1、構造方法

• corePoolSize ： 核心執行緒數
• maximumPoolSize ： 最大執行緒數量
• keepAliveTime ： 空閒存活時間
• unit ：時間單位
• workQueue ：阻塞佇列，用來儲存等待執行的任務。
  • ArrayBlockingQueue：陣列有界佇列，先進先出
  • DelayQueue ： 無界阻塞佇列，延遲期滿才能提取元素
  • LinkedBlockingQueue：鏈式結構，先進先出
  • PriorityBlockingQueue：支援優先順序排序的無界佇列，可以自定義實現compareTo()方法指定元素排序。不能保證優先順序元素的順序
  • SynchronousQueue ：容納單元素
  • BlockingDeque ：雙端佇列，在不能夠插入元素的時候，阻塞插入。沒有元素抽取的時候，阻塞抽取。
  • LinkedBlockingDeque：是雙向連結串列實現的雙向併發阻塞佇列。該阻塞佇列同時支援FIFO和FILO兩種操作方式，即可以從佇列的頭和尾同時操作(插入/刪除)；並且，該阻塞佇列是支援執行緒安全。此外，LinkedBlockingDeque還是可選容量的(防止過度膨脹)，即可以指定佇列的容量。如果不指定，預設容量大小等於Integer.MAX_VALUE
• threadFactory：執行緒工廠，用來建立執行緒
• handler ：飽和策略
  • CallerRunsPolicy：用呼叫者所在的執行緒來執行任務
  • AbortPolicy ：預設策略，直接丟擲異常
  • DiscardPolicy ：直接丟棄任務
  • DiscardOldestPolicy：丟棄佇列最前的任務，並執行當前任務

public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue
 
<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.acc = System.getSecurityManager() == null ?
                null :
                AccessController.getContext();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

2、execute方法

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();
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        if (isRunning(c) && workQueue.offer(command)) {
            int recheck = ctl.get();
            if (! isRunning(recheck) && remove(command))
                reject(command);
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
        else if (!addWorker(command, false))
            reject(command);
    }