ProcStats : Use mutex lock to make fetch() thread safe.

Whilst investigating a possible memory issue using the Memory Auditor, I discovered the information printed was garbled if multiple threads where used.

The issue was the ProcStats::fetch method which was not thread safe. This MR fixes that with a simple mutex lock.

I also did a drive-by cleanup and code modernisation.

FYI @clemenci

GaudiAud/src/ProcStats.cpp

@@ -198,41 +198,41 @@
              (divide by sysconf(_SC_CLK_TCK).
 */
 struct linux_proc {
-  int                pid;
+  int                pid{-1};
   char               comm[400];
   char               state;
-  int                ppid;
-  int                pgrp;
-  int                session;
-  int                tty;
-  int                tpgid;
-  unsigned long      flags;
-  unsigned long      minflt;
-  unsigned long      cminflt;
-  unsigned long      majflt;
-  unsigned long      cmajflt;
-  unsigned long      utime;
-  unsigned long      stime;
-  long               cutime;
-  long               cstime;
-  long               priority;
-  long               nice;
-  long               num_threads;
-  long               itrealvalue;
-  unsigned long long starttime;
-  unsigned long      vsize;
-  long               rss;
-  unsigned long      rlim;
-  unsigned long      startcode;
-  unsigned long      endcode;
-  unsigned long      startstack;
-  unsigned long      kstkesp;
-  unsigned long      kstkeip;
-  unsigned long      signal;
-  unsigned long      blocked;
-  unsigned long      sigignore;
-  unsigned long      sigcatch;
-  unsigned long      wchan;
+  int                ppid{-1};
+  int                pgrp{-1};
+  int                session{-1};
+  int                tty{-1};
+  int                tpgid{-1};
+  unsigned long      flags{0};
+  unsigned long      minflt{0};
+  unsigned long      cminflt{0};
+  unsigned long      majflt{0};
+  unsigned long      cmajflt{0};
+  unsigned long      utime{0};
+  unsigned long      stime{0};
+  long               cutime{0};
+  long               cstime{0};
+  long               priority{0};
+  long               nice{0};
+  long               num_threads{0};
+  long               itrealvalue{0};
+  unsigned long long starttime{0};
+  unsigned long      vsize{0};
+  long               rss{0};
+  unsigned long      rlim{0};
+  unsigned long      startcode{0};
+  unsigned long      endcode{0};
+  unsigned long      startstack{0};
+  unsigned long      kstkesp{0};
+  unsigned long      kstkeip{0};
+  unsigned long      signal{0};
+  unsigned long      blocked{0};
+  unsigned long      sigignore{0};
+  unsigned long      sigcatch{0};
+  unsigned long      wchan{0};
 };
 #endif // __linux__ or __APPLE__
 
@@ -259,13 +259,13 @@ void ProcStats::open_ufd() {
 bool ProcStats::fetch( procInfo& f ) {
   if ( !m_valid ) { return false; }
 
-  std::scoped_lock lock{ m_mutex };
+  std::scoped_lock lock{m_mutex};
 
 #if defined( __linux__ ) or defined( __APPLE__ )
 
-  double     pr_size{ 0 }, pr_rssize{ 0 };
+  double     pr_size{0}, pr_rssize{0};
   linux_proc pinfo;
-  int        cnt{ 0 };
+  int        cnt{0};
   char       buf[500];
 
   m_ufd.lseek( 0, SEEK_SET );