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

@@ -263,16 +263,13 @@ bool ProcStats::fetch( procInfo& f ) {
 
 #if defined( __linux__ ) or defined( __APPLE__ )
 
-  linux_proc pinfo;
-
   auto read_proc = [&]() {
-    int  cnt{0};
-    char buf[500];
+    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(
@@ -292,19 +289,14 @@ bool ProcStats::fetch( procInfo& f ) {
       const auto pr_rssize = static_cast<double>( pinfo.rss );
       f.vsize              = pr_size / ( 1024 * 1024 );
       f.rss                = pr_rssize * m_pg_size / ( 1024 * 1024 );
+      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; }
   }