For our experiment multiple devices are read out every 100 ms, their data is transferred to some buffers and these are then filled into a TTree, at the moment a couple of thousand Double_t per event. This TTree is then saved to a TFile, which is read in different instances for online and offline ana…

Hi Anno, @pcanal can correct me if I’m wrong, but I don’t think reading a TTree in a process while it’s being written in another process is supported. You might be able to make it work, but by design some information is written in the TTree footer when writing is done, and that will be missing if y…

[image] eguiraud: but I don’t think reading a TTree in a process while it’s being written in another process is supported. It is. See the thread Wile’s forward for example.

Ok yes it’s possible but you might run in a bunch of weird effects, especially if you don’t lock writing while reading :+1:

Home | News | Documentation | Download

ROOT Forum

Saving a TTree to a TFile every 100 ms

Newbie

tree

Wile_E_Coyote June 15, 2021, 1:44pm 3

Errors in remote client reading of TTree from TFile via xrootd while simultaneously updating TTree on server ROOT

Reading from a TFile is that is being written to is supported to some extent. //////////////////////////////////////////////////////////////////////////////// /// Read the linked list of keys. /// /// Every directory has a linked list (fKeys). This linked list has been /// written on the file via WriteKeys as a single data record. /// /// It is interesting to call this function in the following situation. /// Assume another process1 is connecting this directory in Update mode /// - Process1 i…

Read histogram from TFile while actively writing to it (with example) ROOT

@pcanal : I determined the cause of the segfault was calling Draw() on the TH1I pointer that was still NULL. I realize now my issue with delete file->FindObject(name); file->ReadKeys(); These commands only work if you have loaded the ROOT file that is actively being written. This does not work if you have opened an old file of the same name. When the file is RECREATEd, I now have two working methods of reading a file from disk while a process is actively writing to it. Below…

TTree and Thread compatibility ROOT

See an example in the two files fw.C and fr.C in attachment. Although not using threads you should be able to pick the idea. Rene fr.C (845 Bytes) fw.C (1.83 KB)

show post in topic

Home
Categories
Guidelines
Terms of Service
Privacy Policy

Powered by Discourse, best viewed with JavaScript enabled