JobEngine.cs

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 * See CONTRIBUTORS.TXT for a full list of copyright holders.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
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 *       notice, this list of conditions and the following disclaimer.
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 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
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 * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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using System;
using System.Collections.Concurrent;
using System.Reflection;
using System.Threading;
using log4net;
using OpenSim.Framework;

namespace OpenSim.Framework.Monitoring
{
    public class JobEngine
    {
        private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        public int LogLevel { get; set; }

        private object JobLock = new object();

        public string Name { get; private set; }

        public string LoggingName { get; private set; }

        public bool IsRunning { get; private set; } 

        public Job CurrentJob { get; private set; }

        public int JobsWaiting { get { return m_jobQueue.Count; } }

        public int RequestProcessTimeoutOnStop { get; set; }

        private bool m_warnOverMaxQueue = true;

        private BlockingCollection<Job> m_jobQueue = new BlockingCollection<Job>(new ConcurrentQueue<Job>(), 5000);

        private CancellationTokenSource m_cancelSource;

        private ManualResetEvent m_finishedProcessingAfterStop = new ManualResetEvent(false);

        public JobEngine(string name, string loggingName)
        {
            Name = name;
            LoggingName = loggingName;

            RequestProcessTimeoutOnStop = 5000;
        }

        public void Start()
        {
            lock (JobLock)
            {
                if (IsRunning)
                    return;

                IsRunning = true;

                m_finishedProcessingAfterStop.Reset();

                m_cancelSource = new CancellationTokenSource();

                WorkManager.StartThread(
                    ProcessRequests,
                    Name,
                    ThreadPriority.Normal,
                    false,
                    true,
                    null,
                    int.MaxValue);
            }
        }

        public void Stop()
        {   
            lock (JobLock)
            {
                try
                {
                    if (!IsRunning)
                        return;

                    m_log.DebugFormat("[JobEngine] Stopping {0}", Name);

                    IsRunning = false;

                    m_finishedProcessingAfterStop.Reset();
                    if(m_jobQueue.Count <= 0)
                        m_cancelSource.Cancel();

                    m_finishedProcessingAfterStop.WaitOne(RequestProcessTimeoutOnStop);
                }
                finally
                {
                    m_cancelSource.Dispose();
                }
            }
        }

        public static Job MakeJob(string name, Action action, string commonId = null)
        {
            return Job.MakeJob(name, action, commonId);
        }

        public Job RemoveNextJob()
        {
            Job nextJob;
            m_jobQueue.TryTake(out nextJob);

            return nextJob;
        }

        public bool QueueJob(string name, Action action, string commonId = null)
        {
            return QueueJob(MakeJob(name, action, commonId));
        }

        public bool QueueJob(Job job)
        {
            if (m_jobQueue.Count < m_jobQueue.BoundedCapacity)
            {
                m_jobQueue.Add(job);

                if (!m_warnOverMaxQueue)
                    m_warnOverMaxQueue = true;

                return true;
            }
            else
            {
                if (m_warnOverMaxQueue)
                {
                    m_log.WarnFormat(
                        "[{0}]: Job queue at maximum capacity, not recording job from {1} in {2}",
                        LoggingName, job.Name, Name);

                    m_warnOverMaxQueue = false;
                }

                return false;
            }
        }

        private void ProcessRequests()
        {
            while(IsRunning || m_jobQueue.Count > 0)
            {
                try
                {
                    CurrentJob = m_jobQueue.Take(m_cancelSource.Token);
                }
                catch(ObjectDisposedException e)
                {
                    // If we see this whilst not running then it may be due to a race where this thread checks
                    // IsRunning after the stopping thread sets it to false and disposes of the cancellation source.
                    if(IsRunning)
                        throw e;
                    else
                    {
                        m_log.DebugFormat("[JobEngine] {0} stopping ignoring {1} jobs in queue",
                                Name,m_jobQueue.Count);
                        break;
                    }
                }
                catch(OperationCanceledException)
                {
                    break;
                }

                if(LogLevel >= 1)
                    m_log.DebugFormat("[{0}]: Processing job {1}",LoggingName,CurrentJob.Name);

                try
                {
                    CurrentJob.Action();
                }
                catch(Exception e)
                {
                    m_log.Error(
                        string.Format(
                        "[{0}]: Job {1} failed, continuing.  Exception  ",LoggingName,CurrentJob.Name),e);
                }

                if(LogLevel >= 1)
                    m_log.DebugFormat("[{0}]: Processed job {1}",LoggingName,CurrentJob.Name);

                CurrentJob = null;
            }

            Watchdog.RemoveThread(false);
            m_finishedProcessingAfterStop.Set();
        }

        public class Job
        {
            public string Name { get; private set; }

            public string CommonId { get; private set; }

            public Action Action { get; private set; }

            private Job(string name, string commonId, Action action)
            {
                Name = name;
                CommonId = commonId;
                Action = action;
            }
                        
            public static Job MakeJob(string name, Action action, string commonId = null)
            {
                return new Job(name, commonId, action);
            }
        }
    }
}