Java线程的start方法回调run方法的操作技巧

class MyThread extends Thread{ 
 public void run() { 
  System.out.println("My thread is started."); 
 } 
}

MyThread myThread = new MyThread(); 
myThread.start();

class MyRunnable implements Runnable{ 
 public void run() { 
  System.out.println("My runnable is invoked."); 
 } 
}

Thread myThread = new Thread( new MyRunnable()); 
myThread.start();

public synchronized void start() { 
 …
 start0(); 
 …
}

private native void start0();

private static native void registerNatives(); 
static{ 
 registerNatives(); 
}

JNIEXPORT void JNICALL 
Java_Java_lang_Thread_registerNatives (JNIEnv *env, jclass cls){ 
 (*env)->RegisterNatives(env, cls, methods, ARRAY_LENGTH(methods)); 
} 
static JNINativeMethod methods[] = { 
 {"start0", "()V",(void *)&JVM_StartThread}, 
 {"stop0", "(" OBJ ")V", (void *)&JVM_StopThread}, 
 {"isAlive","()Z",(void *)&JVM_IsThreadAlive}, 
 {"suspend0","()V",(void *)&JVM_SuspendThread}, 
 {"resume0","()V",(void *)&JVM_ResumeThread}, 
 {"setPriority0","(I)V",(void *)&JVM_SetThreadPriority}, 
 {"yield", "()V",(void *)&JVM_Yield}, 
 {"sleep","(J)V",(void *)&JVM_Sleep}, 
 {"currentThread","()" THD,(void *)&JVM_CurrentThread}, 
 {"countStackFrames","()I",(void *)&JVM_CountStackFrames}, 
 {"interrupt0","()V",(void *)&JVM_Interrupt}, 
 {"isInterrupted","(Z)Z",(void *)&JVM_IsInterrupted}, 
 {"holdsLock","(" OBJ ")Z",(void *)&JVM_HoldsLock}, 
 {"getThreads","()[" THD,(void *)&JVM_GetAllThreads}, 
 {"dumpThreads","([" THD ")[[" STE, (void *)&JVM_DumpThreads}, 
};

JVM_ENTRY(void, JVM_StartThread(JNIEnv* env, jobject jthread)) 
 …
 native_thread = new JavaThread(&thread_entry, sz);

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

class vmSymbolHandles: AllStatic { 
 …
 template(run_method_name,"run") 
 …
}

package com.ljq.test;
public class ThreadTest {
  /**
   * 观察直接调用run()和用start()启动一个线程的差别 
   * 
   * @param args
   * @throws Exception
   */
  public static void main(String[] args){
    Thread thread=new ThreadDemo();
    //第一种
    //表明: run()和其他方法的调用没任何不同,main方法按顺序执行了它,并打印出最后一句
    //thread.run();
    //第二种
    //表明: start()方法重新创建了一个线程,在main方法执行结束后,由于start()方法创建的线程没有运行结束,
    //因此主线程未能退出,直到线程thread也执行完毕.这里要注意,默认创建的线程是用户线程(非守护线程)
    //thread.start();
    //第三种
    //1、为什么没有打印出100句呢?因为我们将thread线程设置为了daemon(守护)线程,程序中只有守护线程存在的时候,是可以退出的,所以只打印了七句便退出了
    //2、当java虚拟机中有守护线程在运行的时候，java虚拟机会关闭。当所有常规线程运行完毕以后，
    //守护线程不管运行到哪里，虚拟机都会退出运行。所以你的守护线程最好不要写一些会影响程序的业务逻辑。否则无法预料程序到底会出现什么问题
    //thread.setDaemon(true);
    //thread.start();
    //第四种
    //用户线程可以被System.exit(0)强制kill掉,所以也只打印出七句
    thread.start();
    System.out.println("main thread is over");
    System.exit(1);
  }
  public static class ThreadDemo extends Thread{
    @Override
    public void run() {
      for (int i = 0; i < 100; i++) {
        System.out.println("This is a Thread test"+i);
      }
    }
  }
}