Merge pull request #1918 from matt77hias/v1.x

Made mutex member variable mutable

include/spdlog/details/backtracer.h

@@ -42,4 +42,5 @@ public:
 
 #ifdef SPDLOG_HEADER_ONLY
 #include "backtracer-inl.h"
-#endif
+#endif
+

include/spdlog/details/synchronous_factory.h

@@ -21,4 +21,5 @@ struct synchronous_factory
         return new_logger;
     }
 };
-} // namespace spdlog
+} // namespace spdlog
+

include/spdlog/fmt/fmt.h

@@ -24,4 +24,5 @@
 #else // SPDLOG_FMT_EXTERNAL is defined - use external fmtlib
 #include <fmt/core.h>
 #include <fmt/format.h>
-#endif
+#endif
+

include/spdlog/sinks/base_sink.h

@@ -37,7 +37,7 @@ public:
 protected:
     // sink formatter
     std::unique_ptr<spdlog::formatter> formatter_;
-    Mutex mutex_;
+    mutable Mutex mutex_;
 
     virtual void sink_it_(const details::log_msg &msg) = 0;
     virtual void flush_() = 0;

include/spdlog/sinks/basic_file_sink.h

@@ -55,4 +55,5 @@ inline std::shared_ptr<logger> basic_logger_st(const std::string &logger_name, c
 
 #ifdef SPDLOG_HEADER_ONLY
 #include "basic_file_sink-inl.h"
-#endif
+#endif
+