CODEWITHSUNDEEP
javaasynchronousconcurrencynonblockingcompletable-future
Fizi
Fizi

Reputation: 1861

CompletableFuture - supply a method that returns bool value to supplyAsync call

I am getting back into Java after a long long time so apologies if the question seems stupid. I am trying to use CompletableFuture to create a non-blocking call. I have a method that returns a boolean

public boolean waitOnState(final String targetState, final long waitMs) {
        long begin = System.nanoTime()/1000000;
        synchronized (stateLock) {
            long elapsedMs = 0L;
            logger.debug(this.storeName + "-" + this.getStreamState().toString());
            while (!this.getStreamState().toString().equals(targetState)) {

                if (waitMs > elapsedMs) {
                    long remainingMs = waitMs - elapsedMs;
                    try {
                        logger.debug("Waiting on stream to be in run state in "+remainingMs);
                        stateLock.wait(remainingMs);
                    } catch (final InterruptedException e) {
                        // it is ok: just move on to the next iteration
                    }
                } else {
                    logger.debug("Cannot transit to target state");
                    return false;
                }
                elapsedMs = System.nanoTime()/1000000 - begin;
            }
            logger.debug("State is running - "+this.storeName);
            return true;
        }
    }

And i pass this function to completedFuture in this way:

CompletableFuture<Boolean> resultHandle = 
                CompletableFuture.supplyAsync(this.waitOnState("RUNNING", 100000));
        resultHandle.thenAccept(result -> System.out.println(result));

But I get an error The method supplyAsync(Supplier<U>) in the type *CompletableFuture* is not applicable for the arguments (boolean)

The error persists even if I change the return type of my function to Boolean or Integer so I am sure I am invoking the CompletableFuture incorrectly

Upvotes: 2

Views: 4686

Answers (1)

ernest_k
ernest_k

Reputation: 45319

You should rather give it a supplier, so don't invoke the method inline, rather make it a lambda expression:

CompletableFuture<Boolean> resultHandle = 
            CompletableFuture.supplyAsync(() -> 
                 this.waitOnState("RUNNING", 100000));

() -> this.waitOnState("RUNNING", 100000) is a lambda expression that the compiler can make a Supplier from, but this.waitOnState("RUNNING", 100000) is a boolean expression.

Upvotes: 2

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