Optimise TransitEventBuffer expansion

include/quill/backend/TransitEvent.h

@@ -31,7 +31,7 @@ class LoggerBase;
 struct TransitEvent
 {
   /***/
-  TransitEvent() { formatted_msg.reserve(32); }
+  TransitEvent() = default;
 
   /***/
   ~TransitEvent() = default;
@@ -81,6 +81,9 @@ struct TransitEvent
     return (macro_metadata->log_level() != LogLevel::Dynamic) ? macro_metadata->log_level() : dynamic_log_level;
   }
 
+  /***/
+  void reserve_formatted_msg(size_t capacity = 64u) { formatted_msg.reserve(capacity); }
+
   uint64_t timestamp{0};
   MacroMetadata const* macro_metadata{nullptr};
   detail::LoggerBase* logger_base{nullptr};

include/quill/backend/TransitEventBuffer.h

@@ -28,6 +28,10 @@ class TransitEventBuffer
       _storage(std::make_unique<TransitEvent[]>(_capacity)),
       _mask(_capacity - 1u)
   {
+    for (size_t i = 0; i < _capacity; ++i)
+    {
+      _storage.get()[i].reserve_formatted_msg();
+    }
   }
 
   TransitEventBuffer(TransitEventBuffer const&) = delete;
@@ -108,13 +112,22 @@ class TransitEventBuffer
 
     auto new_storage = std::make_unique<TransitEvent[]>(new_capacity);
 
-    // Copy existing elements to the new storage
+    // Move existing elements from the old storage to the new storage.
+    // Since the buffer is full, this moves all the previous TransitEvents, preserving their order.
+    // The reader position and mask are used to handle the circular buffer's wraparound.
     size_t const current_size = size();
     for (size_t i = 0; i < current_size; ++i)
     {
       new_storage[i] = std::move(_storage[(_reader_pos + i) & _mask]);
     }
 
+    // For the new elements in the expanded buffer, reserve memory for formatted messages.
+    // This mirrors the pre-allocation done in the constructor
+    for (size_t i = current_size; i < new_capacity; ++i)
+    {
+      new_storage.get()[i].reserve_formatted_msg();
+    }
+
     _storage = std::move(new_storage);
     _capacity = new_capacity;
     _mask = _capacity - 1;