In a multi-threaded java program, what happens if a thread object T has been instantiated, and then has T.join() called before the thread has started? Assume that some other thread could call T.start() at any time after T has been instantiated, either before or after another thread calls T.join().
在多线程java程序中，如果一个线程对象T被实例化，然后在线程启动之前调用T.join()，会发生什么?假设其他一些线程可以在实例化T之后的任何时间调用T.start()，或者在另一个线程调用T.join()之前或者之后。
I'm asking because I think I have a problem where T.join() has been called before T.start(), and the thread calling T.join() hangs.
我这样问是因为我认为我有一个问题，在T.start()之前调用了.join()，而调用.join()的线程挂起了。
Yes, I know I have some design problems that, if fixed, could make this a non-issue. However, I would like to know the specifics of the join() behavior, because the only thing the Java API docs say is "Waits for this thread to die."
是的，我知道我有一些设计问题，如果解决了，就不会有问题了。但是，我想知道join()行为的具体情况，因为Java API文档只说“等待这个线程死掉”。
1 个解决方案
#1
12
It will just return. See code below - isAlive() will be false before the thread starts, so nothing will happen.
它只会返回。请参见下面的代码- isAlive()将在线程开始之前为false，因此不会发生任何事情。
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;
}
}
}
The code snippet is © Copyright Oracle 2006 and/or its affiliates, and can be found here. Licensed under Java Research License.
甲骨文版权©2006的代码片段和/或其附属公司,并可以在这里找到。获得Java研究许可。
#1
12
It will just return. See code below - isAlive() will be false before the thread starts, so nothing will happen.
它只会返回。请参见下面的代码- isAlive()将在线程开始之前为false，因此不会发生任何事情。
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;
}
}
}
The code snippet is © Copyright Oracle 2006 and/or its affiliates, and can be found here. Licensed under Java Research License.
甲骨文版权©2006的代码片段和/或其附属公司,并可以在这里找到。获得Java研究许可。