Code:
/ 4.0 / 4.0 / untmp / 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.
Link Menu
This book is available now!
Buy at Amazon US or
Buy at Amazon UK
- SQLBinary.cs
- TagPrefixInfo.cs
- KnownColorTable.cs
- TypeInitializationException.cs
- AnnouncementDispatcherAsyncResult.cs
- SourceFileInfo.cs
- GeneralTransform3D.cs
- SelectQueryOperator.cs
- OperatingSystem.cs
- OleCmdHelper.cs
- GeneralTransform3D.cs
- ClassDataContract.cs
- ProtectedProviderSettings.cs
- NotificationContext.cs
- safelink.cs
- ObjectDataSourceDesigner.cs
- XmlMemberMapping.cs
- AllMembershipCondition.cs
- NativeWindow.cs
- SortQuery.cs
- Zone.cs
- DoubleAnimationClockResource.cs
- NonParentingControl.cs
- TreeNodeStyleCollection.cs
- NegotiateStream.cs
- XmlTypeAttribute.cs
- DesignerCatalogPartChrome.cs
- ProtocolsConfiguration.cs
- Knowncolors.cs
- XsdDataContractImporter.cs
- FieldBuilder.cs
- ContractUtils.cs
- WebPartDisplayModeEventArgs.cs
- XmlQueryCardinality.cs
- OutputCacheSection.cs
- COM2IDispatchConverter.cs
- ClaimComparer.cs
- CloudCollection.cs
- PointAnimationClockResource.cs
- ObjectView.cs
- HMACSHA256.cs
- AggregateException.cs
- NetDataContractSerializer.cs
- DbProviderConfigurationHandler.cs
- TextBoxAutomationPeer.cs
- HttpRawResponse.cs
- InstanceOwnerQueryResult.cs
- InfoCardRSAPKCS1KeyExchangeDeformatter.cs
- PDBReader.cs
- Triplet.cs
- MediaEntryAttribute.cs
- oledbmetadatacollectionnames.cs
- DataIdProcessor.cs
- MultitargetUtil.cs
- SqlTypeConverter.cs
- ParseNumbers.cs
- MessagePropertyFilter.cs
- XhtmlCssHandler.cs
- EntityDataSourceState.cs
- WorkflowMarkupSerializerMapping.cs
- BCLDebug.cs
- GridItemProviderWrapper.cs
- VectorAnimation.cs
- ReaderWriterLockWrapper.cs
- WinEventHandler.cs
- RangeValuePatternIdentifiers.cs
- Icon.cs
- OptimisticConcurrencyException.cs
- ControlHelper.cs
- EventLogEntryCollection.cs
- XamlBrushSerializer.cs
- ZoneLinkButton.cs
- Table.cs
- FormViewPagerRow.cs
- wmiprovider.cs
- TemplatePropertyEntry.cs
- CodeCatchClauseCollection.cs
- ObjectList.cs
- RadioButton.cs
- OperationResponse.cs
- Hash.cs
- SourceCollection.cs
- NumericUpDownAcceleration.cs
- CqlLexer.cs
- PrtCap_Public_Simple.cs
- AuthenticationManager.cs
- CommonProperties.cs
- Vector3DValueSerializer.cs
- ScriptHandlerFactory.cs
- EntityRecordInfo.cs
- UnsafeNativeMethodsCLR.cs
- DCSafeHandle.cs
- GlyphManager.cs
- MemberInfoSerializationHolder.cs
- X509ChainElement.cs
- ProcessThreadCollection.cs
- MD5.cs
- InsufficientMemoryException.cs
- ExpressionBindings.cs
- TablePatternIdentifiers.cs