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[英]Thread.start() throwing exception after Thread.isAlive() check
[英]Do I need to check for Thread.isAlive() here?
在Web控制器中,我有一个接收请求的父线程。 有些请求需要很长时间才能处理。 为了防止客户端超时,我设置父线程每2秒发送一个字节,而子线程正在执行耗时的操作部分。
我想确保我考虑到子线程死亡的所有可能情况,但我也不想进行任何无关的检查。
这是父线程:
// This is my runnable class
ProcessorRunnable runnable = new ProcessorRunnable(settings, Thread.currentThread());
Thread childThread = new Thread(runnable);
childThread.start();
boolean interrupted = false;
while (!runnable.done) { // <-- Check in question
outputStream.write(' ');
outputStream.flush();
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
// If the runnable is done, then this was an expected interrupt
// Otherwise, remember the interruption and re-interrupt after processing is done
// Or with self so that a later expected interrupt won't clear out an earlier unexpected one
interrupted = interrupted || !runnable.done;
}
}
if (runnable.runtimeException != null) {
LOG.error("Propagating runtime exception from thread");
throw runnable.runtimeException;
}
// ... Further processing on the results provided by the child thread
这里是ProcessorRunnable:
private volatile boolean done;
private volatile Result result;
private volatile RuntimeException runtimeException;
// ...
public void run() {
done = false;
try {
result = myService.timeConsumingOperation(settings);
} catch (RuntimeException e) {
runtimeException = e;
} finally {
done = true;
parentThread.interrupt();
}
}
我的问题是,在父线程的主循环中添加&& Thread.isAlive()
检查会给我带来什么吗? 似乎在finally
块中设置done = true
应该可以解决问题,但是在某些情况下,这个子线程可能会死而不通知父级吗?
子线程中的finally
将始终在完成之前执行。 即使该线程被中断或停止,这也会发生异常,它会使调用堆栈冒泡并finally
触发所有s。 因此,如果子线程被中断,则done
将始终为true。
对于像这样的后台任务,您可能希望使用ExecutorService
而不是原始线程。 您可以向ExecutorService
提交Runnable
,并在返回的future上调用get()
直到它完成为止。 如果要在等待时打印出空格,可以使用循环,以超时方式调用get()
版本。
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