Reading events from a TFile that is being written

Newbie
1

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ROOT Version: 5.34.36
Platform: CentOS 7
Compiler: gcc 4.9

My data acquisition system writes data to ROOT files using the following code:

  fTFileHandle = TFile::Open(fOutFile,"NEW","PADME Merged Raw Events");
  if ( (!fTFileHandle) || fTFileHandle->IsZombie() ) {
    delete fTFileHandle;
    return ROOTIO_ERROR;
  }
  fTTreeMain = new TTree("RawEvents","PADME Raw Events Tree");
  fTTreeMain->Branch("RawEvent",&fTRawEvent);
...write many events to file...
  fTTreeMain->Write();
  fTFileHandle->Close();

It would be very useful for me if I could monitor the content of the events WHILE they are being written, i.e. doing something similar to the Unix command “tail -f”.

If I open the file that is being written with an external program I get some warning messages:

Warning in <TFile::Init>: file rawdata1/run_0030611_20201111_120928/run_0030611_20201111_120928_lvl1_00_006.root probably not closed, trying to recover
Info in <TFile::Recover>: rawdata1/run_0030611_20201111_120928/run_0030611_20201111_120928_lvl1_00_006.root, recovered key TTree:RawEvents at address 115620453
Warning in <TFile::Init>: successfully recovered 1 keys

I can then read the events only up to a certain point.
If I close and reopen the file I get similar warning messages and can read a bit more events.
Is there a way to open the file and keep it open while progressively reading the events shortly after they have been written to the file?

Thank you
Emanuele Leonardi

2

See an working example at: Read histogram from TFile while actively writing to it (with example) (please also note the surrounding discussions)

3

Thank you: exactly what I needed.
One final question: is there any way to switch off the warning/info messages I get when I open a file that was not closed?
E.g.

Warning in <TFile::Init>: file rawdata1/run_0030617_20201112_170343/run_0030617_20201112_170343_lvl1_00_034.root probably not closed, trying to recover
Info in <TFile::Recover>: rawdata1/run_0030617_20201112_170343/run_0030617_20201112_170343_lvl1_00_034.root, recovered key TTree:RawEvents at address 90885443
Warning in <TFile::Init>: successfully recovered 1 keys

Emanuele

4

Calling:
gErrorIgnoreLevel = kError
will reduce the printing to Error or Fatal messages.