Improvement to DerivationFramework::PrescaleTool to give reproducible results when running in MP/MT

ATLASG-1450

It was noted that the derivation framework PrescaleTool is not safe in a multi-process/thread environment due to its use of an event counter, such that the order of execution needs to be the same to get reproducible results. This MR changes the tool to use the event number rather than a counter, and since the event number is independent of the the order of processing, the outcome of the prescaler is now exactly reproducible and predictable.


Former-commit-id: 34bb2bdbc7f28e74a954c5952ce0a7efb2fafc9b

PhysicsAnalysis/DerivationFramework/DerivationFrameworkTools/CMakeLists.txt

@@ -14,6 +14,7 @@ atlas_depends_on_subdirs(
    PhysicsAnalysis/AnalysisCommon/PATCore
    PhysicsAnalysis/DerivationFramework/DerivationFrameworkInterfaces
    Trigger/TrigAnalysis/TrigDecisionTool
+   Event/xAOD/xAODEventInfo
    PRIVATE
    Control/AthenaKernel
    PhysicsAnalysis/CommonTools/ExpressionEvaluation )
@@ -26,7 +27,7 @@ atlas_add_library( DerivationFrameworkToolsLib
    DerivationFrameworkTools/*.h src/*.cxx
    PUBLIC_HEADERS DerivationFrameworkTools
    PRIVATE_INCLUDE_DIRS ${ROOT_INCLUDE_DIRS}
-   LINK_LIBRARIES AthenaBaseComps xAODBase GaudiKernel PATCoreLib
+   LINK_LIBRARIES AthenaBaseComps xAODBase GaudiKernel PATCoreLib xAODEventInfo
    TrigDecisionToolLib ExpressionEvaluationLib DerivationFrameworkInterfacesLib
    PRIVATE_LINK_LIBRARIES ${ROOT_LIBRARIES} AthenaKernel )
 

PhysicsAnalysis/DerivationFramework/DerivationFrameworkTools/DerivationFrameworkTools/PrescaleTool.h

@@ -25,7 +25,7 @@ namespace DerivationFramework {
       virtual bool eventPassesFilter() const;
 
     private:
-      mutable int m_prescale, m_eventCounter;	
+      unsigned int m_prescale;	
   }; 
 }
 

PhysicsAnalysis/DerivationFramework/DerivationFrameworkTools/src/PrescaleTool.cxx

@@ -11,6 +11,7 @@
 // Use of ExpressionParsing to analyse a more complex string
 
 #include "DerivationFrameworkTools/PrescaleTool.h"
+#include "xAODEventInfo/EventInfo.h"
 
 namespace DerivationFramework {
 
@@ -30,7 +31,6 @@ namespace DerivationFramework {
       ATH_MSG_FATAL("Prescale of less than 1 makes no sense");
       return StatusCode::FAILURE;
     }
-    m_eventCounter = 0;
     return StatusCode::SUCCESS;
   }
 
@@ -41,9 +41,11 @@ namespace DerivationFramework {
 
   bool PrescaleTool::eventPassesFilter() const
   {
+    const xAOD::EventInfo* ei = 0;
+    CHECK( evtStore()->retrieve( ei , "EventInfo" ) );
+    uint32_t eventNumber ei->eventNumber(); 
     bool accept(false);
-    if (m_eventCounter % m_prescale == 0) accept = true;
-    ++m_eventCounter; 
+    if (eventNumber % m_prescale == 0) accept = true;
     return accept;
   }