Question

我瞥了execute班的ThreadPoolExecutor方法。这似乎非常简短：

public void execute(Runnable command) {
    if (command == null)
        throw new NullPointerException();
    if (poolSize >= corePoolSize || !addIfUnderCorePoolSize(command)) {
        if (runState == RUNNING && workQueue.offer(command)) {
            if (runState != RUNNING || poolSize == 0)
                ensureQueuedTaskHandled(command);
        }
        else if (!addIfUnderMaximumPoolSize(command))
            reject(command); // is shutdown or saturated
    }
}

但如果条件poolSize >= corePoolSize满足，似乎没有任何事情发生！

由于OR条件的第一部分是真的，第二部分不会被执行：

if (true || anyMethodWillNotBeExecuted()) { ... }

根据the rules for thread creation，此处也是maximumPoolSize。如果线程数等于（或大于）corePoolSize且小于maxPoolSize，则应为任务或任务创建新线程，应添加到队列中。

那么为什么在poolSize大于或等于corePoolSize的情况下会发生什么呢？

Answer 1

addIfUnderCorePoolSize将创建一个新的＆＃34;核心＆＃34;这个执行者的线程。如果执行程序中的线程数（poolSize）已经大于或等于＆＃34;核心数＆＃34;线程（corePoolSize），显然没有必要创建更多＆＃34;核心＆＃34;线程。

也许扩展OR条件会更清楚：

public void execute(Runnable command) {
    if (command == null)
        throw new NullPointerException();
    if (poolSize >= corePoolSize) {
        // there are enough core threads
        // let's try to put task on the queue
        if (runState == RUNNING && workQueue.offer(command)) {
            if (runState != RUNNING || poolSize == 0)
                ensureQueuedTaskHandled(command);
        } else if (!addIfUnderMaximumPoolSize(command))
            reject(command); // is shutdown or saturated
    } else if (addIfUnderCorePoolSize(command)) {
        // there was not enough core threads, so we started one
        // the task is being executed on a new thread, so there's nothing else to be done here
        return;
    } else {
        // there are enough core threads
        // but we could not start a new thread
        // so let's try to add it to the queue
        if (runState == RUNNING && workQueue.offer(command)) {
            if (runState != RUNNING || poolSize == 0)
                ensureQueuedTaskHandled(command);
        } else if (!addIfUnderMaximumPoolSize(command))
            reject(command); // is shutdown or saturated
    }
}

了解ThreadPoolExecutor中的poolSize

1 个答案: