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{-1};
+  int                pid{ -1 };
   char               comm[400];
   char               state;
-  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};
+  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__
 
@@ -259,21 +259,17 @@ 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};
-  linux_proc pinfo;
-  int        cnt{0};
-  char       buf[500];
-
   auto read_proc = [&]() {
+    bool       ok = true;
+    int        cnt{ 0 };
+    char       buf[500];
+    linux_proc pinfo;
     m_ufd.lseek( 0, SEEK_SET );
-    if ( ( cnt = m_ufd.read( buf, sizeof( buf ) ) ) < 0 ) {
-      std::cerr << "ProcStats : LINUX Read of Proc file failed:" << std::endl;
-      return false;
-    }
+    if ( ( cnt = m_ufd.read( buf, sizeof( buf ) ) ) < 0 ) { ok = false; }
     if ( cnt > 0 ) {
       buf[std::min( static_cast<std::size_t>( cnt ), sizeof( buf ) - 1 )] = '\0';
       sscanf(
@@ -289,23 +285,19 @@ bool ProcStats::fetch( procInfo& f ) {
           &pinfo.kstkesp, &pinfo.kstkeip, &pinfo.signal, &pinfo.blocked, &pinfo.sigignore, &pinfo.sigcatch,
           &pinfo.wchan );
       // resident set size in pages
-      pr_size   = (double)pinfo.vsize;
-      pr_rssize = (double)pinfo.rss;
-      f.vsize   = pr_size / ( 1024 * 1024 );
-      f.rss     = pr_rssize * m_pg_size / ( 1024 * 1024 );
+      const auto       pr_size   = static_cast<double>( pinfo.vsize );
+      const auto       pr_rssize = static_cast<double>( pinfo.rss );
+      constexpr double MB        = 1.0 / ( 1024 * 1024 );
+      f.vsize                    = pr_size * MB;
+      f.rss                      = pr_rssize * m_pg_size * MB;
+      if ( 0 == pinfo.vsize ) { ok = false; }
     }
-    return true;
+    return ok;
   };
 
   // attempt to read from proc
   if ( !read_proc() ) {
-    std::cerr << "ProcStats : -> Will try reopening process proc stats" << std::endl;
-    open_ufd();
-    if ( !read_proc() ) { return false; }
-  }
-
-  if ( 0 == pinfo.vsize ) {
-    std::cerr << "ProcStats : 0==vsize -> Will try reopening process proc stats" << std::endl;
+    std::cerr << "ProcStats : -> Problems reading proc file. Will try reopening..." << std::endl;
     open_ufd();
     if ( !read_proc() ) { return false; }
   }