java - 调用 Thread.isInterrupted() 的性能成本是多少？

Question

从 java 源代码来看，它看起来像是放入 native 代码。成本大致相当于 volatile 读取还是需要获取某种类型的锁？

Answer 1

Thread.isInterrupted() 是一个调用成本非常低的函数。还有一些间接调用，但所有调用都足够快。总结:

It must be possible for Java to emulate Thread.currentThread().isInterrupted() by performing the double indirection Thread::current()->_osthread->_interrupted.

Source :

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是这样实现的:

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; }