Java Executor with throttling/throughput control

Question

I'm looking for a Java Executor that allows me to specify throttling/throughput/pacing limitations, for example, no more than say 100 tasks can be processed in a second -- if more tasks get submitted they should get queued and executed later. The main purpose of this is to avoid running into limits when hitting foreign APIs or servers.

I'm wondering whether either base Java (which I doubt, because I checked) or somewhere else reliable (e.g. Apache Commons) provides this, or if I have to write my own. Preferably something lightweight. I don't mind writing it myself, but if there's a "standard" version out there somewhere I'd at least like to look at it first.

Answer 1

Take a look at guavas RateLimiter:

A rate limiter. Conceptually, a rate limiter distributes permits at a configurable rate. Each acquire() blocks if necessary until a permit is available, and then takes it. Once acquired, permits need not be released. Rate limiters are often used to restrict the rate at which some physical or logical resource is accessed. This is in contrast to Semaphore which restricts the number of concurrent accesses instead of the rate (note though that concurrency and rate are closely related, e.g. see Little's Law).

Its threadsafe, but still @Beta. Might be worth a try anyway.

You would have to wrap each call to the Executor with respect to the rate limiter. For a more clean solution you could create some kind of wrapper for the ExecutorService.

From the javadoc:

 final RateLimiter rateLimiter = RateLimiter.create(2.0); // rate is "2 permits per second"   void submitTasks(List<Runnable> tasks, Executor executor) {     for (Runnable task : tasks) {       rateLimiter.acquire(); // may wait       executor.execute(task);     }   } 

Answer 2

The Java Executor doesn't offer such a limitation, only limitation by amount of threads, which is not what you are looking for.

In general the Executor is the wrong place to limit such actions anyway, it should be at the moment where the Thread tries to call the outside server. You can do this for example by having a limiting Semaphore that threads wait on before they submit their requests.

Calling Thread:

public void run() {
  // ...
  requestLimiter.acquire();
  connection.send();
  // ...
 }

While at the same time you schedule a (single) secondary thread to periodically (like every 60 seconds) releases acquired resources:

 public void run() {
  // ...
  requestLimiter.drainPermits();  // make sure not more than max are released by draining the Semaphore empty
  requestLimiter.release(MAX_NUM_REQUESTS);
  // ...
 }