xenadmin/XenCenterLib/QueuedBackgroundWorker.cs

/* Copyright (c) Citrix Systems Inc. 
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 * Redistribution and use in source and binary forms, 
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 *     following disclaimer. 
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 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
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using System.Collections.Generic;
using System.ComponentModel;

namespace XenCenterLib
{
    /// <summary>
    /// This is thread-safe
    /// </summary>
    public class QueuedBackgroundWorker:BackgroundWorker
    {
        private Queue<BackgroundWorker> Queue = new Queue<BackgroundWorker>();

        private object _lock = new object();

        public delegate object DoWorkQueuedEventHandler(object sender, object argument);

        public void RunWorkerAsync(DoWorkQueuedEventHandler doWork, RunWorkerCompletedEventHandler workerCompleted)
        {
            BackgroundWorker bw = GetBackgroundWorker(doWork, workerCompleted);

            Queue.Enqueue(bw);

            lock (_lock)
            {
                if (Queue.Count == 1)
                {
                    ((BackgroundWorker)this.Queue.Peek()).RunWorkerAsync();
                }
            }
        }

        private BackgroundWorker GetBackgroundWorker(DoWorkQueuedEventHandler doWork, RunWorkerCompletedEventHandler workerCompleted)
        {
            BackgroundWorker bw = new BackgroundWorker();
            bw.WorkerReportsProgress = false;
            bw.WorkerSupportsCancellation = false;

            bw.DoWork += (sender, args) =>
                             {
                                 if (doWork != null)
                                 {
                                     args.Result=doWork(this, new DoWorkEventArgs(args.Argument));
                                 }
                             };

            bw.RunWorkerCompleted += (sender, args) =>
                                         {
                                             if (workerCompleted != null)
                                             {
                                                 object result = args.Error == null ? args.Result : null;
                                                 workerCompleted(this,
                                                                 new RunWorkerCompletedEventArgs(result, args.Error,
                                                                                                 args.Cancelled));
                                             }
                                             Queue.Dequeue();
                                             lock (_lock)
                                             {
                                                 if (Queue.Count > 0)
                                                 {
                                                     ((BackgroundWorker)this.Queue.Peek()).RunWorkerAsync();
                                                 }
                                             }
                                         };
            return bw;
        }


    
    }
}