Pause MaxMemoryPreload for edmplugincache file reading in PluginManager

In a local developer area with many packages checked out, the
PluginManager cache can be tens of megabytes larger than in a
developer area without packages being checked out. This difference can
result in false positive warnings in MaxMemoryPreload monitoring in PR
tests. An easy way (even if hacky) out is to exclude the PluginManager
cache from the MaxMemoryPreload monitoring.

FWCore/PluginManager/src/PauseMaxMemoryPreloadSentry.cc

@@ -0,0 +1,16 @@
+#include "PauseMaxMemoryPreloadSentry.h"
+
+// By default do nothing, but add "hooks" that MaxMemoryPreload can
+// override with LD_PRELOAD
+void pauseMaxMemoryPreload() {}
+void unpauseMaxMemoryPreload() {}
+
+namespace edm {
+  PauseMaxMemoryPreloadSentry::PauseMaxMemoryPreloadSentry() {
+    pauseMaxMemoryPreload();
+  }
+  PauseMaxMemoryPreloadSentry::~PauseMaxMemoryPreloadSentry(){
+    unpauseMaxMemoryPreload();
+  }
+}
+

FWCore/PluginManager/src/PauseMaxMemoryPreloadSentry.h

@@ -0,0 +1,17 @@
+#ifndef FWCore_PluginManager_src_PauseMaxMemoryPreloadSentry_h
+#define FWCore_PluginManager_src_PauseMaxMemoryPreloadSentry_h
+
+namespace edm {
+  class PauseMaxMemoryPreloadSentry {
+  public:
+    PauseMaxMemoryPreloadSentry();
+    ~PauseMaxMemoryPreloadSentry();
+
+    PauseMaxMemoryPreloadSentry(const PauseMaxMemoryPreloadSentry&) = delete;
+    PauseMaxMemoryPreloadSentry(PauseMaxMemoryPreloadSentry&&) = delete;
+    PauseMaxMemoryPreloadSentry& operator=(const PauseMaxMemoryPreloadSentry&) = delete;
+    PauseMaxMemoryPreloadSentry& operator=(PauseMaxMemoryPreloadSentry&&) = delete;
+  };
+}
+
+#endif

FWCore/PluginManager/src/PluginManager.cc

@@ -29,6 +29,8 @@
 #include "FWCore/Utilities/interface/Exception.h"
 #include "FWCore/Utilities/interface/thread_safety_macros.h"
 
+#include "PauseMaxMemoryPreloadSentry.h"
+
 namespace edmplugin {
   //
   // constants, enums and typedefs
@@ -47,6 +49,7 @@ namespace edmplugin {
         throw cms::Exception("PluginMangerCacheProblem")
             << "Unable to open the cache file '" << cacheFile.string() << "'. Please check permissions on file";
       }
+      edm::PauseMaxMemoryPreloadSentry pauseSentry;;
       CacheParser::read(file, dir, categoryToInfos);
       return true;
     }