LumiblockHistogramProvider.h

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/
 
#ifndef AthenaMonitoringKernel_HistogramFiller_LumiblockHistogramProvider_h
#define AthenaMonitoringKernel_HistogramFiller_LumiblockHistogramProvider_h
 
#include <map>
#include <memory>
#include <utility>
 
#include "AthenaMonitoringKernel/GenericMonitoringTool.h"
#include "AthenaMonitoringKernel/HistogramDef.h"
#include "AthenaMonitoringKernel/IHistogramProvider.h"
 
#include "HistogramFactory.h"
 
namespace Monitored {
  class LumiblockHistogramProvider : public IHistogramProvider {
  public:
    LumiblockHistogramProvider(GenericMonitoringTool* const gmTool,
        std::shared_ptr<HistogramFactory> factory,
        const HistogramDef& histDef)
      : IHistogramProvider()
      , m_gmTool(gmTool)
      , m_factory(std::move(factory))
      , m_histDef(histDef)
      {}

    TNamed* histogram() override {
 
      const unsigned lumiBlock = m_gmTool->lumiBlock();
      std::scoped_lock lock(m_mutex);  // access to m_hists
 
      /* Find existing histogram. In the unlikely case of a very old lumiblock
         being processed, it would be filled into the oldest histogram. */
      const auto it = m_hists.lower_bound(lumiBlock);
      if (it!=m_hists.end() && it->second.second!=nullptr) {
        return it->second.second;
      }
 
      if (m_histDef.kLBNHistoryDepth <= 0) {
        throw HistogramException("Histogram >"+ m_histDef.path + "< has invalid kLBNHistoryDepth.");
      }
 
      const int historyDepth = m_histDef.kLBNHistoryDepth;
      const unsigned lumiPage = lumiBlock/historyDepth;
 
      // Helpers to calculate min/max lumiblock for a given "page" (histogram)
      auto minLumiBlock = [=](unsigned lumiPage) { return lumiPage * historyDepth; };
      auto maxLumiBlock = [=](unsigned lumiPage) { return (lumiPage+1) * historyDepth - 1; };
 
      // create new histogram definition with updated alias
      HistogramDef def = m_histDef;
      def.alias += "_LB" + std::to_string(minLumiBlock(lumiPage));
      if (historyDepth > 1) {
        def.alias += "_" + std::to_string(maxLumiBlock(lumiPage));
      }
 
      TNamed* hist = m_factory->create(def);
      m_hists.emplace(maxLumiBlock(lumiPage), std::make_pair(std::move(def), hist));
 
      // deregister old histograms
      for (auto it = m_hists.begin(); it!=m_hists.end();) {
        const unsigned maxLB = it->first;
        if (maxLB + s_deregDelay <= lumiBlock) {
          m_factory->remove(it->second.first);
          it = m_hists.erase(it);  // this advances iterator by one
        }
        else break;  // don't need to search further as std::map is sorted
      }
 
      return hist;
    }
 
  private:
    GenericMonitoringTool* const m_gmTool;
    std::shared_ptr<HistogramFactory> m_factory;
    const HistogramDef m_histDef;

    static const unsigned s_deregDelay{5};

    std::map<unsigned, std::pair<HistogramDef, TNamed*>> m_hists;
    std::mutex m_mutex;  
  };
}
 
#endif /* AthenaMonitoringKernel_HistogramFiller_LumiblockHistogramProvider_h */