handle race

Author: majocha

src/Compiler/Utilities/Caches.fs

@@ -215,13 +215,10 @@ type Cache<'Key, 'Value when 'Key: not null and 'Key: equality> internal (totalC
                     async {
                         match! mb.Receive() with
                         | EvictionQueueMessage.Add entity ->
-
-                            assert entity.Node.IsSome
-
-                            evictionQueue.AddLast(entity.Node.Value)
+                            evictionQueue.AddLast(entity.Node)
 
                             // Evict one immediately if necessary.
-                            while evictionQueue.Count > capacity do
+                            if evictionQueue.Count > capacity then
                                 let first = nonNull evictionQueue.First
 
                                 match store.TryRemove(first.Value.Key) with
@@ -232,16 +229,13 @@ type Cache<'Key, 'Value when 'Key: not null and 'Key: equality> internal (totalC
                                     evicted.Trigger()
                                 | _ -> evictionFails.Add 1L
 
-                        | EvictionQueueMessage.Update entity ->
-                            entity.AccessCount <- entity.AccessCount + 1L
+                        // Store updates are not synchronized. It is possible the entity is no longer in the queue.
+                        | EvictionQueueMessage.Update entity when isNull entity.Node.List -> ()
 
-                            assert entity.Node.IsSome
-
-                            let node = entity.Node.Value
-                            assert (node.List = evictionQueue)
+                        | EvictionQueueMessage.Update entity ->
                             // Just move this node to the end of the list.
-                            evictionQueue.Remove(node)
-                            evictionQueue.AddLast(node)
+                            evictionQueue.Remove(entity.Node)
+                            evictionQueue.AddLast(entity.Node)
 
                         return! processNext ()
                     }
@@ -256,25 +250,27 @@ type Cache<'Key, 'Value when 'Key: not null and 'Key: equality> internal (totalC
 
     member _.TryGetValue(key: 'Key, value: outref<'Value>) =
         match store.TryGetValue(key) with
-        | true, cachedEntity ->
+        | true, entity ->
             hits.Add 1L
-            evictionProcessor.Post(EvictionQueueMessage.Update cachedEntity)
-            value <- cachedEntity.Value
+            evictionProcessor.Post(EvictionQueueMessage.Update entity)
+            value <- entity.Value
             true
         | _ ->
             misses.Add 1L
             value <- Unchecked.defaultof<'Value>
             false
 
     member _.TryAdd(key: 'Key, value: 'Value) =
-        let cachedEntity = pool.Acquire(key, value)
+        let entity = pool.Acquire(key, value)
 
-        if store.TryAdd(key, cachedEntity) then
-            evictionProcessor.Post(EvictionQueueMessage.Add cachedEntity)
-            true
+        let added = store.TryAdd(key, entity)
+
+        if added then
+            evictionProcessor.Post(EvictionQueueMessage.Add entity)
         else
-            pool.Reclaim(cachedEntity)
-            false
+            pool.Reclaim(entity)
+
+        added
 
     interface IDisposable with
         member this.Dispose() =