What is the performance cost of calling Thread.isInterrupted()?

Question

From the java sources, it look like to drops into native code. Is the cost roughly equivalent to a volatile read or does it need to acquire a lock of some type?

Answer 1

Thread.isInterrupted() is a very cheap function to call. There a few more indirections but all calls are quick enough. To summarize:

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 is implemented like this:

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; }