java - 当我调用 Thread.start() 时，如何调用 run() 方法？

Question

这个问题已经有答案了:

Which method calls run()? (1 个回答)

已关闭 3 年前。

尽管有多个帖子解释了为什么我们应该调用 start()方法而不是 run()直接方法我的疑问更像是JDK如何调用run()当我调用 start() 时内部方法？

我浏览了Thread类文件，我找不到 run()方法被调用。它是从 native 代码调用的吗？这是怎么发生的？

public synchronized void start() {
        /**
         * This method is not invoked for the main method thread or "system"
         * group threads created/set up by the VM. Any new functionality added
         * to this method in the future may have to also be added to the VM.
         *
         * A zero status value corresponds to state "NEW".
         */
        if (threadStatus != 0)
            throw new IllegalThreadStateException();

        /* Notify the group that this thread is about to be started
         * so that it can be added to the group's list of threads
         * and the group's unstarted count can be decremented. */
        group.add(this);

        boolean started = false;
        try {
            start0();
            started = true;
        } finally {
            try {
                if (!started) {
                    group.threadStartFailed(this);
                }
            } catch (Throwable ignore) {
                /* do nothing. If start0 threw a Throwable then
                  it will be passed up the call stack */
            }
        }
    }

Answer 1

由于 OpenJDK 是开源软件，因此您可以看到 native 代码源。

例如Github mirror of Thread.c类将 Thread.start0() native 方法定义为:

"start0",           "()V",        (void *)&JVM_StartThread},

其中 JVM_StartThread 定义于 jvm.cpp源文件。

如果您深入研究特定于操作系统的线程创建，您将到达 thread_entry()从 native 代码中调用 Thread.run() 方法的函数:

static void thread_entry(JavaThread* thread, TRAPS) {
  HandleMark hm(THREAD);
  Handle obj(THREAD, thread->threadObj());
  JavaValue result(T_VOID);
  JavaCalls::call_virtual(&result,
                          obj,
                          SystemDictionary::Thread_klass(),
                          vmSymbols::run_method_name(),
                          vmSymbols::void_method_signature(),
                          THREAD);
}