现有线程threadone、threadtwo和threadthree,想要的运行顺序为threadone->threadtwo->threadthree,应该如何处理?这里需要用到一个简单的线程方法join().
join()方法的说明:join方法挂起当前调用线程,直到被调用线程完成后在继续执行(join() method suspends the execution of the calling thread until the object called finishes its execution).
下面看一个例子:
/**
* Thread one for test.
*/
public class ThreadOne implements Runnable {
@Override
public void run() {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + " start...");
System.out.println(threadName + " end.");
}
}
/**
* Thread two for test.
*/
public class ThreadTwo implements Runnable {
@Override
public void run() {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + " start...");
System.out.println(threadName + " end.");
}
}
/**
* Thread three for test.
*/
public class ThreadThree implements Runnable {
@Override
public void run() {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + " start...");
System.out.println(threadName + " end.");
}
}
public class JoinMainTest {
public static void main(String[] args) {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + " start...");
Thread firstThread = new Thread(new ThreadOne());
Thread secondThread = new Thread(new ThreadTwo());
Thread thirdThread = new Thread(new ThreadThree());
// 1. no order thread run
firstThread.start();
secondThread.start();
thirdThread.start();
System.out.println(threadName + " end.");
}
}
上面得到的结果如下:
/**
*
main start...
Thread-0 start...
main end.
Thread-0 end.
Thread-1 start...
Thread-1 end.
Thread-2 start...
Thread-2 end.
*/
public class JoinMainTest {
public static void main(String[] args) {
String threadName = Thread.currentThread().getName();
System.out.println(threadName + " start...");
Thread firstThread = new Thread(new ThreadOne());
Thread secondThread = new Thread(new ThreadTwo());
Thread thirdThread = new Thread(new ThreadThree());
// 2. thread run in order
try {
firstThread.start();
firstThread.join();
secondThread.start();
secondThread.join();
thirdThread.start();
thirdThread.join();
} catch (Exception ex) {
System.out.println("thread join exception.");
}
System.out.println(threadName + " end.");
}
}
这里得到的结果就是顺序执行的了:
/**
*
main start...
Thread-0 start...
Thread-0 end.
Thread-1 start...
Thread-1 end.
Thread-2 start...
Thread-2 end.
main end.
*/
再来看一下join()的源码,join()调用的就是join(0).可以看到,其实join就是wait,直到线程执行完成。
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;
}
}
}
转载于:https://my.oschina.net/secyaher/blog/274488