java.util.concurrent

问题 After spending the day of learning about the java Concurrency API, I still dont quite get how could I create the following functionality with the help of CompletableFuture and ExecutorService classes: When I get a request on my REST endpoint I need to: Start an asynchronous task (includes DB query, filtering, etc.), which will give me a list of String URLs at the end In the meanwhile, responde back to the REST caller with HTTP OK, that the request was received, I'm working on it When the

问题 I need a HashMap that is accessible from multiple threads. There are two simple options, using a normal HashMap and synchronizing on it or using a ConcurrentHashMap. Since ConcurrentHashMap does not block on read operations it seems much better suited for my needs (almost exclusively reads, almost never updates). On the other hand, I expect very low concurrency anyway, so there should be no blocking (just the cost of managing the lock). The Map will also be very small (under ten entries), if

问题 Well the title basically says it all, with the small addition that I would really like to know when to use them. And it might be simple enough - I've read the documentation for them both, still can't tell the difference much. There are answers like this here that basically say: Yielding also was useful for busy waiting... I can't agree much with them for the simple reason that ForkJoinPool uses Thread::yield internally and that is a pretty recent addition in the jdk world. The thing that

问题 I'm trying to implement a sample application to test Callable and ExecutorService interfaces. In my app I have: @Bean("fixedThreadPool") public ExecutorService fixedThreadPool() { return Executors.newFixedThreadPool(5); } Then: public void removeUserIds(Set<String> userIds) { UriComponentsBuilder builder = UriComponentsBuilder.fromUriString("http://localhost:8080/remove"); final List<Callable<String>> callables = new ArrayList<>(); userIds.forEach(userId -> { final Callable<String> task = ()

问题 Our application has some code that runs asynchronously that is failing. Like this: CompletableFuture.runAsync( () -> { throw new RuntimeException("bad"); }, executorService ); We want default exception handling code that can catch these errors, in case specific uses forget to handle exceptions (this came from a production bug). This is apparently tricky. The answer given in Handling exceptions from Java ExecutorService tasks does not work. It relies on the task being a Future<?> and then

问题 I have a set of Futures created by submitting Callable s to an Executor . Pseudo code: for all tasks futures.add(executor.submit(new callable(task))) Now I'd like to get all futures waiting at most n seconds until all complete. I know I can call Future#get(timeout) but if I call that sequentially for all my futures in a loop the timouts start adding up. Pseudo code: for all futures future.get(timeout) get blocks with a timeout until the result is ready. Therefore, if the first completes just

问题 I have a set of Futures created by submitting Callable s to an Executor . Pseudo code: for all tasks futures.add(executor.submit(new callable(task))) Now I'd like to get all futures waiting at most n seconds until all complete. I know I can call Future#get(timeout) but if I call that sequentially for all my futures in a loop the timouts start adding up. Pseudo code: for all futures future.get(timeout) get blocks with a timeout until the result is ready. Therefore, if the first completes just

问题 I consider that main thread must end after sub thread.But below code shows the process finished before print the "async end".What is the reason?Can anybody explain?Thx. import java.util.concurrent.CompletableFuture; public class Test { public static void main(String[] args) { CompletableFuture.runAsync(() -> { try { System.out.println("async start"); Thread.sleep(3000); System.out.println("async end"); } catch (InterruptedException e) { e.printStackTrace(); } }); System.out.println("main end"

问题 I consider that main thread must end after sub thread.But below code shows the process finished before print the "async end".What is the reason?Can anybody explain?Thx. import java.util.concurrent.CompletableFuture; public class Test { public static void main(String[] args) { CompletableFuture.runAsync(() -> { try { System.out.println("async start"); Thread.sleep(3000); System.out.println("async end"); } catch (InterruptedException e) { e.printStackTrace(); } }); System.out.println("main end"

问题 I consider that main thread must end after sub thread.But below code shows the process finished before print the "async end".What is the reason?Can anybody explain?Thx. import java.util.concurrent.CompletableFuture; public class Test { public static void main(String[] args) { CompletableFuture.runAsync(() -> { try { System.out.println("async start"); Thread.sleep(3000); System.out.println("async end"); } catch (InterruptedException e) { e.printStackTrace(); } }); System.out.println("main end"