Code:
/ 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Base / MS / Internal / ShutDownListener.cs / 1305600 / ShutDownListener.cs
//---------------------------------------------------------------------------- // //// Copyright (C) Microsoft Corporation. All rights reserved. // // // Description: Listen for shut down events on behalf of a target, in a way that // does not leak the target. ShutDown events include: // AppDomain.DomainUnload // AppDomain.ProcessExit // Dispatcher.ShutdownFinished // Listening to these events directly can cause leaks, since the AppDomain // lives longer than the target. // // The WeakEvent pattern has similar goals, but can't be used here because // the WeakEvent table itself needs to listen for shutdown events. // // "Target" refers to the actual consumer of the event(s). Each class // XYZ that wants to consume these events should define a class // XYZShutDownListener deriving from ShutDownListener that overrides the // OnShutDown method. The target's constructor typically creates an // instance of the XYZShutDownListener, which holds a weak reference to // the target, and listens for the desired events. When an event occurs, // the OnShutDown override is passed a (normal) reference to the target // object, and typically calls an appropriate target method that reacts // to the event. (See examples in WeakEventTable, DataBindEngine, etc.) // // Shutdown is a "one-time" process. When the ShutDownListener receives // any one of the desired events, it stops listening to all events. //--------------------------------------------------------------------------- using System; using System.Security; // [SecurityCritical] using System.Threading; // Interlocked using System.Windows.Threading; // Dispatcher using MS.Internal.WindowsBase; // [FriendAccessAllowed] namespace MS.Internal { [FriendAccessAllowed] // defined in Base, also used in Framework [Flags] internal enum ShutDownEvents : ushort { DomainUnload = 0x0001, ProcessExit = 0x0002, DispatcherShutdown = 0x0004, AppDomain = DomainUnload | ProcessExit, All = AppDomain | DispatcherShutdown, } [FriendAccessAllowed] // defined in Base, also used in Framework internal abstract class ShutDownListener : WeakReference { ////// Critical - accesses AppDomain.DomainUnload event. /// not SecurityTreatAsSafe. /// [SecurityCritical] internal ShutDownListener(object target) : this(target, ShutDownEvents.All) { } ////// Critical - accesses AppDomain.DomainUnload and AppDomain.ProcessExit events (which have link demands). /// not SecurityTreatAsSafe. /// [SecurityCritical] internal ShutDownListener(object target, ShutDownEvents events) : base(target) { _flags = ((PrivateFlags)events) | PrivateFlags.Listening; if (target == null) { _flags |= PrivateFlags.Static; } if ((_flags & PrivateFlags.DomainUnload) != 0) { AppDomain.CurrentDomain.DomainUnload += new EventHandler(HandleShutDown); } if ((_flags & PrivateFlags.ProcessExit) != 0) { AppDomain.CurrentDomain.ProcessExit += new EventHandler(HandleShutDown); } if ((_flags & PrivateFlags.DispatcherShutdown) != 0) { Dispatcher dispatcher = Dispatcher.CurrentDispatcher; dispatcher.ShutdownFinished += new EventHandler(HandleShutDown); _dispatcherWR = new WeakReference(dispatcher); } } // derived class should override this method to inform the target that a shutdown // event has occurred. This method might be called on any thread (e.g. // AppDomain.DomainUnload events are typically raised on worker threads). abstract internal void OnShutDown(object target, object sender, EventArgs e); // stop listening for shutdown events ////// Critical: accesses AppDomain.DomainUnload event /// TreatAsSafe: This code does not take any parameter or return state. /// It simply unattaches private callbacks. /// [SecurityCritical,SecurityTreatAsSafe] internal void StopListening() { if ((_flags & PrivateFlags.Listening) == 0) return; _flags = _flags & ~PrivateFlags.Listening; if ((_flags & PrivateFlags.DomainUnload) != 0) { AppDomain.CurrentDomain.DomainUnload -= new EventHandler(HandleShutDown); } if ((_flags & PrivateFlags.ProcessExit) != 0) { AppDomain.CurrentDomain.ProcessExit -= new EventHandler(HandleShutDown); } if ((_flags & PrivateFlags.DispatcherShutdown) != 0) { Dispatcher dispatcher = (Dispatcher)_dispatcherWR.Target; if (dispatcher != null) { dispatcher.ShutdownFinished -= new EventHandler(HandleShutDown); } _dispatcherWR = null; } } // handle a shutdown event private void HandleShutDown(object sender, EventArgs e) { // The dispatcher and AppDomain events might arrive on separate threads // at the same time. The interlock assures that we only do the work // once. if (Interlocked.Exchange(ref _inShutDown, 1) == 0) { // ShutDown is a one-time event. Stop listening (thus releasing // references to the ShutDownListener). StopListening(); // do the shutdown work, unless the target has been GC'd already. object target = Target; if (target != null || (_flags & PrivateFlags.Static) != 0) { OnShutDown(target, sender, e); } } } [Flags] enum PrivateFlags : ushort { DomainUnload = ShutDownEvents.DomainUnload, ProcessExit = ShutDownEvents.ProcessExit, DispatcherShutdown = ShutDownEvents.DispatcherShutdown, Static = 0x4000, Listening = 0x8000, } PrivateFlags _flags; WeakReference _dispatcherWR; int _inShutDown; } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // Copyright (c) Microsoft Corporation. All rights reserved.
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