java并发:join源码分析

待我称王封你为后i 2021-11-01 09:42 277阅读 0赞

# join #

## join ##

join是Thread方法，它的作用是A线程中子线程B在运行之后调用了B.join()，A线程会阻塞直至B线程执行结束

## join源码(只有继承Thread类才能使用) ##

基于openjdk1.8的源码

public final void join() throws InterruptedException { join(0); } public final synchronized void join(long millis) throws InterruptedException { long base = System.currentTimeMillis(); long now = 0; if (millis < 0) { throw new IllegalArgumentException("timeout value is negative"); } if (millis == 0) { while (isAlive()) { wait(0); } } else { while (isAlive()) { long delay = millis - now; if (delay <= 0) { break; } wait(delay); now = System.currentTimeMillis() - base; } } } /** * Tests if this thread is alive. A thread is alive if it has * been started and has not yet died. * * @return <code>true</code> if this thread is alive; * <code>false</code> otherwise. */ public final native boolean isAlive(); /* <p> * Note that the {@code wait} method, as it places the current thread * into the wait set for this object, unlocks only this object; any * other objects on which the current thread may be synchronized remain * locked while the thread waits. * <p> ... */ public final native void wait(long timeout) throws InterruptedException;

## 源码分析 ##

A线程调用了B.join(),获取了B的锁，当B alive，B.wait(0)会让当前线程A阻塞，执行join方法等同于，A线程进入了下列  
的语句

syncronized(B){
    ...
    B.wait
    ...
    }

## 代码测试 ##

package com.java.javabase.thread.base; import lombok.extern.slf4j.Slf4j; @Slf4j public class JoinTest { public static void main(String[] args) { Thread t1 =new ThreadOne("t1"); t1.start(); log.info("current thread is : {} run",Thread.currentThread().getName()); try { t1.join(); } catch (InterruptedException e) { log.info("InterruptedException",e); e.printStackTrace(); } log.info("current thread is : {} end",Thread.currentThread().getName()); } static class ThreadOne extends Thread{ public ThreadOne(String name){ super(name); } @Override public void run(){ log.info("current thread is : {} start",Thread.currentThread().getName()); for(int i =0;i<10;i++) { log.info("current thread is : {} run",Thread.currentThread().getName()); } log.info("current thread is : {} end",Thread.currentThread().getName()); } } }

## 说明 ##

主线程调用t1.join之后，主线程只有t1的锁进入阻塞状态

## 运行结果 ##

2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 start
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 run
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 run
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 run
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 run
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 run
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 run
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 run
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 run
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 run
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 run
    2019-07-29 20:14:21,551   [t1] INFO  JoinTest  - current thread is : t1 end
    2019-07-29 20:14:21,551   [main] INFO  JoinTest  - current thread is : main run
    2019-07-29 20:14:21,551   [main] INFO  JoinTest  - current thread is : main end

转载于:https://www.cnblogs.com/JuncaiF/p/11269934.html