SynchronizationContext.cs source code in C# .NET

                        Code:
                         / FXUpdate3074 / FXUpdate3074 / 1.1 / untmp / whidbey / QFE / ndp / clr / src / BCL / System / Threading / SynchronizationContext.cs / 2 / SynchronizationContext.cs
                        
                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
/*============================================================ 
**
** Class:  SynchronizationContext 
** 
**
** Purpose: Capture synchronization semantics for asynchronous callbacks 
**
**
===========================================================*/
 
namespace System.Threading
{ 
    using Microsoft.Win32.SafeHandles; 
    using System.Security.Permissions;
    using System.Runtime.InteropServices; 
    using System.Runtime.CompilerServices;
    using System.Runtime.ConstrainedExecution;
    using System.Reflection;
 

    internal struct SynchronizationContextSwitcher : IDisposable 
    { 
        internal SynchronizationContext savedSC;
        internal SynchronizationContext currSC; 
        internal ExecutionContext _ec;

        public override bool Equals(Object obj)
        { 
            if (obj == null || !(obj is SynchronizationContextSwitcher))
                return false; 
            SynchronizationContextSwitcher sw = (SynchronizationContextSwitcher)obj; 
            return (this.savedSC == sw.savedSC && this.currSC == sw.currSC && this._ec == sw._ec);
        } 

        public override int GetHashCode()
        {
            return ToString().GetHashCode(); 
        }
 
        public static bool operator ==(SynchronizationContextSwitcher c1, SynchronizationContextSwitcher c2) 
        {
            return c1.Equals(c2); 
        }

        public static bool operator !=(SynchronizationContextSwitcher c1, SynchronizationContextSwitcher c2)
        { 
            return !c1.Equals(c2);
        } 
 

 

        /// 
        void IDisposable.Dispose()
        { 
            Undo();
        } 
 
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal bool UndoNoThrow() 
        {
            if (_ec  == null)
            {
                return true; 
            }
 
            try 
            {
                Undo(); 
            }
            catch
            {
                return false; 
            }
            return true; 
        } 
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        public void Undo() 
        {
            if (_ec  == null)
            {
                return; 
            }
 
            ExecutionContext  executionContext = Thread.CurrentThread.GetExecutionContextNoCreate(); 
            if (_ec != executionContext)
            { 
                throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_SwitcherCtxMismatch"));
            }
            if (currSC != _ec.SynchronizationContext)
            { 
                throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_SwitcherCtxMismatch"));
            } 
            BCLDebug.Assert(executionContext != null, " ExecutionContext can't be null"); 
            // restore the Saved Sync context as current
            executionContext.SynchronizationContext = savedSC; 
            // can't reuse this anymore
            _ec = null;
        }
    } 

 
    public delegate void SendOrPostCallback(Object state); 

    [Flags] 
    enum SynchronizationContextProperties
    {
        None = 0,
        RequireWaitNotification = 0x1 
    };
 
    [SecurityPermissionAttribute(SecurityAction.InheritanceDemand, Flags =SecurityPermissionFlag.ControlPolicy|SecurityPermissionFlag.ControlEvidence)] 
    public class SynchronizationContext
    { 
        SynchronizationContextProperties _props = SynchronizationContextProperties.None;

        public SynchronizationContext()
        { 
        }
 
 
        // protected so that only the derived sync context class can enable these flags
        protected void SetWaitNotificationRequired() 
        {
            // Prepare the method so that it can be called in a reliable fashion when a wait is needed.
            // This will obviously only make the Wait reliable if the Wait method is itself reliable. The only thing
            // preparing the method here does is to ensure there is no failure point before the method execution begins. 

            RuntimeHelpers.PrepareDelegate(new WaitDelegate(this.Wait)); 
            _props |= SynchronizationContextProperties.RequireWaitNotification; 
        }
 
        public bool IsWaitNotificationRequired()
        {
            return ((_props & SynchronizationContextProperties.RequireWaitNotification) != 0);
        } 

 
 
        public virtual void Send(SendOrPostCallback d, Object state)
        { 
            d(state);
        }

        public virtual void Post(SendOrPostCallback d, Object state) 
        {
            ThreadPool.QueueUserWorkItem(new WaitCallback(d), state); 
        } 

 
        /// 
        ///     Optional override for subclasses, for responding to notification that operation is starting.
        /// 
        public virtual void OperationStarted() 
        {
        } 
 
        /// 
        ///     Optional override for subclasses, for responding to notification that operation has completed. 
        /// 
        public virtual void OperationCompleted()
        {
        } 

        // Method called when the CLR does a wait operation 
        [CLSCompliant(false)] 
        [PrePrepareMethod]
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags =SecurityPermissionFlag.ControlPolicy|SecurityPermissionFlag.ControlEvidence)] 
        public virtual int Wait(IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout)
        {
            if (waitHandles == null)
            { 
                throw new ArgumentNullException("waitHandles");
            } 
            return WaitHelper(waitHandles, waitAll, millisecondsTimeout); 
        }
 
        // Static helper to which the above method can delegate to in order to get the default
        // COM behavior.
        [CLSCompliant(false)]
        [PrePrepareMethod] 
        [MethodImplAttribute(MethodImplOptions.InternalCall)]
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags =SecurityPermissionFlag.ControlPolicy|SecurityPermissionFlag.ControlEvidence), 
        ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)] 
        protected static extern int WaitHelper(IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout);
 
        // set SynchronizationContext on the current thread
        [SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags =SecurityPermissionFlag.ControlPolicy|SecurityPermissionFlag.ControlEvidence)]
        public static void SetSynchronizationContext(SynchronizationContext syncContext)
        { 
            SetSynchronizationContext(syncContext, Thread.CurrentThread.ExecutionContext.SynchronizationContext);
        } 
 
        internal static SynchronizationContextSwitcher SetSynchronizationContext(SynchronizationContext syncContext, SynchronizationContext prevSyncContext)
        { 
            // get current execution context
            ExecutionContext ec = Thread.CurrentThread.ExecutionContext;
            // create a swticher
            SynchronizationContextSwitcher scsw = new SynchronizationContextSwitcher(); 

            RuntimeHelpers.PrepareConstrainedRegions(); 
            try 
            {
                // attach the switcher to the exec context 
                scsw._ec = ec;
                // save the current sync context using the passed in value
                scsw.savedSC = prevSyncContext;
                // save the new sync context also 
                scsw.currSC = syncContext;
                // update the current sync context to the new context 
                ec.SynchronizationContext = syncContext; 
            }
            catch 
            {
                // Any exception means we just restore the old SyncCtx
                scsw.UndoNoThrow(); //No exception will be thrown in this Undo()
                throw; 
            }
            // return switcher 
            return scsw; 
        }
 
        // Get the current SynchronizationContext on the current thread
        public static SynchronizationContext Current
        {
            get 
            {
                ExecutionContext ec = Thread.CurrentThread.GetExecutionContextNoCreate(); 
                if (ec != null) 
                    return ec.SynchronizationContext;
                return null; 
            }
        }

        // helper to Clone this SynchronizationContext, 
        public virtual SynchronizationContext CreateCopy()
        { 
            // the CLR dummy has an empty clone function - no member data 
            return new SynchronizationContext();
        } 

        private static int InvokeWaitMethodHelper(SynchronizationContext syncContext, IntPtr[] waitHandles, bool waitAll, int millisecondsTimeout)
        {
            return syncContext.Wait(waitHandles, waitAll, millisecondsTimeout); 
        }
    } 
} 

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