Updated

EonaCat.LogStack.Server/Server.cs

@@ -36,7 +36,7 @@ namespace EonaCat.LogStack.Server
             _maxLogDirectorySize = maxLogDirectorySize;
         }
 
-        protected virtual Task ProcessLogAsync(string logData)
+        protected virtual async Task ProcessLogAsync(string logData)
         {
             string logsRootDirectory = "logs";
 
@@ -67,7 +67,12 @@ namespace EonaCat.LogStack.Server
             // After processing log, check directory size and clean up if needed
             CleanUpOldLogs();
 
-            return File.AppendAllTextAsync(logFilePath, logData + Environment.NewLine);
+            using (var stream = new FileStream(logFilePath, FileMode.Append, FileAccess.Write, FileShare.Read | FileShare.Delete, 4096, FileOptions.Asynchronous))
+            using (var writer = new StreamWriter(stream))
+            {
+                await writer.WriteLineAsync(logData).ConfigureAwait(false);
+                await writer.FlushAsync().ConfigureAwait(false);
+            }
         }
 
         private void CleanUpOldLogs()