使用Java CompletableFuture方法时的同步行为

Question

I am using Java's CompletableFuture like this into a spring boot @Service :

@Service
public class ProcessService {

    private static final ExecutorService EXECUTOR = Executors.newFixedThreadPool(3);

    @Autowired
    ChangeHistoryService changeHistoryService;

    public Attribute process(Attribute attribute) {
        //some code

        CompletableFuture.runAsync(() -> changeHistoryService.logChanges(attribute), EXECUTOR);

        return attribute;
    }

}

The process method is called form a method inside a @RestController :

@RestController
public class ProcessController {


    @Autowired
    ProcessService processService;

    @RequestMapping(value = "/processAttribute",
            method = {RequestMethod.POST},
            produces = {MediaType.APPLICATION_JSON_VALUE},
            consumes = {MediaType.APPLICATION_JSON_VALUE})
    public Attribute applyRules(@RequestBody Attribute attribute) {

        Attribute resultValue = processService.service(attribute);

        return resultValue;
    }

}

ChangeHistoryService::logChanges only save some data to database according to its parameter. I have a microservice that makes a number of request to this "/processAttribute" endpoint and print all responses.

When I put a breakpoint in logChanges method, the microservice is waiting on some request but not all which makes me think that the ChangeHistoryService::logChanges not always runs async. If I don't supply the runAsync with a ExecutorService, the microservice blocks on more request but still not all. From what I understood this is because method that process the request and logChanges method share same thread pool (ForkJoinPool?). Anyway, as I have another ExecutorService, logChanges should not runs independently? Or is something about how IDE treats breakpoints on async task? I am using IntelliJ IDEA.

Answer 1

The problem was that the breakpoint suspends all threads and not only the thread that runs logChanges method. I fix this in Intellij IDEA by pressing right click on breakpoint and checked "Thread" checkbox, not "All":

Answer 2

You have a rather small threadpool, so it's no wonder that you can saturate it. The threads that process requests are not the same as the ones processing your CompletableFutures . One is an internal component of the server, and the second one is the one you explicitly created, EXECUTOR .

If you want to increase the asynchronousness, try giving EXECUTOR some more threads and see how the behaviour changes accordingly. Currently the EXECUTOR is a bottleneck, since there are far more threads available for requests to run in.

Note that by putting a breakpoint inside logChanges() you'll be blocking one thread in the pool, making it even more saturated.