线程池之提交优先级与执行优先级

最新推荐文章于 2025-09-10 00:36:58 发布

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最新推荐文章于 2025-09-10 00:36:58 发布 · 2.4k 阅读

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#多线程

本文探讨了在使用Java线程池时遇到的问题，即线程的执行顺序并非按提交顺序进行。分析了线程池的工作原理，提交优先级遵循核心线程、等待队列、非核心线程的顺序，而执行优先级则是核心线程优先，接着是非核心线程，最后是等待队列中的任务。通过分析`execute`方法和`runWorker`方法的逻辑，揭示了线程调度的内部机制。

问题发现

在使用newfixedThreadPool时设置核心线程10，最大线程20，采用arrayBlockingQueue10。
在for循环里打印i,以及线程id，发现线程的顺序是先打印1到10，然后打印21到30。也就是说后提交的数据中间输出。

提交优先级

提交优先级：就是先交付核心线程、等待队列、非核心线程。
在这里插入图片描述
代码如下：

public void execute(Runnable command) {
   
   
    if (command == null)
        throw new NullPointerException();
    /*
     * Proceed in 3 steps:
     *
     * 1. If fewer than corePoolSize threads are running, try to
     * start a new thread with the given command as its first
     * task.  The call to addWorker atomically checks runState and
     * workerCount, and so prevents false alarms that would add
     * threads when it shouldn't, by returning false.
     *
     * 2. If a task can be successfully queued, then we still need
     * to double-check whether we should have added a thread
     * (because existing ones died since last checking) or that
     * the pool shut down since entry into this method. So we
     * recheck state and if necessary roll back the enqueuing if
     * stopped, or start a new thread if there are none.
     *
     * 3. If we cannot queue task, then we try to add a new
     * thread.  If it fails, we know we are shut down or saturated
     * and so reject the task.
     */
    int c = ctl.get();
    // worker数量比核心线程数小，直接创建worker执行任务
    if (workerCountOf(c) < corePoolSize) {
   
   
        if (addWorker(command, true))
            return;
        c = ctl.get