the notifyAll ()
method is called when the Thread is finished, but not in the Java
source code, but in the native code of jdk
.
openjdk 7
in the source code:
/ jdk7/hotspot/src/os/linux/vm/os_linux.cpp
int ret = pthread_create(&tid, &attr, (void* (*)(void*)) java_start, thread);
static void *java_start(Thread *thread) {
...
thread->run();
return 0;
}
thread
in the
parameter is actually an instance of JavaThread
, while in the internal implementation of JavaThread
, lock.notify_all (thread)
is called before the end of the run
method execution to notify all join
waiting threads. The source code is as follows:
/ jdk7/hotspot/src/share/vm/runtime/thread.cpp
void JavaThread::run() {
...
thread_main_inner();
}
void JavaThread::thread_main_inner() {
...
this->exit(false);
delete this;
}
void JavaThread::exit(bool destroy_vm, ExitType exit_type) {
...
// Notify waiters on thread object. This has to be done after exit() is called
// on the thread (if the thread is the last thread in a daemon ThreadGroup the
// group should have the destroyed bit set before waiters are notified).
ensure_join(this);
...
}
static void ensure_join(JavaThread* thread) {
// We do not need to grap the Threads_lock, since we are operating on ourself.
Handle threadObj(thread, thread->threadObj());
assert(threadObj.not_null(), "java thread object must exist");
ObjectLocker lock(threadObj, thread);
// Ignore pending exception (ThreadDeath), since we are exiting anyway
thread->clear_pending_exception();
// Thread is exiting. So set thread_status field in java.lang.Thread class to TERMINATED.
java_lang_Thread::set_thread_status(threadObj(), java_lang_Thread::TERMINATED);
// Clear the native thread instance - this makes isAlive return false and allows the join()
// to complete once we've done the notify_all below
java_lang_Thread::set_thread(threadObj(), NULL);
lock.notify_all(thread);
// Ignore pending exception (ThreadDeath), since we are exiting anyway
thread->clear_pending_exception();
}