Is there a way to calculate the time required to complete every completableFuture?

Question

Before I jump into the specifics of the question, I want to give the context of the problem. Basically, my code looks like

for(int i = 0; i < n; i++){
    startTime = System.currentTimeMillis();
    result = doSomething();
    endTime = System.currentTimeMillis();
    responseTime.add(endTime - startTime);
    results.add(result);
} 
print(results and responseTime);

Now what i want to do is run doSomething() as a completableFuture and get the responseTime as mentioned above. But since doing something like this would be totally incorrect --

for(int i = 0; i < n; i++){
    startTime = System.currentTimeMillis();
    resultCF = CompletableFuture.supplyasync(() -> doSomething());
    endTime = System.currentTimeMillis();
    responseTime.add(endTime - startTime);
    results.add(resultCF); //result is to store the completableFutures
}
CompletableFuture.allOf(results.toArray(new CompletableFuture[results.size()])).join();
print(i.get() for i in results and responseTimes);

since it would defeat the purpose of getting the execution time of each doSomething(). So, is there any way I can get the response time of each completableFuture? Also, i would need the results arraylist containing the completableFutures(resultCF) at the end of the loop.

Answer 1

The easiest may be to just add a stage to resultCF, which itself adds the response time to the list. resultCF will be completed after this part is done:

resultCF = CompletableFuture.supplyasync(() -> doSomething())
              .thenApply(s -> {
                  responseTime.add(System.currentTimeMillis() - startTime);
                  return s;
               });
results.add(resultCF);