Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/mscorlib/system/weakreference.cs

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+// ==++==
+// 
+//   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.Serialization;
+    using System.Security;
+    using System.Security.Permissions;
+    using System.Runtime.CompilerServices;
+    using System.Runtime.Versioning;
+    using System.Diagnostics.Contracts;
+    [System.Runtime.InteropServices.ComVisible(true)]
+#if !FEATURE_CORECLR
+    [SecurityPermissionAttribute(SecurityAction.InheritanceDemand, Flags=SecurityPermissionFlag.UnmanagedCode)] // Don't call Object::MemberwiseClone.
+#endif
+    [Serializable]
+    public class WeakReference : ISerializable {
+        // If you fix bugs here, please fix them in WeakReference<T> at the same time.
+
+        // This field is not a regular GC handle. It can have a special values that are used to prevent ----s between setting the target and finalization.
+        internal IntPtr m_handle;
+    
+#if FEATURE_CORECLR
+        // Migrating InheritanceDemands requires this default ctor, so we can mark it SafeCritical
+        [SecuritySafeCritical]
+        protected WeakReference() {
+            Contract.Assert(false, "WeakReference's 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.
+        //
+        public WeakReference(Object target, bool trackResurrection) {
+            Create(target, trackResurrection);
+        }
+
+        protected WeakReference(SerializationInfo info, StreamingContext context) {
+            if (info==null) {
+                throw new ArgumentNullException("info");
+            }
+            Contract.EndContractBlock();
+
+            Object target = info.GetValue("TrackedObject",typeof(Object));
+            bool trackResurrection = info.GetBoolean("TrackResurrection");
+
+            Create(target, trackResurrection);
+        }
+    
+        //Determines whether or not this instance of WeakReference still refers to an object
+        //that has not been collected.
+        //
+        public extern virtual bool IsAlive {
+            [ResourceExposure(ResourceScope.None)]
+            [MethodImplAttribute(MethodImplOptions.InternalCall)]
+            [SecuritySafeCritical]
+            get;
+         }
+    
+        //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 {
+            // We need to call IsTrackResurrection non-virtually in GetObjectData, and so the virtual property cannot be FCall directly
+            get { return IsTrackResurrection(); }
+        }
+
+        //Gets the Object stored in the handle if it's accessible.
+        // Or sets it.
+        //
+        public extern virtual Object Target {
+            [ResourceExposure(ResourceScope.None)]
+            [MethodImplAttribute(MethodImplOptions.InternalCall)]
+            [SecuritySafeCritical]
+            get;
+            [ResourceExposure(ResourceScope.None)]
+            [MethodImplAttribute(MethodImplOptions.InternalCall)]
+            [SecuritySafeCritical]
+            set;
+        }
+    
+        // 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.
+        // Additionally, there may be some cases during shutdown when we run this finalizer.
+        [ResourceExposure(ResourceScope.None)]
+        [MethodImplAttribute(MethodImplOptions.InternalCall)]
+        [SecuritySafeCritical]
+        extern ~WeakReference();
+
+        [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", IsTrackResurrection());
+        }
+
+        [ResourceExposure(ResourceScope.None)]
+        [MethodImplAttribute(MethodImplOptions.InternalCall)]
+        [SecuritySafeCritical]
+        private extern void Create(Object target, bool trackResurrection);
+
+        [ResourceExposure(ResourceScope.None)]
+        [MethodImplAttribute(MethodImplOptions.InternalCall)]
+        [SecuritySafeCritical]
+        private extern bool IsTrackResurrection();
+    }
+
+}