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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
/*============================================================
**
**
** Purpose: A wrapper for establishing a WeakReference to a generic type.
**
===========================================================*/
namespace System
{
using System;
using System.Runtime.Serialization;
using System.Security;
using System.Runtime;
using System.Runtime.CompilerServices;
using System.Runtime.Versioning;
using System.Diagnostics.Contracts;
#if FEATURE_SERIALIZATION
[Serializable]
#endif
// This class is sealed to mitigate security issues caused by Object::MemberwiseClone.
public sealed class WeakReference<T> : ISerializable where T : class
{
// If you fix bugs here, please fix them in WeakReference at the same time.
// This field is not a regular GC handle. It can have a special values that are used to prevent a race condition between setting the target and finalization.
internal IntPtr m_handle;
// Creates a new WeakReference that keeps track of target.
// Assumes a Short Weak Reference (ie TrackResurrection is false.)
//
public WeakReference(T target)
: this(target, false)
{
}
//Creates a new WeakReference that keeps track of target.
//
public WeakReference(T target, bool trackResurrection)
{
Create(target, trackResurrection);
}
internal WeakReference(SerializationInfo info, StreamingContext context)
{
if (info == null) {
throw new ArgumentNullException("info");
}
Contract.EndContractBlock();
T target = (T)info.GetValue("TrackedObject", typeof(T));
bool trackResurrection = info.GetBoolean("TrackResurrection");
Create(target, trackResurrection);
}
//
// We are exposing TryGetTarget instead of a simple getter to avoid a common problem where people write incorrect code like:
//
// WeakReference ref = ...;
// if (ref.Target != null)
// DoSomething(ref.Target)
//
[MethodImplAttribute(MethodImplOptions.AggressiveInlining)]
public bool TryGetTarget(out T target)
{
// Call the worker method that has more performant but less user friendly signature.
T o = this.Target;
target = o;
return o != null;
}
public void SetTarget(T target)
{
this.Target = target;
}
// This is property for better debugging experience (VS debugger shows values of properties when you hover over the variables)
private extern T Target
{
[MethodImplAttribute(MethodImplOptions.InternalCall)]
[SecuritySafeCritical]
get;
[MethodImplAttribute(MethodImplOptions.InternalCall)]
[SecuritySafeCritical]
set;
}
// Free all system resources associated with this reference.
//
// Note: The WeakReference<T> finalizer is not usually run, but
// treated specially in gc.cpp's ScanForFinalization
// This is needed for subclasses deriving from WeakReference<T>, however.
// Additionally, there may be some cases during shutdown when we run this finalizer.
[MethodImplAttribute(MethodImplOptions.InternalCall)]
[SecuritySafeCritical]
extern ~WeakReference();
[SecurityCritical]
public void GetObjectData(SerializationInfo info, StreamingContext context)
{
if (info == null) {
throw new ArgumentNullException("info");
}
Contract.EndContractBlock();
info.AddValue("TrackedObject", this.Target, typeof(T));
info.AddValue("TrackResurrection", IsTrackResurrection());
}
[MethodImplAttribute(MethodImplOptions.InternalCall)]
[SecuritySafeCritical]
private extern void Create(T target, bool trackResurrection);
[MethodImplAttribute(MethodImplOptions.InternalCall)]
[SecuritySafeCritical]
private extern bool IsTrackResurrection();
}
}
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