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Common utility code (Apache License v2) 2008-2024 Matt Gumbley, DevZendo.org
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package org.devzendo.commoncode.timeout;

import org.devzendo.commoncode.concurrency.DaemonThreadFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;

/**
 * Copyright (C) 2008-2016 Matt Gumbley, DevZendo.org http://devzendo.org
 * 
 * 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 permissions and
 * limitations under the License.
 */
public class DefaultTimeoutScheduler implements TimeoutScheduler {
    private static final Logger logger = LoggerFactory.getLogger(DefaultTimeoutScheduler.class);

    private final AtomicInteger usageCount = new AtomicInteger(0);
    private final Map> activeTimeouts = new ConcurrentHashMap<>();
    private final AtomicLong timeoutIdCount = new AtomicLong(0);
    private final ScheduledThreadPoolExecutor executor;

    public DefaultTimeoutScheduler() {
        executor = new ScheduledThreadPoolExecutor(10, new DaemonThreadFactory("timeout-scheduler-thread-"));
        executor.setRemoveOnCancelPolicy(true);
        executor.setExecuteExistingDelayedTasksAfterShutdownPolicy(false);
    }

    @Override
    public TimeoutId schedule(final long millisecondsFromNow, final Runnable runnable) {
        if (usageCount.get() == 0) {
            throw new IllegalStateException("Cannot schedule when scheduler is stopped");
        }

        final long thisTimeoutId = timeoutIdCount.incrementAndGet();
        final TimeoutId timeoutId = new TimeoutId(thisTimeoutId);
        final Runnable exceptionLoggingRunnable = () -> {
            try {
                runnable.run();
            } catch (final Exception e) {
                logger.warn("Timeout handler threw " + e.getClass().getSimpleName() + ": " + e.getMessage(), e);
            }
        };
        final ScheduledFuture schedule = executor.schedule(exceptionLoggingRunnable, millisecondsFromNow, TimeUnit.MILLISECONDS);
        activeTimeouts.put(timeoutId, schedule);
        return timeoutId;
    }

    @Override
    public boolean cancel(final TimeoutId timeoutId) {
        if (usageCount.get() == 0) {
            throw new IllegalStateException("Cannot cancel when scheduler is stopped");
        }

        final ScheduledFuture schedule = activeTimeouts.remove(timeoutId);
        return schedule != null && schedule.cancel(false);
    }

    @Override
    public void start() {
        usageCount.incrementAndGet();
    }

    @Override
    public boolean isStarted() {
        return usageCount.get() > 0;
    }

    @Override
    public synchronized void stop() {
        if (usageCount.get() == 0) {
            throw new IllegalStateException("Cannot stop scheduler if it has not been started");
        }

        final int count = usageCount.decrementAndGet();
        if (count == 0) {
            executor.shutdown();
        }
    }
}