使用Java中的CompletableFuture并行执行for循环并记录执行

问题描述

我有一个for循环，我正在尝试使用CompletableFuture进行并行化.

I have a for loop which I am trying to parallelize using CompletableFuture.

for (int i = 0; i < 10000; i++) {
    doSomething();
    doSomethingElse();
}

到目前为止，我所拥有的是:

What I have till now is:

for (int i = 0; i < 10000; i++) {
    CompletableFuture.runAsync(() -> doSomething());
    CompletableFuture.runAsync(() -> doSomethingElse());
}

我想这可以达到目的，但是在所有处理的开始和结束之前都需要打印日志.如果我这样做:

I guess this serves the purpose but there is a requirement to print log just before the start and end of all the processing. If I do this:

log("Started doing things");
for (int i = 0; i < 10000; i++) {
    CompletableFuture.runAsync(() -> doSomething());
    CompletableFuture.runAsync(() -> doSomethingElse());
}
log("Ended doing things");

这是否保证一旦所有for循环结束后第二个日志语句将被打印，因为它是在单独的线程中执行的?如果没有，有没有办法在不阻塞主线程的情况下做到这一点?

Does this guarantee that the second log statement will be printed once all the for loop is over since that is executing in a separate thread? If not, is there a way to do this without blocking the main thread?

推荐答案

您必须收集所有CompletableFuture，然后等待其完成:

You have to collect all CompletableFutures and wait for their complete:

log("Started doing things");
List<CompletableFuture> futures = new ArrayList();
for (int i = 0; i < 10000; i++) {
    futures.add(CompletableFuture.runAsync(() -> doSomething()));
    futures.add(CompletableFuture.runAsync(() -> doSomethingElse()));
}
CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]))
                 .thenRunAsync(() -> log("Ended doing things"));

或者当您使用ExecutorService时:

Or when you use the ExecutorService:

CompletableFuture.runAsync(() -> {
    try {
        executorService.invokeAll(tasks);
    } catch (InterruptedException) {
        e.printStackTrace();
    }
    log("Ended doing things");
});

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