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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.
using System.Runtime.ConstrainedExecution;
using System.Runtime.InteropServices;
namespace System
{
/// <summary>
/// Schedules a callback roughly every gen 2 GC (you may see a Gen 0 an Gen 1 but only once)
/// (We can fix this by capturing the Gen 2 count at startup and testing, but I mostly don't care)
/// </summary>
internal sealed class Gen2GcCallback : CriticalFinalizerObject
{
private Gen2GcCallback()
: base()
{
}
/// <summary>
/// Schedule 'callback' to be called in the next GC. If the callback returns true it is
/// rescheduled for the next Gen 2 GC. Otherwise the callbacks stop.
///
/// NOTE: This callback will be kept alive until either the callback function returns false,
/// or the target object dies.
/// </summary>
public static void Register(Func<object, bool> callback, object targetObj)
{
// Create a unreachable object that remembers the callback function and target object.
Gen2GcCallback gcCallback = new Gen2GcCallback();
gcCallback.Setup(callback, targetObj);
}
private Func<object, bool> _callback;
private GCHandle _weakTargetObj;
private void Setup(Func<object, bool> callback, object targetObj)
{
_callback = callback;
_weakTargetObj = GCHandle.Alloc(targetObj, GCHandleType.Weak);
}
~Gen2GcCallback()
{
// Check to see if the target object is still alive.
object targetObj = _weakTargetObj.Target;
if (targetObj == null)
{
// The target object is dead, so this callback object is no longer needed.
_weakTargetObj.Free();
return;
}
// Execute the callback method.
try
{
if (!_callback(targetObj))
{
// If the callback returns false, this callback object is no longer needed.
return;
}
}
catch
{
// Ensure that we still get a chance to resurrect this object, even if the callback throws an exception.
}
// Resurrect ourselves by re-registering for finalization.
if (!Environment.HasShutdownStarted)
{
GC.ReRegisterForFinalize(this);
}
}
}
}
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