我需要一次执行一定数量的任务4，就像这样:
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
while(...) {
taskExecutor.execute(new MyTask());
}
//...wait for completion somehow
当所有这些都完成后，我如何得到通知?现在我想不出比设置一些全局任务计数器更好的方法，并在每个任务结束时减少它，然后在无限循环中监视这个计数器变成0;或获取一个期货列表，并在无限循环监视器isDone为所有它们。不涉及无限循环的更好的解决方案是什么?
谢谢。
当前回答
使用CountDownLatch:
CountDownLatch latch = new CountDownLatch(totalNumberOfTasks);
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
while(...) {
taskExecutor.execute(new MyTask());
}
try {
latch.await();
} catch (InterruptedException E) {
// handle
}
在任务中(在try / finally中附上)
latch.countDown();
其他回答
使用CountDownLatch:
CountDownLatch latch = new CountDownLatch(totalNumberOfTasks);
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
while(...) {
taskExecutor.execute(new MyTask());
}
try {
latch.await();
} catch (InterruptedException E) {
// handle
}
在任务中(在try / finally中附上)
latch.countDown();
这可能会有所帮助
Log.i(LOG_TAG, "shutting down executor...");
executor.shutdown();
while (true) {
try {
Log.i(LOG_TAG, "Waiting for executor to terminate...");
if (executor.isTerminated())
break;
if (executor.awaitTermination(5000, TimeUnit.MILLISECONDS)) {
break;
}
} catch (InterruptedException ignored) {}
}
只是在这里提供更多不同于使用闩锁/屏障的选择。 你也可以在它们全部使用完CompletionService之前得到部分结果。
来自Java并发实践: “如果您有一批计算要提交给Executor，并且您希望检索它们的结果 可用时，您可以保留与每个任务关联的Future，并通过调用get来重复轮询完成 超时为0。这是可能的，但很乏味。幸运的是，还有更好的方法:完井服务。”
这里是实现
public class TaskSubmiter {
private final ExecutorService executor;
TaskSubmiter(ExecutorService executor) { this.executor = executor; }
void doSomethingLarge(AnySourceClass source) {
final List<InterestedResult> info = doPartialAsyncProcess(source);
CompletionService<PartialResult> completionService = new ExecutorCompletionService<PartialResult>(executor);
for (final InterestedResult interestedResultItem : info)
completionService.submit(new Callable<PartialResult>() {
public PartialResult call() {
return InterestedResult.doAnOperationToGetPartialResult();
}
});
try {
for (int t = 0, n = info.size(); t < n; t++) {
Future<PartialResult> f = completionService.take();
PartialResult PartialResult = f.get();
processThisSegment(PartialResult);
}
}
catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
catch (ExecutionException e) {
throw somethinghrowable(e.getCause());
}
}
}
基本上在ExecutorService上调用shutdown()，然后调用awaitterminate ():
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
while(...) {
taskExecutor.execute(new MyTask());
}
taskExecutor.shutdown();
try {
taskExecutor.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
} catch (InterruptedException e) {
...
}
ExecutorService WORKER_THREAD_POOL
= Executors.newFixedThreadPool(10);
CountDownLatch latch = new CountDownLatch(2);
for (int i = 0; i < 2; i++) {
WORKER_THREAD_POOL.submit(() -> {
try {
// doSomething();
latch.countDown();
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
});
}
// wait for the latch to be decremented by the two remaining threads
latch.await();
如果doSomething()抛出一些其他异常，latch.countDown()似乎不会执行，那么我该怎么办?
