在ExecutorService中捕获所有期货/可赎回债券的异常

Question

I have an ExecutorService containing a number of running Callables . I have a list of Futures for these Callables . I want to find out as soon as possible if one of the Callables throws an Exception . All Callables are equally likely to throw an Exception . The Callables usually run for several hours.

The usual approach seems to be to use the Future.get() method. However, you can only use this for one Future . If another Future throws an Exception I am not notified. So I was thinking of writing a loop that checks the Future.isDone() method for all Futures and sleeping for some time after each iteration. However, this approach is not really nice, so I was wondering if there is a better way of doing this?

Answer 1

You should use an ExecutorCompletionService , wrap your executor with it and then calling #take() will return the first completed result.

Example:

CompletionService<Object> completionService = new ExecutorCompletionService<>(executor);
//submit a bunch of tasks
IntStream.range(0, 100).forEach(i-> completionService.submit(Object::new));
//Wait for any of them to complete, wrap in a loop to take them all
completionService.take();

Answer 2

You can use CompletableFuture for your use-case

static CompletableFuture<Object> anyOf(CompletableFuture<?>... cfs)

Returns a new CompletableFuture that is completed when any of the given CompletableFutures complete, with the same result. Otherwise, if it completed exceptionally, the returned CompletableFuture also does so, with a CompletionException holding this exception as its cause. If no CompletableFutures are provided, returns an incomplete CompletableFuture.

You should store all your futures in a list. `

Now

List<CompletableFuture<?>> futureList = // all futures;
while(futureList.size()>0){
    CompletableFuture<?> completed = CompletableFuture.anyOf(futureList); //convert futureList to array
    if(completed.isCompletedExceptionally()){
       // first future that completed with an exception
    }else{
       //future completed without exception, store the result or process
       futureList.remove(completed); // remove it from the incomplete list
    }
}

You may obtain a CompletableFuture like

final CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
         //...long running...
         return "returnVal";
      },
   executor); //here executor is your executor pool

If you don't want to use explicit executor pool

    final CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
             //...long running...
             return "returnVal";
          });

However, in this case it will be submitted to the ForkJoinPool .commonPool()