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cms-sw / cmssw

CMS Offline Software
http://cms-sw.github.io/
Apache License 2.0
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ROOT TDirectory IO in CMSSW #27447

Open schneiml opened 5 years ago

schneiml commented 5 years ago

Dear framework experts,

Within the DQMStore, we have the functionality to write the classic TDirectory based output file. This needs to be preserved, since many (if not most) DQM-based tools consume DQM data in this format. Currently, we write this format at the end of production HARVESTING jobs, and in many less-mainstream workflows.

The existing code uses gDirectory and all the usual ROOT things in the classic ways [1], which as I understand is not threadsafe (or maybe it is, setting the correct options in ROOT?).

Now I wonder if the new saving code can reuse the old logic, or if we should use the occasion to do this in some more modern way [2]. Actually, I am not sure if there even is a better way. Any advice?

The old save API (where any module can call save on the DQMStore at any time to write a ROOT file) probably needs to be preserved (a number of niche workflows depend on that), but the main use case in HARVESTING might be possible to turn into a proper output module.

[1] https://github.com/cms-sw/cmssw/blob/master/DQMServices/Core/src/DQMStore.cc#L2633-L2668 [2] I do plan to gt rid of the lat:: dependencies, at least...

cmsbuild commented 5 years ago

A new Issue was created by @schneiml Marcel Schneider.

@davidlange6, @Dr15Jones, @smuzaffar, @fabiocos, @kpedro88 can you please review it and eventually sign/assign? Thanks.

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