JVM_ENTRY(void, JVM_StartThread(JNIEnv* env, jobject jthread))

  {- -------------------------------------------
  (1) (トレース出力) (See: JVMWrapper)
      ---------------------------------------- -}

      JVMWrapper("JVM_StartThread");

  {- -------------------------------------------
  (1) (変数宣言など)
      ---------------------------------------- -}

      JavaThread *native_thread = NULL;

      // We cannot hold the Threads_lock when we throw an exception,
      // due to rank ordering issues. Example:  we might need to grab the
      // Heap_lock while we construct the exception.
      bool throw_illegal_thread_state = false;

  {- -------------------------------------------
  (1) 新しい JavaThread オブジェクトを生成し, JavaThread::prepare() で初期化を行う.
      (ただし, 対象の java.lang.Thread オブジェクトの状態がおかしい場合は, どちらも行わない)
      (また, JavaThread オブジェクトの生成に失敗した場合は, JavaThread::prepare() の呼び出しは行わない)
      ---------------------------------------- -}

      // We must release the Threads_lock before we can post a jvmti event
      // in Thread::start.
      {
        // Ensure that the C++ Thread and OSThread structures aren't freed before
        // we operate.
        MutexLocker mu(Threads_lock);

        // Since JDK 5 the java.lang.Thread threadStatus is used to prevent
        // re-starting an already started thread, so we should usually find
        // that the JavaThread is null. However for a JNI attached thread
        // there is a small window between the Thread object being created
        // (with its JavaThread set) and the update to its threadStatus, so we
        // have to check for this
        if (java_lang_Thread::thread(JNIHandles::resolve_non_null(jthread)) != NULL) {
          throw_illegal_thread_state = true;
        } else {
          // We could also check the stillborn flag to see if this thread was already stopped, but
          // for historical reasons we let the thread detect that itself when it starts running

          jlong size =
                 java_lang_Thread::stackSize(JNIHandles::resolve_non_null(jthread));
          // Allocate the C++ Thread structure and create the native thread.  The
          // stack size retrieved from java is signed, but the constructor takes
          // size_t (an unsigned type), so avoid passing negative values which would
          // result in really large stacks.
          size_t sz = size > 0 ? (size_t) size : 0;
          native_thread = new JavaThread(&thread_entry, sz);

          // At this point it may be possible that no osthread was created for the
          // JavaThread due to lack of memory. Check for this situation and throw
          // an exception if necessary. Eventually we may want to change this so
          // that we only grab the lock if the thread was created successfully -
          // then we can also do this check and throw the exception in the
          // JavaThread constructor.
          if (native_thread->osthread() != NULL) {
            // Note: the current thread is not being used within "prepare".
            native_thread->prepare(jthread);
          }
        }
      }

  {- -------------------------------------------
  (1) 対象の java.lang.Thread オブジェクトの状態がおかしい場合は, 
      IllegalThreadStateException を出す (この場合はここで終了).
      ---------------------------------------- -}

      if (throw_illegal_thread_state) {
        THROW(vmSymbols::java_lang_IllegalThreadStateException());
      }

  {- -------------------------------------------
  (1) (assert)
      ---------------------------------------- -}

      assert(native_thread != NULL, "Starting null thread?");

  {- -------------------------------------------
  (1) JavaThread オブジェクトの生成に失敗していた場合は, OutOfMemoryError を出す.

      ついでに, (JVMTI のフック点)でもある.
      (See: JvmtiExport::post_resource_exhausted())
      ---------------------------------------- -}

      if (native_thread->osthread() == NULL) {
        // No one should hold a reference to the 'native_thread'.
        delete native_thread;
        if (JvmtiExport::should_post_resource_exhausted()) {
          JvmtiExport::post_resource_exhausted(
            JVMTI_RESOURCE_EXHAUSTED_OOM_ERROR | JVMTI_RESOURCE_EXHAUSTED_THREADS,
            "unable to create new native thread");
        }
        THROW_MSG(vmSymbols::java_lang_OutOfMemoryError(),
                  "unable to create new native thread");
      }

  {- -------------------------------------------
  (1) Thread::start() を呼んで, 生成した JavaThread を開始させる.
      ---------------------------------------- -}

      Thread::start(native_thread);

    JVM_END