cache pid for logging

lib/ApplicationFeatures/DaemonFeature.cpp

@@ -242,6 +242,7 @@ int DaemonFeature::forkProcess() {
 
   // child   
   LogAppender::allowStdLogging(false);
+  Logger::clearCachedPid(); 
 
   // change the file mode mask
   umask(0);

lib/Logger/Logger.cpp

@@ -67,6 +67,7 @@ bool Logger::_keepLogRotate(false);
 bool Logger::_useMicrotime(false);
 bool Logger::_showRole(false);
 char Logger::_role('\0');
+TRI_pid_t Logger::_cachedPid(0);
 std::string Logger::_outputPrefix("");
 
 std::unique_ptr<LogThread> Logger::_loggingThread(nullptr);
@@ -329,7 +330,17 @@ void Logger::log(char const* function, char const* file, int line,
   }
 
   // append the process / thread identifier
-  out << '[' << Thread::currentProcessId();
+
+  // we only determine our pid once, as currentProcessId() will
+  // likely do a syscall.
+  // this read-check-update sequence is not thread-safe, but this
+  // should not matter, as the pid value is only changed from 0 to the
+  // actual pid and never changes afterwards
+  if (_cachedPid == 0) {
+    _cachedPid = Thread::currentProcessId();
+  }
+  TRI_ASSERT(_cachedPid != 0);
+  out << '[' << _cachedPid;
 
   if (_showThreadIdentifier) {
     out << '-' << Thread::currentThreadNumber();
@@ -444,6 +455,8 @@ void Logger::shutdown() {
 
   // cleanup appenders
   LogAppender::shutdown();
+  
+  _cachedPid = 0;
 }
 
 ////////////////////////////////////////////////////////////////////////////////

lib/Logger/Logger.h

@@ -235,6 +235,9 @@ class Logger {
   static bool getUseMicrotime() {return _useMicrotime;};
   static void setKeepLogrotate(bool);
   
+  // can be called after fork()
+  static void clearCachedPid() { _cachedPid = 0; }
+
   static std::string const& translateLogLevel(LogLevel);
 
   static void log(char const* function, char const* file, int line,
@@ -275,6 +278,7 @@ class Logger {
   static bool _keepLogRotate;
   static bool _useMicrotime;
   static char _role; // current server role to log
+  static TRI_pid_t _cachedPid;
   static std::string _outputPrefix;
 
   static std::unique_ptr<LogThread> _loggingThread;