CODEWITHSUNDEEP
javaconcurrencyexecutorservice
CBSCA
CBSCA

Reputation: 1

How to get ExecutorService or CompletionService to finish without asking for values of Futures?

We have some work to be done within a thread which will be run on a server for a web app using Spring Boot .

What we want to happen is: 1) Work is submitted as our custom Runnable object 2) Work completes when it gets its turn (it's a database operation, and we don't need any return value except perhaps returning "Success" if the run() completed without exceptions)

However, in our JUnit tests, it seems all the tasks submitted to an ExecutorService or CompletionService disappear when the main thread is finished, unless we call take() every time we add a new task (since it blocks until a task is finished, this makes tasks run sequentially, which defeats the purpose) or if we maintain a list of futures and call a method to loop through the list and get() the value of each feature.

The latter option we don't think is ideal because as a server application, we will have requests constantly coming in from different users and don't know how to detect when we should be clearing out the list of futures.

Why do the threads silently disappear and what is a way around this?

Upvotes: 0

Views: 770

Answers (1)

Bohemian
Bohemian

Reputation: 425003

Don't run the code async: Just test the Runnable directly:

@Test
public void test() {
    Runnable r = <your runnable>;
    r.run();
    // various assertions
}

It's pointless testing that your chosen ExecutorService does its job - you can assume that.

If you want to assert that your application is behaving correctly, use functional tests; ie, spin up a container (eg using @SpringJUnit4ClassRunner) with a hypersonic datasource, hit the spring boot end point then make you assertions about effect on the database.

If you use spring boot's @Async annotation for your service, you can even provide a configuration that uses a SynchronousTaskExecutor so you don't have to pause in your test before making assertions.

Upvotes: 1

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