java Thread源码分析

一、使用 java 多线程

java多线程其中两种使用方式：

1、继承 Thread 类

2、实现 Runnable 接口

 public class ThreadTest {
     public static void main(String[] args) {
         Thread t1 = new MyThread("thread-0001");
         t1.start();
         MyRunnable mr = new MyRunnable();
         Thread t2 = new Thread(mr, "thread-0002");
         t2.start();
     }
     private static class MyThread extends Thread{
         public MyThread(String name) {
             this.setName(name);
         }
         @Override
         public void run() {
             System.out.println(this.getName()+" thread run....");
         }
     }
     private static class MyRunnable implements Runnable{
         @Override
         public void run() {
             System.out.println(Thread.currentThread().getName()+" runable run....");
         }
     }
 }

二、线程初始化

　　继承 Thread 和 实现 Runnable 的方式都要经过初始化Thread构造函数的方式设置相关参数的过程。

　　构造函数如下：

public Thread() {
    init(null, null, "Thread-" + nextThreadNum(), 0);
}

public Thread(Runnable target) {
    init(null, target, "Thread-" + nextThreadNum(), 0);
}

public Thread(ThreadGroup group, Runnable target) {
    init(group, target, "Thread-" + nextThreadNum(), 0);
}

public Thread(String name) {
    init(null, null, name, 0);
}

public Thread(ThreadGroup group, String name) {
    init(group, null, name, 0);
}

public Thread(Runnable target, String name) {
    init(null, target, name, 0);
}

public Thread(ThreadGroup group, Runnable target, String name) {
    init(group, target, name, 0);
}

public Thread(ThreadGroup group, Runnable target, String name, long stackSize) {
    init(group, target, name, stackSize);
}

　　上述构造函数涉及的参数：

　　ThreadGroup group（该线程所属线程组）、Runnable targer、String name（线程名）、long stackSize（线程堆栈大小，不知道有什么作用，日后再填坑）。

　　最终会执行 init 函数：

 private void init(ThreadGroup g, Runnable target, String name,
                       long stackSize, AccessControlContext acc,
                       boolean inheritThreadLocals) {
         if (name == null) {
             throw new NullPointerException("name cannot be null");
         }

         // 线程名
         this.name = name;

         // 创建该线程时的线程（即父线程）
         Thread parent = currentThread();
         SecurityManager security = System.getSecurityManager();
         // 线程组
         if (g == null) {
             /* Determine if it's an applet or not */

             /* If there is a security manager, ask the security manager
                what to do. */
             if (security != null) {
                 g = security.getThreadGroup();
             }

             /* If the security doesn't have a strong opinion of the matter
                use the parent thread group. */
             // 没有设置线程组时，默认线程组为父线程的线程组
             if (g == null) {
                 g = parent.getThreadGroup();
             }
         }

         /* checkAccess regardless of whether or not threadgroup is
            explicitly passed in. */
         g.checkAccess();

         /*
          * Do we have the required permissions?
          */
         if (security != null) {
             if (isCCLOverridden(getClass())) {
                 security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
             }
         }

         g.addUnstarted();

         // 设置线程组
         this.group = g;
         // 设置
         this.daemon = parent.isDaemon();
         // 设置优先级和父线程的优先级相同
         this.priority = parent.getPriority();
         if (security == null || isCCLOverridden(parent.getClass()))
             this.contextClassLoader = parent.getContextClassLoader();
         else
             this.contextClassLoader = parent.contextClassLoader;
         this.inheritedAccessControlContext =
                 acc != null ? acc : AccessController.getContext();
         // Runnable target
         this.target = target;
         setPriority(priority);
         if (inheritThreadLocals && parent.inheritableThreadLocals != null)
             this.inheritableThreadLocals =
                 ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
         /* Stash the specified stack size in case the VM cares */
         this.stackSize = stackSize;

         /* Set thread ID */
         // 设置线程的ID（threadSeqNumber），同步递增，每个线程都会生成一个thread ID
         // 另外一个同步递增的ID (threadInitNumber)，这个在没有显式指定线程名的时候，默认生成线程名（Thread-N）。
         // 所以，threadSeqNumber >= threadInitNumber
         tid = nextThreadID();
     }

　　t1.start()会调用本地方法start0()启动线程：

 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. */
         // 将线程添加到线程组中
          group.add(this);

         boolean started = false;
         try {
             // navite修饰的方法
             start0();
             started = true;
         } finally {
             try {
                 if (!started) {
                     // 线程启动失败，从线程组中移除线程
                     group.threadStartFailed(this);
                 }
             } catch (Throwable ignore) {
                 /* do nothing. If start0 threw a Throwable then
                   it will be passed up the call stack */
             }
         }
     }