一文详解tomcat是如何处理HTTP长连接的

public void run() {
    // Loop until destroy() is called
    while (true) {

        boolean hasEvents = false;

        try {
            if (!close) {
                hasEvents = events();
                if (wakeupCounter.getAndSet(-1) > 0) {
                    // If we are here, means we have other stuff to do
                    // Do a non blocking select
                    keyCount = selector.selectNow();
                } else {
                    keyCount = selector.select(selectorTimeout);
                }
                wakeupCounter.set(0);
            }
            if (close) {
                events();
                timeout(0, false);
                try {
                    selector.close();
                } catch (IOException ioe) {
                    log.error(sm.getString("endpoint.nio.selectorCloseFail"), ioe);
                }
                break;
            }
            // Either we timed out or we woke up, process events first
            if (keyCount == 0) {
                hasEvents = (hasEvents | events());
            }
        } catch (Throwable x) {
            ExceptionUtils.handleThrowable(x);
            log.error(sm.getString("endpoint.nio.selectorLoopError"), x);
            continue;
        }

        Iterator<SelectionKey> iterator =
            keyCount > 0 ? selector.selectedKeys().iterator() : null;
        // Walk through the collection of ready keys and dispatch
        // any active event.
        while (iterator != null && iterator.hasNext()) {
            SelectionKey sk = iterator.next();
            iterator.remove();
            NioSocketWrapper socketWrapper = (NioSocketWrapper) sk.attachment();
            // Attachment may be null if another thread has called
            // cancelledKey()
            if (socketWrapper != null) {
                processKey(sk, socketWrapper);
            }
        }

        // Process timeouts
        timeout(keyCount,hasEvents);
    }

    getStopLatch().countDown();
}

protected void timeout(int keyCount, boolean hasEvents) {
    long now = System.currentTimeMillis();
    // nextExpiration初始化是0
    if (nextExpiration > 0 && (keyCount > 0 || hasEvents) && (now < nextExpiration) && !close) {
        return;
    }
    int keycount = 0;
    try {
        // 遍历注册到selector上所有的socket
        for (SelectionKey key : selector.keys()) {
            keycount++;
            NioSocketWrapper socketWrapper = (NioSocketWrapper) key.attachment();
            try {
                if (socketWrapper == null) {
                    // We don't support any keys without attachments
                    if (key.isValid()) {
                        key.cancel();
                    }
                } else if (close) {
                    key.interestOps(0);
                    // Avoid duplicate stop calls
                    socketWrapper.interestOps(0);
                    socketWrapper.close();
                // 如果注册的事件是读写事件
                } else if (socketWrapper.interestOpsHas(SelectionKey.OP_READ) ||
                          socketWrapper.interestOpsHas(SelectionKey.OP_WRITE)) {
                    boolean readTimeout = false;
                    boolean writeTimeout = false;
                    // 检查读超时
                    if (socketWrapper.interestOpsHas(SelectionKey.OP_READ)) {
                        // 用当前时间-上次读时间
                        long delta = now - socketWrapper.getLastRead();
                        long timeout = socketWrapper.getReadTimeout();
                        if (timeout > 0 && delta > timeout) {
                            readTimeout = true;
                        }
                    }
                    // Check for write timeout
                    if (!readTimeout && socketWrapper.interestOpsHas(SelectionKey.OP_WRITE)) {
                        long delta = now - socketWrapper.getLastWrite();
                        long timeout = socketWrapper.getWriteTimeout();
                        if (timeout > 0 && delta > timeout) {
                            writeTimeout = true;
                        }
                    }
                    // 如果已经超时
                    if (readTimeout || writeTimeout) {
                        key.interestOps(0);
                        // Avoid duplicate timeout calls
                        socketWrapper.interestOps(0);
                        socketWrapper.setError(new SocketTimeoutException());
                        if (readTimeout && socketWrapper.readOperation != null) {
                            if (!socketWrapper.readOperation.process()) {
                                socketWrapper.close();
                            }
                        } else if (writeTimeout && socketWrapper.writeOperation != null) {
                            if (!socketWrapper.writeOperation.process()) {
                                socketWrapper.close();
                            }
                        // processSocket中对将socket进行关闭
                        } else if (!processSocket(socketWrapper, SocketEvent.ERROR, true)) {
                            socketWrapper.close();
                        }
                    }
                }
            } catch (CancelledKeyException ckx) {
                if (socketWrapper != null) {
                    socketWrapper.close();
                }
            }
        }
    } catch (ConcurrentModificationException cme) {
        // See https://bz.apache.org/bugzilla/show_bug.cgi?id=57943
        log.warn(sm.getString("endpoint.nio.timeoutCme"), cme);
    }
    // For logging purposes only
    long prevExp = nextExpiration;
    // nextExpiration重新赋值 当前时间+1s，socketProperties.getTimeoutInterval()默认1000
    nextExpiration = System.currentTimeMillis() +
            socketProperties.getTimeoutInterval();
    if (log.isTraceEnabled()) {
        log.trace("timeout completed: keys processed=" + keycount +
                "; now=" + now + "; nextExpiration=" + prevExp +
                "; keyCount=" + keyCount + "; hasEvents=" + hasEvents +
                "; eval=" + ((now < prevExp) && (keyCount>0 || hasEvents) && (!close) ));
    }

}

if (keptAlive) {
    // Haven't read any request data yet so use the keep-alive
    // timeout.
    wrapper.setReadTimeout(keepAliveTimeout);
}

if (to.remaining() >= limit) {
    to.limit(to.position() + limit);
    nRead = fillReadBuffer(block, to);
    if (log.isDebugEnabled()) {
        log.debug("Socket: [" + this + "], Read direct from socket: [" + nRead + "]");
    }
    updateLastRead();
}