java线程运行机制初探

创建线程demo

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public static void main(String[] args) throws InterruptedException {

	Thread thread = new Thread(() -> {
	
		System.out.println("搵食艰难");
	
	});
	
	thread.start();

}

启动线程：start方法

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public synchronized void start() {
        ...
        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 */
            }
        }
    }

随后调用start0()方法，这是一个jvm本地方法，最终是通过操作系统来创建线程，关键代码在 os_bsd.cpp文件(笔者用的mac调试jvm源码，Windows是os_windows.cpp)

avatar

ThreadState state; 就是定义了线程的状态(面试偶尔会问线程流转状态o(╯□╰)o，要记记)，是通过c的枚举标识的：

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enum ThreadState {
  ALLOCATED,                    // Memory has been allocated but not initialized
  INITIALIZED,                  // The thread has been initialized but yet started
  RUNNABLE,                     // Has been started and is runnable, but not necessarily running
  MONITOR_WAIT,                 // Waiting on a contended monitor lock
  CONDVAR_WAIT,                 // Waiting on a condition variable
  OBJECT_WAIT,                  // Waiting on an Object.wait() call
  BREAKPOINTED,                 // Suspended at breakpoint
  SLEEPING,                     // Thread.sleep()
  ZOMBIE                        // All done, but not reclaimed yet
};

有没有觉得有点眼熟~ 最关键的步骤是通过操作系统函数创建系统线程：

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int ret = pthread_create(&tid, &attr, (void* (*)(void*)) java_start, thread);

pthread_create参数含义：

  • 第一个参数：新创建的线程ID指向的内存单元
  • 第二个参数：线程属性
  • 第三个参数：新创建的线程从start_rtn函数的地址开始运行
  • 第四个参数： 若上述函数需要参数，将参数放入结构中并将地址作为arg传入