Nio连接池被hang死

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nio hang 连接池 AbstractNIOConnPool 锁

今天发现Jetty没有响应了，重启就好了，重启之前抓了一个dump分析了下里面的堆栈信息，发现Jetty的所有工作线程都被一把锁给hang住了：

"qtp598461443-127" prio=5 tid=127 WAITING
at sun.misc.Unsafe.park(Native Method)
at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:811)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:842)
Local Variable: java.util.concurrent.locks.AbstractQueuedSynchronizer$Node#286
at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1178)
at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:186)
at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:262)
at org.apache.http.nio.pool.AbstractNIOConnPool.lease(AbstractNIOConnPool.java:271)
Local Variable: org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager$InternalPoolEntryCallback#35
Local Variable: org.apache.http.concurrent.BasicFuture#187
at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.requestConnection(PoolingNHttpClientConnectionManager.java:265)
Local Variable: org.apache.http.concurrent.BasicFuture#98
Local Variable: org.apache.http.impl.nio.client.AbstractClientExchangeHandler$1#34
Local Variable: org.apache.http.nio.conn.NoopIOSessionStrategy#1
at org.apache.http.impl.nio.client.AbstractClientExchangeHandler.requestConnection(AbstractClientExchangeHandler.java:358)
Local Variable: org.apache.http.client.config.RequestConfig#96
Local Variable: org.apache.http.conn.routing.HttpRoute#215
at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl.start(DefaultClientExchangeHandlerImpl.java:125)
at org.apache.http.impl.nio.client.InternalHttpAsyncClient.execute(InternalHttpAsyncClient.java:141)
Local Variable: org.apache.http.nio.client.methods.HttpAsyncMethods$RequestProducerImpl#51
Local Variable: org.apache.http.concurrent.BasicFuture#99
Local Variable: org.apache.http.nio.protocol.BasicAsyncResponseConsumer#40
Local Variable: org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl#42
at org.apache.http.impl.nio.client.CloseableHttpAsyncClient.execute(CloseableHttpAsyncClient.java:74)
at org.apache.http.impl.nio.client.CloseableHttpAsyncClient.execute(CloseableHttpAsyncClient.java:107)
Local Variable: org.apache.http.HttpHost#127
Local Variable: org.apache.http.client.protocol.HttpClientContext#49
******
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1322)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:473)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:479)
Local Variable: org.eclipse.jetty.security.ConstraintSecurityHandler#1
Local Variable: org.eclipse.jetty.security.authentication.BasicAuthenticator#1
Local Variable: org.eclipse.jetty.security.authentication.DeferredAuthentication#1
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:226)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:929)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:403)
Local Variable: org.eclipse.jetty.server.DispatcherType#1
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:184)
Local Variable: org.eclipse.jetty.server.session.SessionHandler#1
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:864)
Local Variable: java.lang.String#241755
Local Variable: sun.misc.Launcher$AppClassLoader#1
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)
at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:247)
Local Variable: org.eclipse.jetty.util.SingletonList#3
Local Variable: org.eclipse.jetty.server.handler.ContextHandlerCollection#1
Local Variable: org.eclipse.jetty.webapp.WebAppContext#1
at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:151)
Local Variable: org.eclipse.jetty.server.Response#610
Local Variable: org.eclipse.jetty.server.Request#498
Local Variable: org.eclipse.jetty.server.handler.HandlerCollection#1
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:114)
at org.eclipse.jetty.server.Server.handle(Server.java:352)
at org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:596)
Local Variable: org.eclipse.jetty.server.Server#1
Local Variable: java.lang.String#204075
at org.eclipse.jetty.server.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:1051)
Local Variable: org.eclipse.jetty.server.HttpConnection$RequestHandler#416
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:590)
at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:212)
Local Variable: org.eclipse.jetty.http.HttpParser#411
at org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:426)
Local Variable: org.eclipse.jetty.server.nio.SelectChannelConnector$3#616
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:508)
Local Variable: org.eclipse.jetty.io.nio.SelectChannelEndPoint#585
at org.eclipse.jetty.io.nio.SelectChannelEndPoint.access$000(SelectChannelEndPoint.java:34)
at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:40)
at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:451)
Local Variable: org.eclipse.jetty.io.nio.SelectChannelEndPoint$1#414
at java.lang.Thread.run(Thread.java:662)

我把关键的堆栈信息标红了，Jetty的工作线程在向异步连接池PoolingNHttpClientConnectionManager申请链接的时候，拿不到锁，线程就hang在那儿了。

