共同学习Java源代码-多线程与并发-AbstractExecutorService类(三)

最新推荐文章于 2022-07-22 13:04:42 发布

原创最新推荐文章于 2022-07-22 13:04:42 发布 · 198 阅读

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本文解析了 ExecutorService 接口中的 invokeAll 方法，包括无时间限制与带时间限制两个版本，介绍了如何提交多个 Callable 任务，并等待它们全部完成。

public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
throws InterruptedException {
if (tasks == null)
throw new NullPointerException();
ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
boolean done = false;
try {
for (Callable<T> t : tasks) {
RunnableFuture<T> f = newTaskFor(t);
futures.add(f);
execute(f);
}
for (int i = 0, size = futures.size(); i < size; i++) {
Future<T> f = futures.get(i);
if (!f.isDone()) {
try {
f.get();
} catch (CancellationException ignore) {
} catch (ExecutionException ignore) {
}
}
}
done = true;
return futures;
} finally {
if (!done)
for (int i = 0, size = futures.size(); i < size; i++)
futures.get(i).cancel(true);
}
}

这个方法是调用所有任务的方法

判断参数任务集合如果为空就抛出异常

创建一个ArrayList长度为参数集合的长度名为futures

创建布尔变量done为false

遍历参数任务集合将所有任务包装成RunnableFuture 然后添加进futures 然后执行RunnableFuture任务

然后遍历futures 挨个取出刚才的任务

判断每个任务如果没有完成就再次调用get方法

跳出循环后将done设为true

返回futures

在finally块中如果done还是false 就遍历所有任务并调用cancel方法结束任务

public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
long timeout, TimeUnit unit)
throws InterruptedException {
if (tasks == null)
throw new NullPointerException();
long nanos = unit.toNanos(timeout);
ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
boolean done = false;
try {
for (Callable<T> t : tasks)
futures.add(newTaskFor(t));

final long deadline = System.nanoTime() + nanos;
final int size = futures.size();

// Interleave time checks and calls to execute in case
// executor doesn't have any/much parallelism.
for (int i = 0; i < size; i++) {
execute((Runnable)futures.get(i));
nanos = deadline - System.nanoTime();
if (nanos <= 0L)
return futures;
}

for (int i = 0; i < size; i++) {
Future<T> f = futures.get(i);
if (!f.isDone()) {
if (nanos <= 0L)
return futures;
try {
f.get(nanos, TimeUnit.NANOSECONDS);
} catch (CancellationException ignore) {
} catch (ExecutionException ignore) {
} catch (TimeoutException toe) {
return futures;
}
nanos = deadline - System.nanoTime();
}
}
done = true;
return futures;
} finally {
if (!done)
for (int i = 0, size = futures.size(); i < size; i++)
futures.get(i).cancel(true);
}

}

这个方法和上面的类似就是加上了截止时间

AbstractExecutorService讲解完毕