Code:
/ Net / Net / 3.5.50727.3053 / DEVDIV / depot / DevDiv / releases / whidbey / netfxsp / ndp / clr / src / BCL / System / WeakReference.cs / 5 / WeakReference.cs
// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== /*============================================================ ** ** Class: WeakReference ** ** Purpose: A wrapper for establishing a WeakReference to an Object. ** ===========================================================*/ namespace System { using System; using System.Runtime.Remoting; using System.Runtime.Serialization; using System.Security.Permissions; using System.Runtime.InteropServices; using System.Threading; [System.Runtime.InteropServices.ComVisible(true)] [SecurityPermissionAttribute(SecurityAction.InheritanceDemand, Flags=SecurityPermissionFlag.UnmanagedCode)] [Serializable()] public class WeakReference : ISerializable { // Most methods using m_handle should use GC.KeepAlive(this) // to avoid potential handle recycling attacks. The GC special // cases the finalizer for WeakReference & only clears them // when all threads are suspended, but you might still run into // problems if your code is at least partially interruptible. // It's just too much complexity to think about. internal volatile IntPtr m_handle; internal bool m_IsLongReference; // Creates a new WeakReference that keeps track of target. // Assumes a Short Weak Reference (ie TrackResurrection is false.) // public WeakReference(Object target) : this(target, false) { } //Creates a new WeakReference that keeps track of target. // public WeakReference(Object target, bool trackResurrection) { m_IsLongReference=trackResurrection; m_handle = GCHandle.InternalAlloc(target, trackResurrection ? GCHandleType.WeakTrackResurrection : GCHandleType.Weak); } protected WeakReference(SerializationInfo info, StreamingContext context) { if (info==null) { throw new ArgumentNullException("info"); } Object temp = info.GetValue("TrackedObject",typeof(Object)); m_IsLongReference = info.GetBoolean("TrackResurrection"); m_handle = GCHandle.InternalAlloc(temp, m_IsLongReference ? GCHandleType.WeakTrackResurrection : GCHandleType.Weak); } //Determines whether or not this instance of WeakReference still refers to an object //that has not been collected. // public virtual bool IsAlive { get { IntPtr h = m_handle; // In determining whether it is valid to use this object, we need to at least expose this // without throwing an exception. if (IntPtr.Zero == h) return false; bool result = (GCHandle.InternalGet(h)!=null); // We want to ensure that if the target is live, then we will // return it to the user. We need to keep this WeakReference object // live so m_handle doesn't get set to 0 or reused. // Since m_handle is volatile, the following statement will // guarantee the weakref object is live till the following // statement. return (m_handle == IntPtr.Zero) ? false : result; } } //Returns a boolean indicating whether or not we're tracking objects until they're collected (true) //or just until they're finalized (false). // public virtual bool TrackResurrection { get { return m_IsLongReference; } } //Gets the Object stored in the handle if it's accessible. // Or sets it. // public virtual Object Target { get { IntPtr h = m_handle; // Should only happen when used illegally, like using a // WeakReference from a finalizer. if (IntPtr.Zero == h) return null; Object o = GCHandle.InternalGet(h); // We want to ensure that if the target is live, then we will // return it to the user. We need to keep this WeakReference object // live so m_handle doesn't get set to 0 or reused. // Since m_handle is volatile, the following statement will // guarantee the weakref object is live till the following // statement. return (m_handle == IntPtr.Zero) ? null : o; } set { IntPtr h = m_handle; if (h == IntPtr.Zero) throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HandleIsNotInitialized")); // There is a ---- w/ finalization where m_handle gets set to // NULL and the WeakReference becomes invalid. Here we have to // do the following in order: // // 1. Get the old object value // 2. Get m_handle // 3. HndInterlockedCompareExchange(m_handle, newValue, oldValue); // // If the interlocked-cmp-exchange fails, then either we lost a ---- // with another updater, or we lost a ---- w/ the finalizer. In // either case, we can just let the other guy win. Object oldValue = GCHandle.InternalGet(h); h = m_handle; if (h == IntPtr.Zero) throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HandleIsNotInitialized")); GCHandle.InternalCompareExchange(h, value, oldValue, false /* isPinned */); // Ensure we don't have any handle recycling attacks in this // method where the finalizer frees the handle. GC.KeepAlive(this); } } // Free all system resources associated with this reference. // // Note: The WeakReference finalizer is not actually run, but // treated specially in gc.cpp's ScanForFinalization // This is needed for subclasses deriving from WeakReference, however. #pragma warning disable 420 ~WeakReference() { IntPtr old_handle = m_handle; if (old_handle != IntPtr.Zero) { if (old_handle == Interlocked.CompareExchange(ref m_handle, IntPtr.Zero, old_handle)) GCHandle.InternalFree(old_handle); } } public virtual void GetObjectData(SerializationInfo info, StreamingContext context) { if (info==null) { throw new ArgumentNullException("info"); } info.AddValue("TrackedObject", Target, typeof(Object)); info.AddValue("TrackResurrection", m_IsLongReference); } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007. // ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== /*============================================================ ** ** Class: WeakReference ** ** Purpose: A wrapper for establishing a WeakReference to an Object. ** ===========================================================*/ namespace System { using System; using System.Runtime.Remoting; using System.Runtime.Serialization; using System.Security.Permissions; using System.Runtime.InteropServices; using System.Threading; [System.Runtime.InteropServices.ComVisible(true)] [SecurityPermissionAttribute(SecurityAction.InheritanceDemand, Flags=SecurityPermissionFlag.UnmanagedCode)] [Serializable()] public class WeakReference : ISerializable { // Most methods using m_handle should use GC.KeepAlive(this) // to avoid potential handle recycling attacks. The GC special // cases the finalizer for WeakReference & only clears them // when all threads are suspended, but you might still run into // problems if your code is at least partially interruptible. // It's just too much complexity to think about. internal volatile IntPtr m_handle; internal bool m_IsLongReference; // Creates a new WeakReference that keeps track of target. // Assumes a Short Weak Reference (ie TrackResurrection is false.) // public WeakReference(Object target) : this(target, false) { } //Creates a new WeakReference that keeps track of target. // public WeakReference(Object target, bool trackResurrection) { m_IsLongReference=trackResurrection; m_handle = GCHandle.InternalAlloc(target, trackResurrection ? GCHandleType.WeakTrackResurrection : GCHandleType.Weak); } protected WeakReference(SerializationInfo info, StreamingContext context) { if (info==null) { throw new ArgumentNullException("info"); } Object temp = info.GetValue("TrackedObject",typeof(Object)); m_IsLongReference = info.GetBoolean("TrackResurrection"); m_handle = GCHandle.InternalAlloc(temp, m_IsLongReference ? GCHandleType.WeakTrackResurrection : GCHandleType.Weak); } //Determines whether or not this instance of WeakReference still refers to an object //that has not been collected. // public virtual bool IsAlive { get { IntPtr h = m_handle; // In determining whether it is valid to use this object, we need to at least expose this // without throwing an exception. if (IntPtr.Zero == h) return false; bool result = (GCHandle.InternalGet(h)!=null); // We want to ensure that if the target is live, then we will // return it to the user. We need to keep this WeakReference object // live so m_handle doesn't get set to 0 or reused. // Since m_handle is volatile, the following statement will // guarantee the weakref object is live till the following // statement. return (m_handle == IntPtr.Zero) ? false : result; } } //Returns a boolean indicating whether or not we're tracking objects until they're collected (true) //or just until they're finalized (false). // public virtual bool TrackResurrection { get { return m_IsLongReference; } } //Gets the Object stored in the handle if it's accessible. // Or sets it. // public virtual Object Target { get { IntPtr h = m_handle; // Should only happen when used illegally, like using a // WeakReference from a finalizer. if (IntPtr.Zero == h) return null; Object o = GCHandle.InternalGet(h); // We want to ensure that if the target is live, then we will // return it to the user. We need to keep this WeakReference object // live so m_handle doesn't get set to 0 or reused. // Since m_handle is volatile, the following statement will // guarantee the weakref object is live till the following // statement. return (m_handle == IntPtr.Zero) ? null : o; } set { IntPtr h = m_handle; if (h == IntPtr.Zero) throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HandleIsNotInitialized")); // There is a ---- w/ finalization where m_handle gets set to // NULL and the WeakReference becomes invalid. Here we have to // do the following in order: // // 1. Get the old object value // 2. Get m_handle // 3. HndInterlockedCompareExchange(m_handle, newValue, oldValue); // // If the interlocked-cmp-exchange fails, then either we lost a ---- // with another updater, or we lost a ---- w/ the finalizer. In // either case, we can just let the other guy win. Object oldValue = GCHandle.InternalGet(h); h = m_handle; if (h == IntPtr.Zero) throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_HandleIsNotInitialized")); GCHandle.InternalCompareExchange(h, value, oldValue, false /* isPinned */); // Ensure we don't have any handle recycling attacks in this // method where the finalizer frees the handle. GC.KeepAlive(this); } } // Free all system resources associated with this reference. // // Note: The WeakReference finalizer is not actually run, but // treated specially in gc.cpp's ScanForFinalization // This is needed for subclasses deriving from WeakReference, however. #pragma warning disable 420 ~WeakReference() { IntPtr old_handle = m_handle; if (old_handle != IntPtr.Zero) { if (old_handle == Interlocked.CompareExchange(ref m_handle, IntPtr.Zero, old_handle)) GCHandle.InternalFree(old_handle); } } public virtual void GetObjectData(SerializationInfo info, StreamingContext context) { if (info==null) { throw new ArgumentNullException("info"); } info.AddValue("TrackedObject", Target, typeof(Object)); info.AddValue("TrackResurrection", m_IsLongReference); } } } // File provided for Reference Use Only by Microsoft Corporation (c) 2007.