看了下Apache的Nio连接池的代码发现里面有一把很重要的锁：

/**
 * Abstract non-blocking connection pool.
 *
 * @param <T> route
 * @param <C> connection object
 * @param <E> pool entry
 *
 * @since 4.2
 */
@ThreadSafe
public abstract class AbstractNIOConnPool<T, C, E extends PoolEntry<T, C>>
                                                  implements ConnPool<T, E>, ConnPoolControl<T> {

    private final ConnectingIOReactor ioreactor;
    private final NIOConnFactory<T, C> connFactory;
    private final SocketAddressResolver<T> addressResolver;
    private final SessionRequestCallback sessionRequestCallback;
    private final Map<T, RouteSpecificPool<T, C, E>> routeToPool;
    private final LinkedList<LeaseRequest<T, C, E>> leasingRequests;
    private final Set<SessionRequest> pending;
    private final Set<E> leased;
    private final LinkedList<E> available;
    private final ConcurrentLinkedQueue<LeaseRequest<T, C, E>> completedRequests;
    private final Map<T, Integer> maxPerRoute;
    private final Lock lock;
    private final AtomicBoolean isShutDown;

    private volatile int defaultMaxPerRoute;
    private volatile int maxTotal;
.

这把锁无敌了，所有对连接池链接的状态修改，都需要获取这把锁，比如获取链接：

/**
 * @since 4.3
 */
public Future<E> lease(
        final T route, final Object state,
        final long connectTimeout, final long leaseTimeout, final TimeUnit tunit,
        final FutureCallback<E> callback) {
    Args.notNull(route, "Route");
Args.notNull(tunit, "Time unit");
Asserts.check(!this.isShutDown.get(), "Connection pool shut down");
    final BasicFuture<E> future = new BasicFuture<E>(callback);
    this.lock.lock();
    try {
        final long timeout = connectTimeout > 0 ? tunit.toMillis(connectTimeout) : 0;
        final LeaseRequest<T, C, E> request = new LeaseRequest<T, C, E>(route, state, timeout, leaseTimeout, future);
        final boolean completed = processPendingRequest(request);
        if (!request.isDone() && !completed) {
            this.leasingRequests.add(request);
}
        if (request.isDone()) {
            this.completedRequests.add(request);
}
    } finally {
        this.lock.unlock();
}
    fireCallbacks();
    return future;

或者活干完了，把连接还回来：

protected void requestCompleted(final SessionRequest request) {
    if (this.isShutDown.get()) {
        return;
}
    @SuppressWarnings("unchecked")
    final
T route = (T) request.getAttachment();
    this.lock.lock();
    try {
        this.pending.remove(request);
        final RouteSpecificPool<T, C, E> pool = getPool(route);
        final IOSession session = request.getSession();
        try {
            final C conn = this.connFactory.create(route, session);
            final E entry = pool.createEntry(request, conn);
            this.leased.add(entry);
pool.completed(request, entry);
onLease(entry);
} catch (final IOException ex) {
            pool.failed(request, ex);
}
    } finally {
        this.lock.unlock();
}
    fireCallbacks();
}

这样如果有一个线程在使用连接资源过程中，在释放锁之前hang住了，整个连接池就费了，想取连接的工作线程会hang在这把锁上，想归还连接的工作线程也会hang在这把锁上，然后所有线程都hang住之后，整个服务就不能工作了。

