001/*
002 * Copyright 2014 Alex Kasko (alexkasko.com)
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.alexkasko.unsafe.offheapstruct;
018
019import java.util.Collection;
020import java.util.Iterator;
021import java.util.concurrent.*;
022
023/**
024 * Auxiliary class that limits the number of {@link java.util.concurrent.Executor} threads
025 * those can be used simultaneously.
026 *
027 * @author alexkasko
028 * Date: 11/14/13
029 */
030class LimitedInvoker {
031    private final Executor executor;
032    private final int maxThreads;
033
034    /**
035     * Constructor
036     *
037     * @param executor executor
038     * @param maxThreads maximum number of simultaneously used threads
039     */
040    LimitedInvoker(Executor executor, int maxThreads) {
041        if (null == executor) throw new NullPointerException("executor");
042        if (maxThreads <= 0) throw new IllegalArgumentException("maxThreads: [" + maxThreads + "] must be positive");
043        this.executor = executor;
044        this.maxThreads = maxThreads;
045    }
046
047    /**
048     * Executes all the tasks simultaneously using no more than {@link #maxThreads} threads from the executor
049     *
050     * @param tasks runnables to execute
051     */
052    void invokeAll(Collection<? extends Runnable> tasks) {
053        ExecutorCompletionService<Void> completer = new ExecutorCompletionService<Void>(executor);
054        Iterator<? extends Runnable> iter = tasks.iterator();
055        int realMaxThreads = Math.min(maxThreads, tasks.size());
056        for (int i = 0; i < realMaxThreads; i++) {
057            completer.submit(iter.next(), null);
058        }
059        for (int i = realMaxThreads; i > 0; ) {
060            await(completer);
061            i -= 1;
062            if (iter.hasNext()) {
063                completer.submit(iter.next(), null);
064                i += 1;
065            }
066        }
067    }
068
069    /**
070     * Waits for {@link java.util.concurrent.Future} to complete
071     *
072     * @param completer executor service
073     */
074    private void await(ExecutorCompletionService<Void> completer) {
075        try {
076            Future<Void> fu = completer.take();
077            fu.get();
078        } catch (InterruptedException e) {
079            throw new RuntimeException(e);
080        } catch (ExecutionException e) {
081            throw new RuntimeException(e);
082        }
083    }
084}