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description: GSI Helmholtzzentrum für Schwerionenforschung
items: How to create more than one output event in FairTask Exec()-function?
items: Re: How to create more than one output event in FairTask Exec()-function?

How to create more than one output event in FairTask Exec()-function?
type: item
description: Dear all, I would like to design an R3BRoot FairTask that merges several .root-files. So suppose that I create a TClonesArray* fOutput; that I write its content with FairRootManaber::Register to an output-file, and that I expand the fOutput-array with one object at a time using the new-operator (inside the Exec()-function), is there a way to manually call a command for writing fOutput to the file and emptying it halfway inside the Exec()-function? So that I essentially generate multiple events in the output-tree for a single Exec()-call? Many thanks in advance! Christiaan Douma.
creator: C. A. Douma
date: 2019-03-26T11:41:36-00:00

Re: How to create more than one output event in FairTask Exec()-function?
type: item
description: Hello, what is it you actually want to accomplish? What should be "merged" and why? Quote: is there a way to manually call a command for writing fOutput to the file and emptying it halfway inside the Exec()-function? So that I essentially generate multiple events in the output-tree for a single Exec()-call? I do not think it is a good Idea to work against one of the main principles of the data processing system. In- and Output files should have a 1:1 relationship - so one can use data from several root files together and be sure its the correct event each time (see 14.16.2 https://root.cern.ch/root/htmldoc/guides/users-guide/Trees.html#example- 3-adding-friends-to-trees). I suspect your problem is somewhere else, and can be solved differently. Jan
creator: Jan Mayer
date: 2019-03-27T09:34:57-00:00

Re: How to create more than one output event in FairTask Exec()-function?
type: item
description: Dear Jan, The ultimate goal of this exercise is to do my simulations in multi-thread mode. To avoid the complicated C++ multithread programming, my thoughts went to using a bash-script for running, say, 4 copies of r3b_sim.C in parallel (in different shells). Then, I can run your digitizer afterwards (also 4x in different shells). However, this will then produce 4 distinct .root-files, all with their own digitizer output tree. Hence, I wanted to write another FairTask that does nothing more then merging these 4 files into one. But since FairTask runs Exec() ones per event and reads & writes one event at a time, taking event 1 from 4 different files & writing them as event 1,2,3,4 does not seem possible withing Exec(). Hence my question: can I manually call a write & reset function for the output TClonesArray? In that Case, I can use AddFriend() on the 4 digitizer files, read one event from each file during one Exec()-call and then call the write & reset function 4 times to produce 4 output events within that same Exec()-call. Christiaan.
creator: C. A. Douma
date: 2019-03-27T11:32:36-00:00

Re: How to create more than one output event in FairTask Exec()-function?
type: item
description: Quote: This will then produce 4 distinct .root-files, all with their own digitizer output tree. Hence, I wanted to write another FairTask that does nothing more then merging these 4 files into one. Aha! Now we're talking. Quote: Hence my question: can I manually call a write & reset function for the output TClonesArray? You don't need to do that. At all. I mean, if you think about it, this must be such a common problem! Everyone would face that at some point, right? Even the experimental data is split into multiple files automatically. Since decades, people would have to work with that, right? Having their code run over terabytes of data in hundreds of root files! There are two main solutions: Add the file contents together to form a new large file with "hadd" (not recommended), or simply tell ROOT that the input is split over multiple files - in ROOT terms, that is called a "TChain". The FairRoot equivalent / abstraction is in "FairFileSource", which has a function "AddFile", which does what it says. /**Add ROOT file to input, the file will be chained to already added files*/ void AddFile(TString FileName);
creator: Jan Mayer
date: 2019-03-27T12:16:01-00:00

Re: How to create more than one output event in FairTask Exec()-function?
type: item
description: FairFileSource::AddFile() looks promising. How can I use it? In a steering macro, I do FairRunAna* run = new FairRunAna(); run->SetInputFile("<path to>/DigiFile.root"); Can I then just do run->AddFile("<path to>/DigiFile_2.root"); and do run->Run(0,twice as many events as in a single file); Christiaan.
creator: C. A. Douma
date: 2019-03-27T13:16:02-00:00

Re: How to create more than one output event in FairTask Exec()-function?
type: item
description: auto source = new FairFileSource("<path to>/DigiFile.root"); source->AddFile("<path to>/DigiFile_2.root"); auto run = new FairRunAna(); run->SetSource(source); "SetInputFile" is deprecated anyway. Also, with run->Run(0, 0); all available events will be processed. No need to specifying the exact number.
creator: Jan Mayer
date: 2019-03-27T13:27:26-00:00

Re: How to create more than one output event in FairTask Exec()-function?
type: item
description: Thank you. I will try it. Christiaan.
creator: C. A. Douma
date: 2019-03-27T14:35:39-00:00