了解 ThreadPoolExecutor 中的 poolSize

Question

我看了ThreadPoolExecutor类的execute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
    }
}

但如果满足poolSize >= corePoolSize 条件，似乎什么都没有发生！

因为如果ORcondition 的第一部分为真，则不会执行第二部分：

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

根据the rules for thread creation，这里也是maximumPoolSize。如果线程数等于（或大于）corePoolSize 且小于maxPoolSize，则应为任务创建新线程或将任务添加到队列中。

那么为什么如果poolSize 大于或等于corePoolSize 什么都不应该发生呢？..

Answer 1

addIfUnderCorePoolSize 将为这个执行器创建一个新的“核心”线程。 如果执行器中的线程数（poolSize）已经大于或等于“核心”线程数（corePoolSize），那么显然不需要创建更多的“核心”线程。

也许扩展OR条件会更清楚一点：

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
    }
}