关于线程池:线程池

34次阅读

共计 1758 个字符，预计需要花费 5 分钟才能阅读完成。

下面是提交了工作后，线程池解决流程。如果想在工作提交前预热线程池能够应用 prestartAllCoreThreads 提前创立线程。
须要留神的是，上图中两个中央的创立线程都是须要加锁的，相干代码如下图：

private boolean addWorker(Runnable firstTask, boolean core) {
        retry:
        for (;;) {int c = ctl.get();
            int rs = runStateOf(c);

            // Check if queue empty only if necessary.
            if (rs >= SHUTDOWN &&
                ! (rs == SHUTDOWN &&
                   firstTask == null &&
                   ! workQueue.isEmpty()))
                return false;

            for (;;) {int wc = workerCountOf(c);
                if (wc >= CAPACITY ||
                    wc >= (core ? corePoolSize : maximumPoolSize))
                    return false;
                if (compareAndIncrementWorkerCount(c))
                    break retry;
                c = ctl.get();  // Re-read ctl
                if (runStateOf(c) != rs)
                    continue retry;
                // else CAS failed due to workerCount change; retry inner loop
            }
        }

        boolean workerStarted = false;
        boolean workerAdded = false;
        Worker w = null;
        try {
            // 这里的外部类 Worker 继承了 AbstractQueuedSynchronizer，也实现了 Runnable
            //Worker 外面有个 Thread 属性，每次创立工作的时候都会对应创立一个线程
            w = new Worker(firstTask);
            final Thread t = w.thread;
            if (t != null) {
                final ReentrantLock mainLock = this.mainLock;
                // 加锁
                mainLock.lock();
                try {
                    // Recheck while holding lock.
                    // Back out on ThreadFactory failure or if
                    // shut down before lock acquired.
                    int rs = runStateOf(ctl.get());

                    if (rs < SHUTDOWN ||
                        (rs == SHUTDOWN && firstTask == null)) {if (t.isAlive()) // precheck that t is startable
                            throw new IllegalThreadStateException();
                        workers.add(w);
                        int s = workers.size();
                        if (s > largestPoolSize)
                            largestPoolSize = s;
                        workerAdded = true;
                    }
                } finally {mainLock.unlock();
                }
                if (workerAdded) {t.start();
                    workerStarted = true;
                }
            }
        } finally {if (! workerStarted)
                addWorkerFailed(w);
        }
        return workerStarted;
    }

这里再列一下几种工作队列：

ArrayBlockingQueue: 基于数组构造的有界阻塞队列，队列按 FIFO 准则对元素进行排序。
LinkedBlockingQueue: 基于链表构造的阻塞队列，同样按 FIFO 准则排序，吞吐量通常高于 ArrayBlockingQueue。
SynchronousQueue: 自身不存储元素的阻塞队列，每次插入须等到另一个线程调用移除操作，否则插入操作会始终阻塞，吞吐量要高于 LinkedBlockingQueue。
PriorityBlockingQueue: 具备优先级的有限阻塞队列。

几种饱和策略：