1 files changed, 76 insertions, 0 deletions
diff --git a/src/System.Private.CoreLib/shared/System/Gen2GcCallback.cs b/src/System.Private.CoreLib/shared/System/Gen2GcCallback.cs
new file mode 100644
index 000000000..225268122
--- /dev/null
+++ b/src/System.Private.CoreLib/shared/System/Gen2GcCallback.cs
@@ -0,0 +1,76 @@
+// 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);
+            }
+        }
+    }
+}