调用Thread.isInterrupted()的性能成本是多少？

Question

从java源代码看,它看起来像是本机代码.成本大致相当于易失性读取还是需要获取某种类型的锁定？

Answer 1

Thread.isInterrupted()是一个非常便宜的电话功能.有一些更多的间接,但所有电话都足够快.总结一下:

Java必须可以Thread.currentThread().isInterrupted()通过执行双重间接来模拟Thread::current()->_osthread->_interrupted.

来源:

bool os::is_interrupted(Thread* thread, bool clear_interrupted) {
  assert(Thread::current() == thread || Threads_lock->owned_by_self(),
    "possibility of dangling Thread pointer");

  OSThread* osthread = thread->osthread();

  bool interrupted = osthread->interrupted();

  if (interrupted && clear_interrupted) {
    osthread->set_interrupted(false);
    // consider thread->_SleepEvent->reset() ... optional optimization
  }

  return interrupted;
}

OSThread 像这样实现:

volatile jint _interrupted;     // Thread.isInterrupted state

// Note:  _interrupted must be jint, so that Java intrinsics can access it.
// The value stored there must be either 0 or 1.  It must be possible
// for Java to emulate Thread.currentThread().isInterrupted() by performing
// the double indirection Thread::current()->_osthread->_interrupted.
....
volatile bool interrupted() const                 { return _interrupted != 0; }