How to log completeOnTimeout of completable-future?

Question

I have a couple of completableFutures, with completeOnTimeout ( and return empty object in this case), for example:

return CompletableFuture.supplyAsync(() -> {
        try {
            log.info("#####Start sleeping");
            Thread.sleep(9000);
            log.info("#####Finished sleeping");
        } catch (InterruptedException e){
            log.info("#####Interrupted");
        }

        TestEntity reputationEntity = getTestEntity(destination);
        return getTestDTO(destination, accountId, testEntity);}).completeOnTimeout(new testDTO(), asyncTimeoutMls, TimeUnit.MILLISECONDS);

How do I add log the case of completeOnTimeout? Later in the code, I combine this c future with another one, by: CompletableFuture.allOf(test1ComletableFuture, test2ComletableFuture).join(); So I would like to know ( and log) when one of this feature completed on timeout. Something like lambda expression inside of completeOnTimeout?

Answer 1

According to completeOnTimeout implementation, there is no option to specify any code or logging, however it turns out completeOnTimeout under the hood just schedules a .complete() call via a ScheduledThreadPoolExecutor. So for me it seems absolutely ok to implement it by yourself. A brief example:

private final ScheduledThreadPoolExecutor futureCompleteExecutor = new ScheduledThreadPoolExecutor(1);

and then

    CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> "executed");

    futureCompleteExecutor.schedule(() -> {
        if (completableFuture.complete("timeouted")) {
            // log
        }
    }, 1, TimeUnit.MINUTES)

Extract a method to make usage smoothly. Don't execute blocking or long-running code in a scheduled task. Not a perfect, yet flexible approach.