JVMTI SuspendThread和Javas thread.suspend有什么区别? [英] What is the difference between JVMTI SuspendThread and Javas thread.suspend?

问题描述

使用 SuspendThread 来自JVMTI代理，并使用普通Java

Is there any difference in using SuspendThread from a JVMTI agent and using the plain Java thread.suspend()?

推荐答案

在HotSpot JVM中，两个API的作用相同.

In HotSpot JVM both APIs have the same effect.

我已将链接添加到OpenJDK源代码的相关部分.这两个函数几乎互相复制粘贴，最终都调用相同的低级例程

I've added the links to the relevant parts of OpenJDK source code. Both functions are almost copy-paste of each other, both of them end up calling the same low-level routine JavaThread::java_suspend().

java.lang.Thread.suspend0()的本地代码:

The native code for java.lang.Thread.suspend0():

JVM_ENTRY(void, JVM_SuspendThread(JNIEnv* env, jobject jthread))
  JVMWrapper("JVM_SuspendThread");

  ThreadsListHandle tlh(thread);
  JavaThread* receiver = NULL;
  bool is_alive = tlh.cv_internal_thread_to_JavaThread(jthread, &receiver, NULL);
  if (is_alive) {
    // jthread refers to a live JavaThread.
    {
      MutexLockerEx ml(receiver->SR_lock(), Mutex::_no_safepoint_check_flag);
      if (receiver->is_external_suspend()) {
        // Don't allow nested external suspend requests. We can't return
        // an error from this interface so just ignore the problem.
        return;
      }
      if (receiver->is_exiting()) { // thread is in the process of exiting
        return;
      }
      receiver->set_external_suspend();
    }

    // java_suspend() will catch threads in the process of exiting
    // and will ignore them.
    receiver->java_suspend();

    // It would be nice to have the following assertion in all the
    // time, but it is possible for a racing resume request to have
    // resumed this thread right after we suspended it. Temporarily
    // enable this assertion if you are chasing a different kind of
    // bug.
    //
    // assert(java_lang_Thread::thread(receiver->threadObj()) == NULL ||
    //   receiver->is_being_ext_suspended(), "thread is not suspended");
  }
JVM_END

TI SuspendThread的实现:

jvmtiError
JvmtiEnv::SuspendThread(JavaThread* java_thread) {
  // don't allow hidden thread suspend request.
  if (java_thread->is_hidden_from_external_view()) {
    return (JVMTI_ERROR_NONE);
  }

  {
    MutexLockerEx ml(java_thread->SR_lock(), Mutex::_no_safepoint_check_flag);
    if (java_thread->is_external_suspend()) {
      // don't allow nested external suspend requests.
      return (JVMTI_ERROR_THREAD_SUSPENDED);
    }
    if (java_thread->is_exiting()) { // thread is in the process of exiting
      return (JVMTI_ERROR_THREAD_NOT_ALIVE);
    }
    java_thread->set_external_suspend();
  }

  if (!JvmtiSuspendControl::suspend(java_thread)) {
    // the thread was in the process of exiting
    return (JVMTI_ERROR_THREAD_NOT_ALIVE);
  }
  return JVMTI_ERROR_NONE;
} /* end SuspendThread */


bool JvmtiSuspendControl::suspend(JavaThread *java_thread) {
  // external suspend should have caught suspending a thread twice

  // Immediate suspension required for JPDA back-end so JVMTI agent threads do
  // not deadlock due to later suspension on transitions while holding
  // raw monitors.  Passing true causes the immediate suspension.
  // java_suspend() will catch threads in the process of exiting
  // and will ignore them.
  java_thread->java_suspend();

  // It would be nice to have the following assertion in all the time,
  // but it is possible for a racing resume request to have resumed
  // this thread right after we suspended it. Temporarily enable this
  // assertion if you are chasing a different kind of bug.
  //
  // assert(java_lang_Thread::thread(java_thread->threadObj()) == NULL ||
  //   java_thread->is_being_ext_suspended(), "thread is not suspended");

  ...

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