QueueProcessor.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / UIAutomation / UIAutomationClient / MS / Internal / Automation / QueueProcessor.cs / 1305600 / QueueProcessor.cs
                        
                        
                            //---------------------------------------------------------------------------- 
//
// 
//    Copyright (C) Microsoft Corporation.  All rights reserved.
//  
//
// 
// Description: Class to create a queue on its own thread. 
//
// History: 
//  06/17/2003 : BrendanM Ported to WCP
//
//---------------------------------------------------------------------------
 
// PRESHARP: In order to avoid generating warnings about unkown message numbers and unknown pragmas.
#pragma warning disable 1634, 1691 
 
using System.Windows.Automation;
using System.Windows.Automation.Provider; 
using System;
using System.Threading;
using System.Collections;
using System.Diagnostics; 
using MS.Internal.Automation;
using MS.Win32; 
using System.Runtime.InteropServices; 
using Microsoft.Win32.SafeHandles;
 
namespace MS.Internal.Automation
{

    // Abstract class for worker objects queued to the QueueProcessor class 
    internal abstract class QueueItem
    { 
        internal abstract void Process(); 
    }
 

    // Class to create a queue on its own thread.  Used  on the PAW client-side
    // to queue client callbacks.  This prevents a deadlock situation when the
    // client calls back into PAW from w/in a callback.  All events are queued 
    // through this class.
    internal class QueueProcessor 
    { 
        //-----------------------------------------------------
        // 
        //  Constructors
        //
        //-----------------------------------------------------
 
        #region Constructors
 
        // Usage is create QueueProcessor object and call StartOnThread 
        internal QueueProcessor(int initCapacity)
        { 
            _ev = new AutoResetEvent(false);
            _q = Queue.Synchronized(new Queue(initCapacity));
        }
 
        internal QueueProcessor()
            : this(4) 
        { 
        }
 
        #endregion Constructors


        //------------------------------------------------------ 
        //
        //  Internal Methods 
        // 
        //-----------------------------------------------------
 
        #region Internal Methods

        internal void StartOnThread()
        { 
            _quitting = false;
 
            // create and start a background thread for this worker window to run on 
            // (background threads will exit if the main and foreground threads exit)
            ThreadStart threadStart = new ThreadStart(WaitForWork); 
            _thread = new Thread(threadStart);
            _thread.IsBackground = true;
            _thread.Start();
        } 

        // Post a work item to the queue (from another thread) 
        internal bool PostWorkItem(QueueItem workItem) 
        {
            Debug.Assert(!_quitting, "Can't add items to queue when quitting"); 
            _q.Enqueue(workItem);
            _ev.Set();
            return true;
        } 

        // Post a work item and wait for it to be processed 
        // Return true if the item was processed w/in 2 sec else false 
        internal bool PostSyncWorkItem(QueueItem workItem)
        { 
            Debug.Assert(!_quitting, "Can't add items to queue when quitting");
            SyncQueueItem syncItem = new SyncQueueItem(workItem);
            _q.Enqueue(syncItem);
            _ev.Set(); 
            return syncItem._ev.WaitOne(2000, false);
        } 
 
        // Stop queuing and clean up (from another thread)
        internal void PostQuit() 
        {
            _quitting = true;
            _ev.Set();
       } 

        #endregion Internal Methods 
 

        //------------------------------------------------------ 
        //
        //  Private Methods
        //
        //------------------------------------------------------ 

        #region Private Methods 
 
        // The loop the thread uses to wait for queue items to process
        private void WaitForWork() 
        {
            SafeWaitHandle handle = _ev.SafeWaitHandle;
            UnsafeNativeMethods.MSG msg = new UnsafeNativeMethods.MSG();
            while (!_quitting) 
            {
                // pump any messages 
                while (UnsafeNativeMethods.PeekMessage(ref msg, NativeMethods.HWND.NULL, 0, 0, UnsafeNativeMethods.PM_REMOVE)) 
                {
                    if (msg.message == UnsafeNativeMethods.WM_QUIT) 
                    {
                        break;
                    }
                    // From the Windows SDK documentation: 
                    // The return value specifies the value returned by the window procedure.
                    // Although its meaning depends on the message being dispatched, the return 
                    // value generally is ignored. 
#pragma warning suppress 6031, 6523
                    UnsafeNativeMethods.DispatchMessage(ref msg); 
                }

                // do any work items in the queue
                DrainQueue(); 

                int lastWin32Error = 0; 
                int result = Misc.TryMsgWaitForMultipleObjects(handle, false, UnsafeNativeMethods.INFINITE, UnsafeNativeMethods.QS_ALLINPUT, ref lastWin32Error); 
                if (result == UnsafeNativeMethods.WAIT_FAILED || result == UnsafeNativeMethods.WAIT_TIMEOUT)
                { 
                    DrainQueue();
                    Debug.Assert(_quitting, "MsgWaitForMultipleObjects failed while WaitForWork");
                    break;
                } 
            }
            DrainQueue(); 
        } 

        private void DrainQueue() 
        {
            // It's possible items could be enqueued between when we check for the count
            // and dequeue but the event is set then and we'll come back into DrainQueue.
            // (note: don't use a for loop here because as the counter is incremented 
            // Count is decremented and we'll only process half the queue)
            while (_q.Count > 0) 
            { 
                // pull an item off the queue, process, then clear it
                QueueItem item = (QueueItem)_q.Dequeue(); 
                if (! _quitting)
                {
                    try
                    { 
                        item.Process();
                    } 
                    catch (Exception e) 
                    {
                        if (Misc.IsCriticalException(e)) 
                            throw;
                        // Eat it.
                        // There's no place to let this exception percolate out
                        // to so we'll stop it here. 
                    }
                } 
            } 
        }
 
        #endregion Private Methods


        //----------------------------------------------------- 
        //
        //  Private Fields 
        // 
        //------------------------------------------------------
 
        #region Private Fields

        Thread _thread;              // the thread on which QueueItem's are processed
        private Queue _q;            // a synchronized queue 
        private AutoResetEvent _ev;  // notifies when new queue items show up
        private bool _quitting;      // true if need to stop queueing 
 
        #endregion Private Fields
    } 


    // Class is used only by QueueProcessor class itself - wraps
    // another QueueItem, and fires an event when it is complete. 
    internal class SyncQueueItem : QueueItem
    { 
        //----------------------------------------------------- 
        //
        //  Constructors 
        //
        //-----------------------------------------------------

        #region Constructors 

        internal SyncQueueItem(QueueItem qItem) 
        { 
            _ev = new AutoResetEvent(false);
            _qItem = qItem; 
        }

        #endregion Constructors
 

        //----------------------------------------------------- 
        // 
        //  Internal Methods
        // 
        //------------------------------------------------------

        #region Internal Methods
 
        internal override void Process()
        { 
            _qItem.Process(); 
            _ev.Set();
        } 

        #endregion Internal Methods

 
        //-----------------------------------------------------
        // 
        //  Private Fields 
        //
        //------------------------------------------------------ 

        #region Private Fields

        // Not many of these will be created at a time so having the 
        // event in the class is OK and easier than having just one
        // that manages any [....] method call. 
        internal AutoResetEvent _ev; 
        private QueueItem _qItem;
 
        #endregion Private Fields
    }
}

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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