this session will include discussions on:

• migrating serial Algs to cloneable Algs
• writing re-entrant Algs
• sharing data between clones
  • explicit sharing vs merging at finalize
• I also want some feedback on how we should deal with Histograms in cloned Algs
  • each clone gets its own hist? how to merge?
  • clones share a hist, and do locking themselves?
  • clones share a hist, and the THistSvc manages the locking?
• PROPOSAL:
  • default behaviour of THistSvc is each clone gets it's own copy. histograms in clones are moved to memory resident. primary algorithm must explicitly call THistSvc->merge(id) during finalize to have cloned histograms merged into it
  • new method THistSvc::regSharedHist, which will create a shared instance of the Histogram for all clones
    • during execute, clients MUST lock histogram before manipulating it:
    • auto lockGuard = THistSvc->getLock(hist);
    • unlocked automatically when goes out of scope

Tomasz: we have to sum more frequently online i.e. before every publication
and TDAQ has implementation for it:
https://svnweb.cern.ch/trac/atlastdaq/browser/DAQ/DataFlow/histmon/trunk/src/THistRegisterImpl.cxx#L288