PROOF. Can the slaves share a common object?

[atd]

Hello

As far as I know, in a parallel proof session, the slaves of the selector copy the objects; and they are merged at the end.

I would like to process the entries in parallel, store part of the processed information in a std::map, and at the end (1 thread) work with the map.

So, I can imagine two ways of doing it:
-Share a unique std::map (protected by a mutex)
-Each slave fill a map, and merged them at the end. This could be time consuming, but the size of the map would be small (around several million of elements).

Question: is any of the options possible, or should I use std::thread?

Thank you for your time.

Regards,
atd

[amvargash]

You should write your TSelector and make global the variables that you want to use (for instance creating them in the header file).

From the docs:

void MySelector::SlaveBegin(TTree *tree) {
   // SlaveBegin() is a good place to create histograms.
   // For PROOF, this is called for each worker.
   // The TTree* is there for backward compatibility; e.g. PROOF passes 0.

  // fOutput is inherited from TSelector. Make sure you ::Add the objects
  // which will be used in different methods of the class (specially in Terminate).

Bool_t MySelector::Process(Long64_t entry) {
   // The Process() function is called for each entry in the tree to be
   // processed. The entry argument specifies which entry in the currently
   // loaded tree is to be processed.
   // It can be passed to either EventSelector::GetEntry() or TBranch::GetEntry()
   // to read either all or the required parts of the TTree.
   //
   // This function should contain the "body" of the analysis: select relevant
   // tree entries, run algorithms on the tree entry and typically fill histograms.

void MySelector::Terminate() {
   // The Terminate() function is the last function to be called during the
   // analysis of a tree with a selector. It always runs on the client, it can
   // be used to present the results graphically or save the results to file.

Hope this helps,

[atd]

Hello

I would like a container to be filled by different slaves, and at the end have only one container. Is it possible? (I think that a global container will be filled independently by the different slaves).

Thank you for your time.

Regards.