Code:
/ 4.0 / 4.0 / DEVDIV_TFS / Dev10 / Releases / RTMRel / ndp / clr / src / BCL / System / WeakReference.cs / 1305376 / 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; using System.Diagnostics.Contracts; [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; #if FEATURE_CORECLR // Migrating InheritanceDemands requires this default ctor, so we can mark it SafeCritical protected WeakReference() { Contract.Assert(false, "WeakReferences protected default ctor should never be used!"); throw new NotImplementedException(); } #endif // 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. // [System.Security.SecuritySafeCritical] // auto-generated public WeakReference(Object target, bool trackResurrection) { m_IsLongReference=trackResurrection; m_handle = GCHandle.InternalAlloc(target, trackResurrection ? GCHandleType.WeakTrackResurrection : GCHandleType.Weak); } [System.Security.SecuritySafeCritical] // auto-generated protected WeakReference(SerializationInfo info, StreamingContext context) { if (info==null) { throw new ArgumentNullException("info"); } Contract.EndContractBlock(); 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 { [System.Security.SecuritySafeCritical] // auto-generated 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 { [System.Security.SecuritySafeCritical] // auto-generated 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; } [System.Security.SecuritySafeCritical] // auto-generated 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 [System.Security.SecuritySafeCritical] // auto-generated ~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); } } [System.Security.SecurityCritical] public virtual void GetObjectData(SerializationInfo info, StreamingContext context) { if (info==null) { throw new ArgumentNullException("info"); } Contract.EndContractBlock(); 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; using System.Diagnostics.Contracts; [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; #if FEATURE_CORECLR // Migrating InheritanceDemands requires this default ctor, so we can mark it SafeCritical protected WeakReference() { Contract.Assert(false, "WeakReferences protected default ctor should never be used!"); throw new NotImplementedException(); } #endif // 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. // [System.Security.SecuritySafeCritical] // auto-generated public WeakReference(Object target, bool trackResurrection) { m_IsLongReference=trackResurrection; m_handle = GCHandle.InternalAlloc(target, trackResurrection ? GCHandleType.WeakTrackResurrection : GCHandleType.Weak); } [System.Security.SecuritySafeCritical] // auto-generated protected WeakReference(SerializationInfo info, StreamingContext context) { if (info==null) { throw new ArgumentNullException("info"); } Contract.EndContractBlock(); 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 { [System.Security.SecuritySafeCritical] // auto-generated 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 { [System.Security.SecuritySafeCritical] // auto-generated 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; } [System.Security.SecuritySafeCritical] // auto-generated 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 [System.Security.SecuritySafeCritical] // auto-generated ~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); } } [System.Security.SecurityCritical] public virtual void GetObjectData(SerializationInfo info, StreamingContext context) { if (info==null) { throw new ArgumentNullException("info"); } Contract.EndContractBlock(); 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
- WebControlAdapter.cs
- ISAPIApplicationHost.cs
- SuppressMessageAttribute.cs
- DiscoveryInnerClientAdhocCD1.cs
- MaskedTextProvider.cs
- TimeSpanValidatorAttribute.cs
- XsltConvert.cs
- RegionInfo.cs
- ProcessRequestArgs.cs
- FontStretchConverter.cs
- indexingfiltermarshaler.cs
- VoiceInfo.cs
- TransformationRules.cs
- ColumnMapVisitor.cs
- XmlSchemaObjectCollection.cs
- SortKey.cs
- HttpCachePolicyBase.cs
- RegexRunner.cs
- StringToken.cs
- StylusButtonEventArgs.cs
- StorageAssociationTypeMapping.cs
- AnnotationService.cs
- PropertyReferenceSerializer.cs
- HideDisabledControlAdapter.cs
- CodeDomSerializer.cs
- SvcMapFileLoader.cs
- ChangesetResponse.cs
- COM2Properties.cs
- DesignerExtenders.cs
- ProgressBar.cs
- PageTheme.cs
- UnsafeNativeMethods.cs
- HelloMessageApril2005.cs
- WebResourceAttribute.cs
- PointLight.cs
- ResizeGrip.cs
- DataBindingCollection.cs
- PageCache.cs
- PropertyRef.cs
- BindableTemplateBuilder.cs
- Win32SafeHandles.cs
- Not.cs
- DetailsViewInsertedEventArgs.cs
- ComponentGuaranteesAttribute.cs
- CookielessHelper.cs
- BitmapScalingModeValidation.cs
- DataColumnChangeEvent.cs
- FlowLayoutPanel.cs
- XmlArrayItemAttribute.cs
- HttpCookiesSection.cs
- EventProvider.cs
- InvalidProgramException.cs
- SQLInt32Storage.cs
- DbSourceCommand.cs
- DataGridHeadersVisibilityToVisibilityConverter.cs
- GrammarBuilderBase.cs
- FirstQueryOperator.cs
- RSAPKCS1KeyExchangeDeformatter.cs
- ScrollBar.cs
- RemotingConfiguration.cs
- PolygonHotSpot.cs
- DataGridViewSelectedCellsAccessibleObject.cs
- NominalTypeEliminator.cs
- ByteStreamMessageEncodingElement.cs
- Utils.cs
- InvalidEnumArgumentException.cs
- DesignerHierarchicalDataSourceView.cs
- NamespaceList.cs
- HtmlElementCollection.cs
- MissingSatelliteAssemblyException.cs
- AddressHeader.cs
- TransformGroup.cs
- ListParagraph.cs
- ThrowHelper.cs
- ViewRendering.cs
- GridViewHeaderRowPresenter.cs
- AdornerHitTestResult.cs
- ArrangedElement.cs
- InvalidWMPVersionException.cs
- XmlAtomicValue.cs
- QueueProcessor.cs
- SQLByteStorage.cs
- CompiledRegexRunnerFactory.cs
- ToolStripRenderEventArgs.cs
- TemplateBuilder.cs
- Automation.cs
- WindowHideOrCloseTracker.cs
- ListView.cs
- DecimalAnimationUsingKeyFrames.cs
- SqlFlattener.cs
- TemplateField.cs
- AssociationProvider.cs
- StreamResourceInfo.cs
- SessionParameter.cs
- HybridObjectCache.cs
- NullableLongMinMaxAggregationOperator.cs
- UnhandledExceptionEventArgs.cs
- ClientScriptItemCollection.cs
- BookmarkNameHelper.cs
- IntegerValidatorAttribute.cs