logging: Add threadsafety comments

Author: MarcoFalke

src/logging.cpp

@@ -41,7 +41,7 @@ static int FileWriteStr(const std::string &str, FILE *fp)
 
 bool BCLog::Logger::StartLogging()
 {
-    std::lock_guard<std::mutex> scoped_lock(m_file_mutex);
+    std::lock_guard<std::mutex> scoped_lock(m_cs);
 
     assert(m_buffering);
     assert(m_fileout == nullptr);
@@ -216,9 +216,9 @@ std::string BCLog::Logger::LogTimestampStr(const std::string& str)
     return strStamped;
 }
 
-void BCLog::Logger::LogPrintStr(const std::string &str)
+void BCLog::Logger::LogPrintStr(const std::string& str)
 {
-    std::lock_guard<std::mutex> scoped_lock(m_file_mutex);
+    std::lock_guard<std::mutex> scoped_lock(m_cs);
     std::string str_prefixed = str;
 
     if (m_log_threadnames && m_started_new_line) {

src/logging.h

@@ -60,10 +60,10 @@ namespace BCLog {
     class Logger
     {
     private:
-        FILE* m_fileout = nullptr;
-        std::mutex m_file_mutex;
-        std::list<std::string> m_msgs_before_open;
-        bool m_buffering = true; //!< Buffer messages before logging can be started
+        mutable std::mutex m_cs;                   // Can not use Mutex from sync.h because in debug mode it would cause a deadlock when a potential deadlock was detected
+        FILE* m_fileout = nullptr;                 // GUARDED_BY(m_cs)
+        std::list<std::string> m_msgs_before_open; // GUARDED_BY(m_cs)
+        bool m_buffering{true};                    //!< Buffer messages before logging can be started. GUARDED_BY(m_cs)
 
         /**
          * m_started_new_line is a state variable that will suppress printing of
@@ -89,10 +89,14 @@ namespace BCLog {
         std::atomic<bool> m_reopen_file{false};
 
         /** Send a string to the log output */
-        void LogPrintStr(const std::string &str);
+        void LogPrintStr(const std::string& str);
 
         /** Returns whether logs will be written to any output */
-        bool Enabled() const { return m_buffering || m_print_to_console || m_print_to_file; }
+        bool Enabled() const
+        {
+            std::lock_guard<std::mutex> scoped_lock(m_cs);
+            return m_buffering || m_print_to_console || m_print_to_file;
+        }
 
         /** Start logging (and flush all buffered messages) */
         bool StartLogging();