java - 同步调用锁定条件的 signalAll() 时出现 IllegalMonitorStateException

Question

我有:

static public final ReentrantLock lock  = new ReentrantLock();
static public Condition my_condition    = lock.newCondition();

在 myClass_1 和 myClass_2 类中，我调用:

synchronized (myClass_1.my_condition){
    myClass_1.my_condition.signalAll();
}

这给我 java.lang.IllegalMonitorStateException。我已经通过 signall() 调用进行了同步。可能是什么原因造成的？

Answer 1

这是因为在发送信号之前您没有获得 ReentrantLock 的锁。

阅读以下来自 ReentrantLock#newCondition 的重要声明

If this lock is not held when any of the Condition waiting or signalling methods are called, then an IllegalMonitorStateException is thrown.

此外，请阅读以下来自 Condition 的内容.现在，就像如果线程未获取锁则无法调用 wait() 一样，如果未获取锁则等待或发出信号。

Where a Lock replaces the use of synchronized methods and statements, a Condition replaces the use of the Object monitor methods.

底线:在等待或发出条件信号之前获取锁。

lock.lock();  //Get the lock
while(/* whatever is your condition in myClass_1 and myClass_2 */){  //Or negative condition you want, but some code logic condition...
    my_condition.await();
}
my_condition_2.signal(); //If you want to notify one thread. Like in case of Java's blocking queue, if you want to notify one thread to put or take.
my_condition_2.signalAll(); //If you want to notify all threads.