Code:
/ FX-1434 / FX-1434 / 1.0 / untmp / whidbey / REDBITS / ndp / fx / src / WinForms / Managed / System / WinForms / WindowsFormsSynchronizationContext.cs / 1 / 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 sync 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 sync 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 sync 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 sync 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. // Copyright (c) Microsoft Corporation. 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