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Throttle the number of concurrent tasks in a thread pool.
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import java.util.LinkedList; | |
import java.util.Random; | |
import java.util.concurrent.CompletableFuture; | |
import java.util.concurrent.Executor; | |
import java.util.concurrent.ExecutorService; | |
import java.util.concurrent.Executors; | |
import java.util.function.BiConsumer; | |
import java.util.function.Supplier; | |
public class ThrottlingInvoker{ | |
private Executor executor; | |
private int limit; | |
private int concurrent; | |
private LinkedList<Task> queue = new LinkedList<>(); | |
public ThrottlingInvoker(Executor executor, int limit) { | |
this.executor = executor; | |
this.limit = limit; | |
} | |
synchronized | |
public <T> CompletableFuture<T> invoke(Supplier<T> supplier) { | |
CompletableFuture future = new CompletableFuture(); | |
if (concurrent < limit) { | |
acquire(new Task(supplier, future)); | |
} else { | |
queue.addFirst(new Task(supplier, future)); | |
} | |
return future; | |
} | |
synchronized | |
private void acquire(Task task) { | |
concurrent++; | |
CompletableFuture wrappedFuture = CompletableFuture.supplyAsync(task.supplier, executor); | |
BiConsumer<Object, Exception> onComplete = (result, exception) -> { | |
if (exception != null) { | |
task.future.completeExceptionally(exception); | |
} else { | |
task.future.complete(result); | |
} | |
release(); | |
}; | |
wrappedFuture.whenComplete(onComplete); | |
} | |
synchronized | |
private void release() { | |
concurrent --; | |
Task task = queue.removeLast(); | |
if (task != null) { | |
acquire(task); | |
} | |
} | |
public int getConcurrent() { | |
return concurrent; | |
} | |
class Task { | |
private final Supplier supplier; | |
private final CompletableFuture future; | |
Task(Supplier supplier, CompletableFuture future) { | |
this.supplier = supplier; | |
this.future = future; | |
} | |
} | |
public static void main(String[] args) { | |
ExecutorService executorService = Executors.newCachedThreadPool(); | |
ThrottlingInvoker invoker = new ThrottlingInvoker(executorService, 20); | |
Random rand = new Random(); | |
for (int i=0; i<200; i++) { | |
final int fi = i; | |
invoker.invoke(() -> { | |
System.out.println("invoked:" + fi); | |
try { | |
Thread.sleep(rand.nextInt(1000)); | |
} catch (InterruptedException e) { | |
e.printStackTrace(); | |
} | |
return "task " + fi; | |
}).whenComplete((name, throwable)-> { | |
System.out.println("complete: " + name + " concurrent:" + invoker.getConcurrent()); | |
}); | |
} | |
} | |
} |
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