feat: Add logging of dropped messages

include/spdlog/async_logger-inl.h

@@ -7,6 +7,7 @@
 #    include <spdlog/async_logger.h>
 #endif
 
+#include <spdlog/spdlog.h>
 #include <spdlog/sinks/sink.h>
 #include <spdlog/details/thread_pool.h>
 
@@ -66,6 +67,15 @@ SPDLOG_INLINE void spdlog::async_logger::backend_sink_it_(const details::log_msg
         }
     }
 
+    if (auto pool_ptr = thread_pool_.lock())
+    {
+        auto lost_messages = pool_ptr->overrun_counter();
+        if (lost_messages > 0) {
+            spdlog::warn("Lost {} messages.", lost_messages);
+            pool_ptr->reset_overrun_counter();
+        }
+    }
+
     if (should_flush_(msg))
     {
         backend_flush_();