Exclude PluginManager cache from MaxMemoryPreload monitoring

FWCore/PluginManager/src/PauseMaxMemoryPreloadSentry.cc

@@ -0,0 +1,11 @@
+#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(); }
+}  // namespace edm

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;
+  };
+}  // namespace edm
+
+#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;
     }

PerfTools/MaxMemoryPreload/README.md

@@ -16,6 +16,33 @@ LD_PRELOAD="libPerfToolsAllocMonitorPreload.so libPerfToolsMaxMemoryPreload.so"
 
 the order is important.
 
+### Pausing the monitoring
+
+It is possible to temporarily pause the monitoring by instrumenting the target application by definining the following functions
+```cpp
+// in some header,
+void pauseMaxMemoryPreload();
+void unpauseMaxMemoryPreload();
+
+// in an implementation source file
+void pauseMaxMemoryPreload() {
+}
+void unpauseMaxMemoryPreload() {
+}
+```
+and then using these in code
+```cpp
+  ...
+  pauseMaxMemoryPreload();
+  // code that should be excluded from the monitoring
+  unpauseMaxMemoryPreload();
+  ...
+```
+
+The trick is that by default these functions are defined in the application, and the functions do nothing. The `libPerfToolsMaxMemoryPreload.so` provides also the same functions that actually pause the data collection, and the LD_PRELOADing makes the application to call the functions within `libPerfToolsMaxMemoryPreload.so`.
+
+It is recommended to not pause the monitoring within a multithreaded section, because that could result in unexpected results, because the pausing setting is global.
+
 ## Reporting
 When the application ends, the monitor will report the following to standard error:
 

PerfTools/MaxMemoryPreload/src/preload.cc

@@ -26,6 +26,16 @@
 // static data member definitions
 //
 
+// Hooks the target application can be instrumented with to pause and
+// unpause the MaxMemoryPreload. Pausing the monitoring during a
+// multithreaded execution can result in unexpected results, because
+// the setting is global.
+namespace {
+  std::atomic<bool> paused = false;
+}
+void pauseMaxMemoryPreload() { paused = true; }
+void unpauseMaxMemoryPreload() { paused = false; }
+
 namespace {
   class MonitorAdaptor : public cms::perftools::AllocMonitorBase {
   public:
@@ -34,6 +44,9 @@ namespace {
 
   private:
     void allocCalled(size_t iRequested, size_t iActual, void const*) final {
+      if (paused)
+        return;
+
       nAllocations_.fetch_add(1, std::memory_order_acq_rel);
       requested_.fetch_add(iRequested, std::memory_order_acq_rel);
 
@@ -48,6 +61,9 @@ namespace {
       }
     }
     void deallocCalled(size_t iActual, void const*) final {
+      if (paused)
+        return;
+
       nDeallocations_.fetch_add(1, std::memory_order_acq_rel);
       auto present = presentActual_.load(std::memory_order_acquire);
       if (present >= iActual) {