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BoundedScheduledThreadPoolExecutor.java
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/*
* Copyright 2019-2020 Volkan Yazıcı
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permits and
* limitations under the License.
*/
package com.vlkan.pubsub.util;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.*;
/**
* A {@link ScheduledThreadPoolExecutor} wrapper enforcing a bound on the task
* queue size. Excessive task queue growth yields {@link
* RejectedExecutionException} errors. {@link RejectedExecutionHandler}s are
* not supported since they expect a {@link ThreadPoolExecutor} in their
* arguments.
*
* <p>Java Standard library unfortunately doesn't provide any {@link
* ScheduledExecutorService} implementations that one can provide a bound on
* the task queue. This shortcoming is prone to hide backpressure problems. See
* <a href="http://cs.oswego.edu/pipermail/concurrency-interest/2019-April/016861.html">the
* relevant concurrency-interest discussion</a> for {@link java.util.concurrent}
* lead Doug Lea's tip for enforcing a bound via {@link
* ScheduledThreadPoolExecutor#getQueue()}.
*/
@SuppressWarnings("NullableProblems")
public class BoundedScheduledThreadPoolExecutor implements ScheduledExecutorService {
private final int queueCapacity;
private final ScheduledThreadPoolExecutor executor;
public BoundedScheduledThreadPoolExecutor(
int queueCapacity,
ScheduledThreadPoolExecutor executor) {
if (queueCapacity < 1) {
throw new IllegalArgumentException(
"was expecting a non-zero positive queue capacity");
}
this.queueCapacity = queueCapacity;
this.executor = executor;
}
/**
* {@inheritDoc}
*/
@Override
public synchronized ScheduledFuture<?> schedule(
Runnable command,
long delay,
TimeUnit unit) {
ensureQueueCapacity(1);
return executor.schedule(command, delay, unit);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized <V> ScheduledFuture<V> schedule(
Callable<V> callable,
long delay,
TimeUnit unit) {
ensureQueueCapacity(1);
return executor.schedule(callable, delay, unit);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized ScheduledFuture<?> scheduleAtFixedRate(
Runnable command,
long initialDelay,
long period,
TimeUnit unit) {
ensureQueueCapacity(1);
return executor.scheduleAtFixedRate(command, initialDelay, period, unit);
}
/**
* {@inheritDoc}
*/
@Override
public ScheduledFuture<?> scheduleWithFixedDelay(
Runnable command,
long initialDelay,
long delay,
TimeUnit unit) {
ensureQueueCapacity(1);
return executor.scheduleWithFixedDelay(command, initialDelay, delay, unit);
}
/**
* {@inheritDoc}
*/
@Override
public void shutdown() {
executor.shutdown();
}
/**
* {@inheritDoc}
*/
@Override
public List<Runnable> shutdownNow() {
return executor.shutdownNow();
}
/**
* {@inheritDoc}
*/
@Override
public boolean isShutdown() {
return executor.isShutdown();
}
/**
* {@inheritDoc}
*/
@Override
public boolean isTerminated() {
return executor.isTerminated();
}
/**
* {@inheritDoc}
*/
@Override
public boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException {
return executor.awaitTermination(timeout, unit);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized <T> Future<T> submit(Callable<T> task) {
ensureQueueCapacity(1);
return executor.submit(task);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized <T> Future<T> submit(Runnable task, T result) {
ensureQueueCapacity(1);
return executor.submit(task, result);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized Future<?> submit(Runnable task) {
ensureQueueCapacity(1);
return executor.submit(task);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized <T> List<Future<T>> invokeAll(
Collection<? extends Callable<T>> tasks)
throws InterruptedException {
ensureQueueCapacity(tasks.size());
return executor.invokeAll(tasks);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized <T> List<Future<T>> invokeAll(
Collection<? extends Callable<T>> tasks,
long timeout,
TimeUnit unit)
throws InterruptedException {
ensureQueueCapacity(tasks.size());
return executor.invokeAll(tasks, timeout, unit);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized <T> T invokeAny(Collection<? extends Callable<T>> tasks)
throws InterruptedException, ExecutionException {
ensureQueueCapacity(tasks.size());
return executor.invokeAny(tasks);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized <T> T invokeAny(
Collection<? extends Callable<T>> tasks,
long timeout,
TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
ensureQueueCapacity(tasks.size());
return executor.invokeAny(tasks, timeout, unit);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized void execute(Runnable command) {
ensureQueueCapacity(1);
executor.submit(command);
}
private void ensureQueueCapacity(int taskCount) {
int queueSize = executor.getQueue().size();
if ((queueSize + taskCount) >= queueCapacity) {
throw new RejectedExecutionException();
}
}
}