final boolean tryUnpush(ForkJoinTask<?> t) {
    ForkJoinTask<?>[] a; int s;
    if ((a = array) != null && (s = top) != base &&
        U.compareAndSwapObject
        (a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
        U.putOrderedInt(this, QTOP, s);
        return true;
    }
    return false;
}

public final V join() {
    int s;
    if ((s = doJoin() & DONE_MASK) != NORMAL)
        // 如果没有正常完成去处理异常
        reportException(s);
    return getRawResult();
}

private int doJoin() {
    int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
    // status<0表示任务已经执行完毕
    return (s = status) < 0 ? s :
    ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
        (w = (wt = (ForkJoinWorkerThread)t).workQueue).
        tryUnpush(this) && (s = doExec()) < 0 ? s :
    wt.pool.awaitJoin(w, this, 0L) :
    externalAwaitDone();
}

public void add(long x) {
    Cell[] as; long b, v; int m; Cell a;
    // cells非null或者在base上cas递增失败
    if ((as = cells) != null || !casBase(b = base, b + x)) {
        boolean uncontended = true;
        if (as == null || (m = as.length - 1) < 0 ||
            // getProbe()是个随机数，与m求与运算，能获得一个最小0最大m的数
            (a = as[getProbe() & m]) == null ||
            // 利用随机数，去cells上随机取一个Cell做CAS递增
            !(uncontended = a.cas(v = a.value, v + x)))
            // 如果递增失败，即出现竞争，调longAccumulate方法
            longAccumulate(x, null, uncontended);
    }
}

/**
 * The main pool control state, ctl, is an atomic integer packing
 * two conceptual fields
 *   workerCount, indicating the effective number of threads
 *   runState,    indicating whether running, shutting down etc
 */
 private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));