多執行緒中的join方法——原始碼分析
阿新 • • 發佈:2019-02-16
join方法的作用是等待執行緒銷燬,當主執行緒中呼叫了其他執行緒的join方法時,主執行緒需要等到該執行緒執行完畢才可以繼續執行,示例如下:
public class MyThread extends Thread
{
public void run()
{
try
{
int value = (int)(Math.random() * 10000);
System.out.println(value);
Thread.sleep(value);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
}
}
public static void main(String[] args) throws Exception
{
MyThread mt = new MyThread();
mt.start();
mt.join();
System.out.println("主執行緒");
}
另外join方法與wait方法一樣,也是在阻塞時需要釋放鎖,原因是join方法的實現中呼叫了wait方法,原始碼如下:
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;
}
}
}