AQS-ConditionObject 筆記

ConditionObject

屬性	說明
Node firstWaiter	頭節點
Node lastWaiter	尾節點

為Condition接口實作,Condition的目的主要是替代Object的wait,notify,notifyAll方法的,它是基于Lock實作的.(而Lock是來替代synchronized方法).

結構

使用時序圖

關鍵方法

阻塞線程:await

對應Object.wait(),通過AQS機制釋放鎖定的資源,終止目前線程,恢複後使用AQS獨占模式重新鎖定資源

acquireQueued:此時node節點已轉換為AQS中節點

public final void await() throws InterruptedException {
    if (Thread.interrupted())
        throw new InterruptedException();
    Node node = addConditionWaiter();
    long savedState = fullyRelease(node);
    int interruptMode = 0;
    while (!isOnSyncQueue(node)) {
        LockSupport.park(this);
        if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
            break;
    }
    if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
        interruptMode = REINTERRUPT;
    if (node.nextWaiter != null) // clean up if cancelled
        unlinkCancelledWaiters();
    if (interruptMode != 0)
        reportInterruptAfterWait(interruptMode);
}      

喚醒線程:signal

transferForSignal轉換節點後await()中acquireQueued(node,savedState)操作的節點已是AQS中的節點

isHeldExclusively:子類實作.判斷是否獨家持有

public final void signal() {
    if (!isHeldExclusively())
        throw new IllegalMonitorStateException();
    Node first = firstWaiter;
    if (first != null)
        doSignal(first);
}