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我在使用 Java 6 的 ThreadPoolExecutor 时遇到了一个奇怪的问题。有时当我动态更改 corePoolSize 时,我观察到线程池没有处理应有的任务。

例如,如果我有 4 个作为 corePoolSize 并且有很多任务在队列中等待,则执行程序最多处理 3 个,有时甚至是 2 个。

在调查问题时,我注意到当我增加或减少 corePoolSize 时,我从未更改过 maxPoolSize。从我的申请开始,它一直是 1。

从未在 Java 文档中找到提及 maxPoolSize 小于核心的影响的声明。

然后,当我检查源代码时,我注意到在 costructor 和 setCorePoolSize 方法中,都会检查 maxPoolSize 小于 corePoolSize 的位置,如果抛出了非法ArgumentException。查看下面的代码。

构造函数

public ThreadPoolExecutor(
    int corePoolSize,
    int maximumPoolSize,
    long keepAliveTime,
    TimeUnit unit,
    BlockingQueue<Runnable> workQueue,
    ThreadFactory threadFactory,
    RejectedExecutionHandler handler
) {
    if (corePoolSize < 0 ||
        maximumPoolSize <= 0 ||
        maximumPoolSize < corePoolSize ||
        keepAliveTime < 0)
            throw new IllegalArgumentException();
    if (workQueue == null || threadFactory == null || handler == null)
        throw new NullPointerException();
    this.corePoolSize = corePoolSize;
    this.maximumPoolSize = maximumPoolSize;
    this.workQueue = workQueue;
    this.keepAliveTime = unit.toNanos(keepAliveTime);
    this.threadFactory = threadFactory;
    this.handler = handler;
}

设置最大池大小

public void setMaximumPoolSize(int maximumPoolSize) {
    if (maximumPoolSize <= 0 || maximumPoolSize < corePoolSize)
        throw new IllegalArgumentException();
    final ReentrantLock mainLock = this.mainLock;
    mainLock.lock();
    try {
        int extra = this.maximumPoolSize - maximumPoolSize;
        this.maximumPoolSize = maximumPoolSize;
        if (extra > 0 && poolSize > maximumPoolSize) {
            try {
                Iterator<Worker> it = workers.iterator();
                while (it.hasNext() &&
                       extra > 0 &&
                       poolSize > maximumPoolSize) {
                    it.next().interruptIfIdle();
                    --extra;
                }
            } catch (SecurityException ignore) {
                // Not an error; it is OK if the threads stay live
            }
        }
    } finally {
        mainLock.unlock();
    }
}

所以,显然这是一个不受欢迎的情况。但是在 setCorePoolSize 中没有检查,导致 maximumPoolSize 最终小于 corePoolSize,并且没有记录这种情况的影响。

设置核心池大小

public void setCorePoolSize(int corePoolSize) {
    if (corePoolSize < 0)
        throw new IllegalArgumentException();
    final ReentrantLock mainLock = this.mainLock;
    mainLock.lock();
    try {
        int extra = this.corePoolSize - corePoolSize;
        this.corePoolSize = corePoolSize;
        if (extra < 0) {
            int n = workQueue.size(); // don't add more threads than tasks
            while (extra++ < 0 && n-- > 0 && poolSize < corePoolSize) {
                Thread t = addThread(null);
                if (t == null)
                    break;
            }
        }
        else if (extra > 0 && poolSize > corePoolSize) {
            try {
                Iterator<Worker> it = workers.iterator();
                while (it.hasNext() &&
                       extra-- > 0 &&
                       poolSize > corePoolSize &&
                       workQueue.remainingCapacity() == 0)
                    it.next().interruptIfIdle();
            } catch (SecurityException ignore) {
                // Not an error; it is OK if the threads stay live
            }
        }
    } finally {
        mainLock.unlock();
    }
}

你不认为应该有一种机制来防止这种情况结束吗?

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1 回答 1

0

我认为,你是对的,应该有一个像这样的测试

if (corePoolSize < 0 || corePoolSize > maxPoolSize)
    throw new IllegalArgumentException();

但是您可以在调用之前轻松地对此进行测试,setCorePoolSize并在必要时调整最大池大小。即使有这样的测试,您也必须在调用之前检查最大池大小setCorePoolSize以避免获得IllegalArgumentException...

于 2013-09-26T16:16:07.780 回答