然后我看了整个线程堆栈信息，还真有一个拿着锁的线程在释放连接的时候被hang住了：

"I/O dispatcher 48" prio=5 tid=83 RUNNABLE at sun.nio.ch.FileDispatcher.preClose0(Native Method) at sun.nio.ch.SocketDispatcher.preClose(SocketDispatcher.java:41) Local Variable: java.io.FileDescriptor#261 Local Variable: sun.nio.ch.SocketDispatcher#1 at sun.nio.ch.SocketChannelImpl.implCloseSelectableChannel(SocketChannelImpl.java:677) Local Variable: java.lang.Object#2674 at java.nio.channels.spi.AbstractSelectableChannel.implCloseChannel(AbstractSelectableChannel.java:201) at java.nio.channels.spi.AbstractInterruptibleChannel.close(AbstractInterruptibleChannel.java:97) Local Variable: java.lang.Object#2669 Local Variable: sun.nio.ch.SocketChannelImpl#342 at org.apache.http.impl.nio.reactor.IOSessionImpl.close(IOSessionImpl.java:226) at org.apache.http.impl.nio.NHttpConnectionBase.close(NHttpConnectionBase.java:513) at org.apache.http.impl.nio.conn.CPoolEntry.closeConnection(CPoolEntry.java:74) at org.apache.http.impl.nio.conn.CPoolEntry.close(CPoolEntry.java:100) at org.apache.http.nio.pool.AbstractNIOConnPool.processPendingRequest(AbstractNIOConnPool.java:375) Local Variable: org.apache.http.conn.routing.HttpRoute#189 at org.apache.http.nio.pool.AbstractNIOConnPool.processNextPendingRequest(AbstractNIOConnPool.java:343) Local Variable: java.util.LinkedList$ListItr#1 Local Variable: org.apache.http.nio.pool.LeaseRequest#1 at org.apache.http.nio.pool.AbstractNIOConnPool.release(AbstractNIOConnPool.java:317) Local Variable: org.apache.http.nio.pool.AbstractNIOConnPool$2#25 at org.apache.http.impl.nio.conn.PoolingNHttpClientConnectionManager.releaseConnection(PoolingNHttpClientConnectionManager.java:302) Local Variable: org.apache.http.impl.nio.conn.CPoolEntry#49 at org.apache.http.impl.nio.client.AbstractClientExchangeHandler.releaseConnection(AbstractClientExchangeHandler.java:238) Local Variable: org.apache.http.impl.nio.conn.CPoolProxy#12 at org.apache.http.impl.nio.client.MainClientExec.responseCompleted(MainClientExec.java:387) Local Variable: org.apache.http.nio.protocol.BasicAsyncResponseConsumer#37 Local Variable: org.apache.http.impl.nio.client.InternalState#95 Local Variable: org.apache.http.client.protocol.HttpClientContext#16 Local Variable: org.apache.http.message.BasicHttpResponse#3 at org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl.responseCompleted(DefaultClientExchangeHandlerImpl.java:168) at org.apache.http.nio.protocol.HttpAsyncRequestExecutor.processResponse(HttpAsyncRequestExecutor.java:412) Local Variable: org.apache.http.nio.protocol.HttpAsyncRequestExecutor$State#8 Local Variable: org.apache.http.impl.nio.client.DefaultClientExchangeHandlerImpl#40 at org.apache.http.nio.protocol.HttpAsyncRequestExecutor.inputReady(HttpAsyncRequestExecutor.java:305) at org.apache.http.impl.nio.DefaultNHttpClientConnection.consumeInput(DefaultNHttpClientConnection.java:267) Local Variable: org.apache.http.impl.nio.conn.ManagedNHttpClientConnectionImpl#42 at org.apache.http.impl.nio.client.InternalIODispatch.onInputReady(InternalIODispatch.java:81) at org.apache.http.impl.nio.client.InternalIODispatch.onInputReady(InternalIODispatch.java:39) at org.apache.http.impl.nio.reactor.AbstractIODispatch.inputReady(AbstractIODispatch.java:116) at org.apache.http.impl.nio.reactor.BaseIOReactor.readable(BaseIOReactor.java:164) at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvent(AbstractIOReactor.java:339) Local Variable: sun.nio.ch.SelectionKeyImpl#94 Local Variable: org.apache.http.impl.nio.reactor.IOSessionImpl#6 at org.apache.http.impl.nio.reactor.AbstractIOReactor.processEvents(AbstractIOReactor.java:317) Local Variable: java.util.HashMap$KeyIterator#18 Local Variable: sun.nio.ch.Util$H2#3 at org.apache.http.impl.nio.reactor.AbstractIOReactor.execute(AbstractIOReactor.java:278) at org.apache.http.impl.nio.reactor.BaseIOReactor.execute(BaseIOReactor.java:106) Local Variable: org.apache.http.impl.nio.reactor.BaseIOReactor#2 at org.apache.http.impl.nio.reactor.AbstractMultiworkerIOReactor$Worker.run(AbstractMultiworkerIOReactor.java:590) Local Variable: org.apache.http.impl.nio.reactor.AbstractMultiworkerIOReactor$Worker#2 at java.lang.Thread.run(Thread.java:662)

一个线程hang住了，把所有线程都hang住了，并且没有保护机制，apache的这个线程池是否需要改进一下？

至于线程为什么在关闭连接的时候被hang住了，查了很多资料，国内外的开发者一直表示可能是在设置TCP连接的SO_LINGER这个属性不当导致的一个bug。SO_LINGER选项用来设置延迟关闭的时间，等待SOCKET发送缓冲区中的数据发送完成。没有设置该选项时，在调用close()后，在发送完FIN后会立即进行一些清理工作并返回。如果设置了SO_LINGER选项，并且等待时间为正值，则在清理之前会等待一段时间。我的程序这个属性设置为100,可能在处理这个等待的过程中遇到一个系统bug或者别的原因，就hang住了。这个属性如果不设置反而不会出现hang的问题。

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