java - 在许 cocoa 用之前，Semaphore.tryAcquire(...) 会阻塞还是自旋？

Question

如果不公平的信号量许可不是立即可用的，tryAcquire(long timeout, TimeUnit unit) 会阻塞直到许 cocoa 用(即让出执行)，还是旋转直到许 cocoa 用？

如果调用旋转并且系统有一堆信号量，系统是否会面临有大量旋转信号量的风险？

Answer 1

根据 javadoc:

If no permit is available then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of three things happens:

• Some other thread invokes the release() method for this semaphore and the current thread is next to be assigned a permit; or
• Some other thread interrupts the current thread; or
• The specified waiting time elapses

这表明线程被标记为阻塞(作为灰色状态放入阻塞队列)，这允许处理器执行其他工作。