TTree Draw() and threadsafety with openMP

[Conor]

Hi Danilo,

Thanks for the fast response!

I was under the impression from your comment in another thread that ROOT::EnableThreadSafety() doesn’t yet work (even though 6.06 release notes indicate otherwise):

Threads in ROOT

Dear ROOT experts, I have a function that loops over TTree and draws variables, doing some stuff so it’s getting slow if the tree has large number of events. So I would like to speed it up by creating threads. So let’s say in case of 2 variables I have something like this: [color=#4000BF] std::thread t[2]; t[0] = std::thread(draw,string(argv[1]), string(argv[2]), variables[0]); t[1] = std::thread(draw,string(argv[1]), string(argv[2]), variables[1]); t[0].join(); t[1].join();[/color]…

I have been calling this and/or TThread::Initialise() already. My suspicion with the tutorial you linked to is that in my use case I am calling Draw() on a single file that is used in more than one thread. I have a dozen or so TFiles that are unique to each thread, and a single TFile that is shared across the threads. These are all only using the Draw command and are opened read-only. In the tutorial it looks like you’re acting only on unique files in each.

My use case relies on mountains of additional classes I’ve written over the years, so I’m not sure I can slim it down to a size that fits nicely in a tutorial, but I’ll have a think.