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The AWS SDK for Java with support for OSGi. The AWS SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2015-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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.
 */
package com.amazonaws.http.timers.client;

import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import com.amazonaws.annotation.SdkInternalApi;
import com.amazonaws.annotation.SdkTestInternalApi;
import com.amazonaws.annotation.ThreadSafe;
import com.amazonaws.http.AmazonHttpClient;
import com.amazonaws.http.timers.TimeoutThreadPoolBuilder;

/**
 * Represents a timer to enforce a timeout on the total client execution time. That is the time
 * spent executing request handlers, any HTTP request including retries, unmarshalling, etc.
 * Essentially all the time spent in {@link AmazonHttpClient}
 */
@SdkInternalApi
@ThreadSafe
public class ClientExecutionTimer {

    private volatile ScheduledThreadPoolExecutor executor;

    /**
     * Start the timer with the specified timeout and return a object that can be used to track the
     * state of the timer and cancel it if need be.
     * 
     * @param clientExecutionTimeoutMillis
     *            A positive value here enables the timer, a non-positive value disables it and
     *            returns a dummy tracker task
     * @return Implementation of {@link ClientExecutionAbortTrackerTaskImpl} to query the state of
     *         the task, provide it with up to date context, and cancel it if appropriate
     */
    public ClientExecutionAbortTrackerTask startTimer(int clientExecutionTimeoutMillis) {
        if (isTimeoutDisabled(clientExecutionTimeoutMillis)) {
            return NoOpClientExecutionAbortTrackerTask.INSTANCE;
        } else if (executor == null) {
            initializeExecutor();
        }
        return scheduleTimerTask(clientExecutionTimeoutMillis);
    }

    /**
     * Executor is lazily initialized as it's not compatible with Java 6
     */
    private synchronized void initializeExecutor() {
        if (executor == null) {
            executor = TimeoutThreadPoolBuilder.buildDefaultTimeoutThreadPool();
        }
    }

    /**
     * This method is current exposed for testing purposes
     * 
     * @return The underlying {@link ScheduledThreadPoolExecutor}
     */
    @SdkTestInternalApi
    public ScheduledThreadPoolExecutor getExecutor() {
        return this.executor;
    }

    /**
     * Shutdown the underlying {@link ScheduledThreadPoolExecutor}. Should be invoked when
     * {@link AmazonHttpClient} is shutdown
     */
    public synchronized void shutdown() {
        if (executor != null) {
            executor.shutdown();
        }
    }

    private ClientExecutionAbortTrackerTask scheduleTimerTask(int clientExecutionTimeoutMillis) {
        ClientExecutionAbortTask timerTask = new ClientExecutionAbortTaskImpl(Thread.currentThread());
        ScheduledFuture timerTaskFuture = executor.schedule(timerTask, clientExecutionTimeoutMillis,
                TimeUnit.MILLISECONDS);
        return new ClientExecutionAbortTrackerTaskImpl(timerTask, timerTaskFuture);
    }

    private boolean isTimeoutDisabled(int clientExecutionTimeoutMillis) {
        return clientExecutionTimeoutMillis <= 0;
    }

}