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This article will explain in detail the internal principle analysis of thread pool in Java, Xiaobian thinks it is quite practical, so share it with you as a reference, I hope you can gain something after reading this article.

Let's first look at the execute method of the ThreadPoolExecutor class:

public void execute(Runnable command) { if (command == null) throw new NullPointerException(); //Get clt, clt records thread pool status and number of running threads. int c = ctl.get(); //When the number of running threads is less than the number of core threads, create threads and put them into the thread pool and run the current task. if (workerCountOf(c)

< corePoolSize) { if (addWorker(command, true)) return; //创建线程失败，重新获取clt。 c = ctl.get(); } //线程池是运行状态并且运行线程大于核心线程数时，把任务放入队列中。 if (isRunning(c) && workQueue.offer(command)) { int recheck = ctl.get(); //重新检查线程池不是运行状态时， //把任务移除队列，并通过拒绝策略对该任务进行处理。 if (! isRunning(recheck) && remove(command)) reject(command); //当前运行线程数为0时，创建线程加入线程池中。 else if (workerCountOf(recheck) == 0) addWorker(null, false); } //运行线程大于核心线程数时并且队列已满时， //创建线程放入线程池中，并且运行当前任务。 else if (!addWorker(command, false)) //运行线程大于最大线程数时，失败则拒绝该任务 reject(command);} 在execute方法中，多次调用的addWorker方法，再看一下这个方法： private boolean addWorker(Runnable firstTask, boolean core) { retry: for (;;) { //获取clt，clt记录着线程池状态和运行线程数。 int c = ctl.get(); //获取线程池的运行状态。 int rs = runStateOf(c); //线程池处于关闭状态，或者当前任务为null //或者队列不为空，则直接返回失败。 if (rs >

= SHUTDOWN && ! (rs == SHUTDOWN && firstTask == null && ! workQueue.isEmpty())) return false; for (;;) { //Get the number of threads in the thread pool int wc = workerCountOf(c); //if the number of threads exceeds CAPACITY, false is returned; //where core is the second argument to the addWorker method, //if true compare based on number of core threads //If false, compare based on maximum number of threads. if (wc >= CAPACITY || wc >= (core ? corePoolSize : maximumPoolSize)) return false; //Try increasing the number of threads, and if successful, jump out of the first for loop if (compareAndIncrementWorkerCount(c)) break retry; //if increasing the number of threads fails, retrieve ctl c = ctl.get(); //If the current operating state is not rs, the state has been changed, //return to the first for loop to continue execution if (runStateOf(c) != rs) continue retry; } } boolean workerStarted = false; boolean workerAdded = false; Worker w = null; try { //Create a Worker object based on the current task w = new Worker(firstTask); final Thread t = w.thread; if (t != null) { final ReentrantLock mainLock = this.mainLock; mainLock.lock(); try { //After acquiring the lock, recheck the thread pool state int rs = runStateOf(ctl.get()); if (rs

< SHUTDOWN || (rs == SHUTDOWN && firstTask == null)) { if (t.isAlive()) throw new IllegalThreadStateException(); //把刚刚创建的线程加入到线程池中 workers.add(w); int s = workers.size(); //记录线程池中出现过的最大线程数量 if (s >

largestPoolSize) largestPoolSize = s; workerAdded = true; } } finally { mainLock.unlock(); } if (workerAdded) { //Start thread and start task t.start(); workerStarted = true; } } } finally { if (! workerStarted) addWorkerFailed(w); } return workerStarted;} About "Java thread pool internal principle analysis" This article is shared here, I hope the above content can be of some help to everyone, so that you can learn more knowledge, if you think the article is good, please share it to let more people see.

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