线程-FutureTask总结

2019-09-08 | 阅读：次

futuretask只会执行一次,可用于创建缓存等

run方法

if (state != NEW ||
            !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                         null, Thread.currentThread()))
            return;

get()方法会一直阻塞，当使用线程池 DiscardPolicy和DiscardOldestPolicy的时候需要注意，否则会一直阻塞

FutureTask内部有一个state用来展示任务的状态,并且是volatile修饰的

     * Possible state transitions:
     * NEW -> COMPLETING -> NORMAL
     * NEW -> COMPLETING -> EXCEPTIONAL
     * NEW -> CANCELLED
     * NEW -> INTERRUPTING -> INTERRUPTED
     */
    private volatile int state;
    private static final int NEW          = 0;
    private static final int COMPLETING   = 1;
    private static final int NORMAL       = 2;
    private static final int EXCEPTIONAL  = 3;
    private static final int CANCELLED    = 4;
    private static final int INTERRUPTING = 5;
    private static final int INTERRUPTED  = 6;