User defined logger callback implementation

Added static wsrep::log::logger_fn() method to allow user to
provide logger callback.

include/wsrep/logger.hpp

@@ -38,6 +38,12 @@ namespace wsrep
             warning,
             error
         };
+
+        /**
+         * Signature for user defined logger callback function.
+         */
+        typedef void (*logger_fn_type)(level, const char*);
+
         static const char* to_c_string(enum level level)
         {
             switch (level)
@@ -49,21 +55,36 @@ namespace wsrep
             };
             return "unknown";
         }
+
         log(enum wsrep::log::level level, const char* prefix = "")
             : level_(level)
             , prefix_(prefix)
             , oss_()
         { }
+
         ~log()
         {
-            wsrep::unique_lock<wsrep::mutex> lock(mutex_);
+            if (logger_fn_)
-            os_ << prefix_ << ": " << oss_.str() << std::endl;
+            {
+                logger_fn_(level_, oss_.str().c_str());
+            }
+            else
+            {
+                wsrep::unique_lock<wsrep::mutex> lock(mutex_);
+                os_ << prefix_ << ": " << oss_.str() << std::endl;
+            }
         }
+
         template <typename T>
         std::ostream& operator<<(const T& val)
         {
             return (oss_ << val);
         }
+
+        /**
+         * Set user defined logger callback function.
+         */
+        static void logger_fn(logger_fn_type);
     private:
         log(const log&);
         log& operator=(const log&);
@@ -72,6 +93,7 @@ namespace wsrep
         std::ostringstream oss_;
         static wsrep::mutex& mutex_;
         static std::ostream& os_;
+        static logger_fn_type logger_fn_;
     };
 
     class log_error : public log

src/logger.cpp

@@ -24,3 +24,9 @@
 std::ostream& wsrep::log::os_ = std::cout;
 static wsrep::default_mutex log_mutex_;
 wsrep::mutex& wsrep::log::mutex_ = log_mutex_;
+wsrep::log::logger_fn_type wsrep::log::logger_fn_ = 0;
+
+void wsrep::log::logger_fn(wsrep::log::logger_fn_type logger_fn)
+{
+    logger_fn_ = logger_fn;
+}

src/wsrep_provider_v26.cpp

@@ -498,20 +498,19 @@ namespace
         {
         case WSREP_LOG_FATAL:
         case WSREP_LOG_ERROR:
-            wsrep::log_error() << "wsrep-lib: " << msg;
+            wsrep::log_error() << msg;
             break;
         case WSREP_LOG_WARN:
-            wsrep::log_warning() << "wsrep-lib: " <<msg;
+            wsrep::log_warning() << msg;
             break;
         case WSREP_LOG_INFO:
-            wsrep::log_info() << "wsrep-lib: " << msg;
+            wsrep::log_info() <<  msg;
             break;
         case WSREP_LOG_DEBUG:
-            wsrep::log_debug() << "wsrep-lib: " << msg;
+            wsrep::log_debug() << msg;
             break;
         }
     }
-
 }
 
 wsrep::wsrep_provider_v26::wsrep_provider_v26(