java - notify()之后的锁获取顺序

Question

假设线程 T1 正在等待进入同步块(synchronized block)，线程 T2 在同步块(synchronized block)内 wait()，并且线程 T3 在同步块(synchronized block)上调用 notify() block 的监视器。

T1有可能在T2继续之前进入区 block 吗？还是T2优先？

Answer 1

Is it possible for T1 to enter the block before T2 proceeds?

是的，这是可能的。 Object.wait(int) 的 javadoc没有指定已通知的线程优先。事实上，它指定应用正常调度规则。

"The thread T is then removed from the wait set for this object and re-enabled for thread scheduling. It then competes in the usual manner with other threads for the right to synchronize on the object ..."

<小时/>

这是您需要编写这样的条件变量代码的原因之一

  private boolean condition = ...
  private Object lock = new Object();  // mutex for 'condition'

  ...

  synchronize (lock) {
      while (!condition) {
           wait(lock);
           // It is UNSAFE to assume that 'condition' is true now.
      }
  }