WindowsFormsSynchronizationContext.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / fx / src / WinForms / Managed / System / WinForms / WindowsFormsSynchronizationContext.cs / 1305376 / WindowsFormsSynchronizationContext.cs
                        
                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
//----------------------------------------------------------------------------- 

using System; 
using System.Threading; 
using System.Windows.Forms;
using System.Diagnostics; 
using System.ComponentModel;
using System.Security;
using System.Security.Permissions;
 
namespace System.Windows.Forms
{ 
    ///  
    /// 
    ///     SynchronizationContext subclass used by the Windows Forms package. 
    /// 
    public sealed class WindowsFormsSynchronizationContext : SynchronizationContext, IDisposable {
        private Control controlToSendTo;
        private WeakReference destinationThreadRef; 

        //ThreadStatics won't get initialized per thread: easiest to just invert the value. 
        [ThreadStatic] 
        private static bool dontAutoInstall;
 
        [ThreadStatic]
        private static bool inSyncContextInstallation;

        [ThreadStatic] 
        private static SynchronizationContext previousSyncContext;
 
 
        /// 
        public WindowsFormsSynchronizationContext() { 
            DestinationThread = Thread.CurrentThread;   //store the current thread to ensure its still alive during an invoke.
            Application.ThreadContext context = Application.ThreadContext.FromCurrent();
            Debug.Assert(context != null);
            if (context != null) { 
              controlToSendTo = context.MarshalingControl;
            } 
            Debug.Assert(controlToSendTo.IsHandleCreated, "Marshaling control should have created its handle in its ctor."); 
        }
 
        private WindowsFormsSynchronizationContext(Control marshalingControl, Thread destinationThread) {
            controlToSendTo = marshalingControl;
            this.DestinationThread = destinationThread;
            Debug.Assert(controlToSendTo.IsHandleCreated, "Marshaling control should have created its handle in its ctor."); 
        }
 
        // VSWhidbey 476889: Directly holding onto the Thread can prevent ThreadStatics from finalizing. 
        private Thread DestinationThread {
            get { 
                if ((destinationThreadRef != null) && (destinationThreadRef.IsAlive)) {
                    return destinationThreadRef.Target as Thread;
                }
                return null; 
            }
            set { 
                if (value != null) { 
                    destinationThreadRef = new WeakReference(value);
                } 
            }
        }
        public void Dispose() {
            if (controlToSendTo != null) { 
                if (!controlToSendTo.IsDisposed) {
                    controlToSendTo.Dispose(); 
                } 
                controlToSendTo = null;
            } 
        }

        /// 
        // This is never called because we decide whether to Send or Post and we always post 
        public override void Send(SendOrPostCallback d, Object state) {
            Thread destinationThread = DestinationThread; 
            if (destinationThread == null || !destinationThread.IsAlive) { 
                throw new InvalidAsynchronousStateException(SR.GetString(SR.ThreadNoLongerValid));
            } 

            Debug.Assert(controlToSendTo != null, "Should always have the marshaling control by this point");

            if (controlToSendTo != null) { 
                controlToSendTo.Invoke(d, new object[] { state });
            } 
        } 

        ///  
        public override void Post(SendOrPostCallback d, Object state) {
            Debug.Assert(controlToSendTo != null, "Should always have the marshaling control by this point");

            if (controlToSendTo != null) { 
                controlToSendTo.BeginInvoke(d, new object[] { state });
            } 
        } 

        ///  
        public override SynchronizationContext CreateCopy() {
            return new WindowsFormsSynchronizationContext(controlToSendTo, DestinationThread);
        }
 
        /// 
        // Determines whether we install the WindowsFormsSynchronizationContext when we create a control, or 
        // when we start a message loop.  Default: true. 
        [EditorBrowsable(EditorBrowsableState.Advanced)]
        public static bool AutoInstall { 
            get {
                return !dontAutoInstall;
            }
            set { 
                dontAutoInstall = !value;
            } 
        } 

        // Instantiate and install a WF op [....] context, and save off the old one. 
        internal static void InstallIfNeeded() {
            // Exit if we shouldn't auto-install, if we've already installed and we haven't uninstalled,
            // or if we're being called recursively (creating the WF
            // async op [....] context can create a parking window control). 
            if (!AutoInstall || inSyncContextInstallation) {
                return; 
            } 

            if (SynchronizationContext.Current == null) { 
                previousSyncContext = null;
            }

            if (previousSyncContext != null) { 
                return;
            } 
 
            inSyncContextInstallation = true;
            try { 
                SynchronizationContext currentContext = AsyncOperationManager.SynchronizationContext;
                //Make sure we either have no [....] context or that we have one of type SynchronizationContext
                if (currentContext == null || currentContext.GetType() == typeof(SynchronizationContext)) {
                    previousSyncContext = currentContext; 

                    // SECREVIEW : WindowsFormsSynchronizationContext.cctor generates a call to SetTopLevel on the MarshallingControl (hidden sycn hwnd), 
                    //             this call demands TopLevelWindow (UIPermissionWindow.SafeTopLevelWindows) so an assert for that permission is needed here. 
                    //             The assert is safe, we are creating a thread context and the [....] window is hidden.
                    new PermissionSet(PermissionState.Unrestricted).Assert(); 
                    try {
                        AsyncOperationManager.SynchronizationContext = new WindowsFormsSynchronizationContext();
                    }
                    finally { 
                        CodeAccessPermission.RevertAssert();
                    } 
                } 
            }
            finally { 
                inSyncContextInstallation = false;
            }
        }
 
        public static void Uninstall() {
            Uninstall(true); 
        } 

        internal static void Uninstall(bool turnOffAutoInstall) { 
            if (AutoInstall) {
                WindowsFormsSynchronizationContext winFormsSyncContext = AsyncOperationManager.SynchronizationContext as WindowsFormsSynchronizationContext;
                if (winFormsSyncContext != null) {
                    try { 
                        new PermissionSet(PermissionState.Unrestricted).Assert();
                        if (previousSyncContext == null) { 
                            AsyncOperationManager.SynchronizationContext = new SynchronizationContext(); 
                        }
                        else { 
                            AsyncOperationManager.SynchronizationContext = previousSyncContext;
                        }
                    }
                    finally { 
                        previousSyncContext = null;
                        CodeAccessPermission.RevertAssert(); 
                    } 
                }
            } 
            if (turnOffAutoInstall) {
                AutoInstall = false;
            }
        } 
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
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WindowsFormsSynchronizationContext.cs source code in C# .NET

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