Link Menu
This book is available now!
Buy at Amazon US or
Buy at Amazon UK
- DesignTimeHTMLTextWriter.cs
- NativeCompoundFileAPIs.cs
- FontFaceLayoutInfo.cs
- ListCollectionView.cs
- UriTemplateTrieLocation.cs
- RequestQueue.cs
- TerminatorSinks.cs
- XsltLibrary.cs
- AlphabeticalEnumConverter.cs
- SerializationInfo.cs
- TextBlockAutomationPeer.cs
- SystemColors.cs
- SmiSettersStream.cs
- IfElseDesigner.xaml.cs
- SAPIEngineTypes.cs
- ControlValuePropertyAttribute.cs
- DoubleAnimationUsingPath.cs
- MediaPlayerState.cs
- XmlSerializerFactory.cs
- StreamWithDictionary.cs
- LinkArea.cs
- BigInt.cs
- Utils.cs
- TextCompositionManager.cs
- ActivityUtilities.cs
- EntityContainer.cs
- SQLBinaryStorage.cs
- HttpAsyncResult.cs
- WeakEventManager.cs
- NonDualMessageSecurityOverHttp.cs
- Converter.cs
- NameScopePropertyAttribute.cs
- Camera.cs
- DisableDpiAwarenessAttribute.cs
- RemotingConfiguration.cs
- Opcode.cs
- InvalidWMPVersionException.cs
- PlanCompilerUtil.cs
- PropertyDescriptor.cs
- ColumnMapVisitor.cs
- ShellProvider.cs
- CodeConstructor.cs
- XmlSerializerVersionAttribute.cs
- ToolStrip.cs
- SqlDataAdapter.cs
- InputLangChangeRequestEvent.cs
- TransformerInfo.cs
- DetailsViewInsertedEventArgs.cs
- BinaryObjectWriter.cs
- XmlEnumAttribute.cs
- prefixendpointaddressmessagefilter.cs
- TimeSpan.cs
- XmlArrayAttribute.cs
- X509SecurityTokenProvider.cs
- BindingElementExtensionElement.cs
- DataBindingHandlerAttribute.cs
- CharEnumerator.cs
- PlaceHolder.cs
- StylusTip.cs
- SplitContainer.cs
- ValidatorCompatibilityHelper.cs
- ApplyImportsAction.cs
- UnSafeCharBuffer.cs
- HMACSHA1.cs
- QilTypeChecker.cs
- QueryStringParameter.cs
- DataBindingCollection.cs
- Context.cs
- util.cs
- StateRuntime.cs
- XmlSchemaCompilationSettings.cs
- BuildProvider.cs
- BitmapEffect.cs
- SHA384.cs
- ChangeInterceptorAttribute.cs
- PropertyEmitterBase.cs
- RepeaterCommandEventArgs.cs
- DefaultBindingPropertyAttribute.cs
- XPathMultyIterator.cs
- QilParameter.cs
- Pen.cs
- Win32Exception.cs
- HighlightComponent.cs
- MutexSecurity.cs
- UriTemplateTable.cs
- RuntimeResourceSet.cs
- SchemaImporter.cs
- DefaultValidator.cs
- MULTI_QI.cs
- documentsequencetextpointer.cs
- TextChangedEventArgs.cs
- ReadOnlyTernaryTree.cs
- LogLogRecordHeader.cs
- XmlImplementation.cs
- DebugViewWriter.cs
- SrgsElementList.cs
- TreeViewImageKeyConverter.cs
- Trustee.cs
- Image.cs
- HyperLinkField.cs