed = true; // might not needed but does not hurt
}
@Override
public synchronized void onTimeout(final AsyncEvent event) throws IOException {
completeImpl();
}
@Override
public void onError(final AsyncEvent event) throws IOException {
logger.error("onError", event.getThrowable());
}
...
}
因此，似乎在 Jetty 完成和（异步）关闭输出之间，没有人可以写入输出，因此其状态不应更改为挂起或未就绪。尽管如此，它仍然以某种方式发生。Closed while Pending/Unready此警告的原因可能是什么？
我检查了我们的日志（没有相关的）。
onError(AsyncEvent event)（还）不在synchronized我们的代码中，但它不相关，因为它的日志消息从未出现在我们的日志中。
GitHub相关讨论：https ://github.com/eclipse/jetty.project/issues/2689