超过 ConcurrentWebSocketSessionDecorator bufferSizeLimit 时如何刷新缓冲区？

Question

我在项目中使用Spring Websocket，发现ConcurrentWebSocketSessionDecorator在超出bufferSizeLimit时停止了，但是没有办法恢复。

我是这样用的：

try {
    if (concurrentWebSocketSessionDecorator.isOpen()) {
        concurrentWebSocketSessionDecorator.sendMessage(message);
    }
} catch (SessionLimitExceededException se) {
    logger.warn("sendMessage exceed limit: ", se);
    // TODO flush buffer
} catch (IOException ie) {
    logger.error("sendMessage failed: ", ie);
}

我看了concurrentWebSocketSessionDecorator的代码，方法checkSessionLimits设置limitExceeded=true并抛出SessionLimitExceededException超出缓冲区大小，但我找不到任何设置 limitExceeded=false 的方法。如何刷新缓冲区并重置 limitExceeded？

public void sendMessage(WebSocketMessage<?> message) throws IOException {
    if (shouldNotSend()) {
        return;
    }

    this.buffer.add(message);
    this.bufferSize.addAndGet(message.getPayloadLength());

    do {
        if (!tryFlushMessageBuffer()) {
            if (logger.isTraceEnabled()) {
                String text = String.format("Another send already in progress: " +
                        "session id '%s':, \"in-progress\" send time %d (ms), buffer size %d bytes",
                        getId(), getTimeSinceSendStarted(), getBufferSize());
                logger.trace(text);
            }
            checkSessionLimits();
            break;
        }
    }
    while (!this.buffer.isEmpty() && !shouldNotSend());
}

Answer 1

它在已经运行的tryFlushMessageBuffer()中自行刷新：

private boolean tryFlushMessageBuffer() throws IOException {
    if (this.flushLock.tryLock()) {
        try {
            while (true) {
                WebSocketMessage<?> message = this.buffer.poll();
                if (message == null || shouldNotSend()) {
                    break;
                }
                this.bufferSize.addAndGet(message.getPayloadLength() * -1);
                this.sendStartTime = System.currentTimeMillis();
                getDelegate().sendMessage(message);
                this.sendStartTime = 0;
            }
        }
        finally {
            this.sendStartTime = 0;
            this.flushLock.unlock();
        }
        return true;
    }
    return false;
}

我明白你关于limitExceeded 标志的观点：我们只是不去那个tryFlushMessageBuffer()，因为我们已经在shouldNotSend() 之后存在。那是因为你是对的，limitExceeded 永远不会被重置。

听起来真的像一个错误。请就此事提出 JIRA：https://jira.spring.io/projects/SPR