fix: run the commit handler on a dedicated background thread

CHANGELOG.md

@@ -5,6 +5,7 @@
 * FIXED: Retry JSON parse on read to tolerate concurrent partial-file writes
 * FIXED: A failing commit action no longer hangs other callers in the same batch
 * FIXED: Collection key in file not matching configured case is now matched case-insensitively, instead of reading empty and duplicating the key on save
+* FIXED: Run DataStore's commit handler on its own background thread, so writes are not delayed when the application's thread pool is busy
 
 ### [2.4.2] - 2023-06-25
 * FIXED: Duplicate collection data to JSON on save when configured case was not used with collection name

JsonFlatFileDataStore/DataStore.cs

@@ -72,23 +72,39 @@ public DataStore(string path, bool useLowerCamelCase = true, string keyProperty
 
         _jsonData = GetJsonObjectFromFile();
 
-        // Run updates on a background thread and use BlockingCollection to prevent multiple updates to run simultaneously
-        Task.Run(() =>
+        // Run updates on a dedicated background thread and use BlockingCollection to prevent multiple updates to run simultaneously.
+        // The handler blocks on Take() for the whole lifetime of the store, so it must not sit on a thread pool thread: a process
+        // holding several stores would then permanently occupy that many pool threads and starve every other continuation.
+        var commitHandlerThread = new Thread(() =>
         {
-            CommitActionHandler.HandleStoreCommitActions(_cts.Token,
-                _updates,
-                executionState => _executingJsonUpdate = executionState,
-                jsonText =>
-                {
-                    lock (_jsonData)
+            try
+            {
+                CommitActionHandler.HandleStoreCommitActions(_cts.Token,
+                    _updates,
+                    executionState => _executingJsonUpdate = executionState,
+                    jsonText =>
                     {
-                        _jsonData = JObject.Parse(jsonText);
-                    }
+                        lock (_jsonData)
+                        {
+                            _jsonData = JObject.Parse(jsonText);
+                        }
+
+                        return FileAccess.WriteJsonToFile(_filePath, _encryptJson, jsonText);
+                    },
+                    GetJsonTextFromFile);
+            }
+            catch
+            {
+                // Keeps the previous Task.Run semantics, where an exception escaping the handler
+                // ended the loop as an unobserved task exception instead of tearing down the process.
+            }
+        })
+        {
+            IsBackground = true,
+            Name = "JsonFlatFileDataStore commit handler"
+        };
 
-                    return FileAccess.WriteJsonToFile(_filePath, _encryptJson, jsonText);
-                },
-                GetJsonTextFromFile);
-        });
+        commitHandlerThread.Start();
     }
 
     public void Dispose()