Hi Yuriy,
TNetFile supports new option "+read". This will allow you to open a
file in read mode that has already been opened in write mode by another
rootd. By default rootd does not allow readers when a file is being
written. Usefull for spying in DAQ environments, but should be used
carefully.
This change is now in CVS. You need to also update rootd.
Cheers, Fons.
On Thu, 2002-02-14 at 15:51, Yuriy Prokazov wrote:
> Dear Rene,
> thank you very much for your help. Your samples work perfectly. I
> found an interesting bug/feature of the rootd server. If I change
> in your samples TFile to TNetFile and file to
> root://server/junk.root
> where server the name of the computer with the running rootd. Write
> part works perfectly, but the read part says:
> "Error in <TNetFile::TNetFile> file already opened in write mode".
>
> When I use mounted path via nfs everything is OK. Is it possible to
> use rootd in a DAQ/Viewer way how it's shown in your examples?
>
> Best regards, Yuriy.
>
> RB> You will find below two small scripts treew.C and treer.C
> RB> Run treew.C in a Root session. This will update the file at regular
> RB> intervals.
> RB> In a separate Root session, run treer.C. This will update an histogram
> RB> reading fresh data only.
>
> RB> You can combine this example with the new producer/consumer example
> RB> in $ROOTSYS/tutorials/spyserv.C and spy.C (version 3.03 only in CVS)
>
> RB> void treew() {
> RB> TFile f("junk.root","recreate");
> RB> TNtuple *ntuple = new TNtuple("ntuple","Demo ntuple","px:py:pz:random:i");
> RB> Float_t px, py, pz;
> RB> for ( Int_t i=0; i<1000000; i++) {
> RB> gRandom->Rannor(px,py);
> RB> pz = px*px + py*py;
> RB> Float_t random = gRandom->Rndm(1);
> RB> ntuple->Fill(px,py,pz,random,i);
> RB> if (i%1000 == 1) {
> RB> ntuple->AutoSave();
> RB> f.SaveSelf();
> RB> }
> RB> }
> RB> }
>
> RB> void treer() {
> RB> TFile f("junk.root");
> RB> TCanvas c1;
> RB> Int_t first = 0;
> RB> while(1) {
> RB> f.ReadKeys();
> RB> TTree *ntuple = (TTree*)f.Get("ntuple");
> RB> if (first == 0) ntuple->Draw("px>>hpx","","",10000000,first);
> RB> else ntuple->Draw("px>>+hpx","","",10000000,first);
> RB> first = (Int_t)ntuple->GetEntries();
> RB> delete ntuple;
> RB> c1.Update();
> RB> gSystem->Sleep(1000); //sleep 1 second
> RB> }
> RB> }
>
> RB> Rene Brun
>
> RB> Yuriy Prokazov wrote:
> >>
> >> Dear ROOTers,
> >> I'd like to make work 2 independent processes where one of them
> >> writes information into the file and other reads it. If it is
> >> possible I would like to use TNetFile (if these processes are
> >> running on a different computers) or via TFile if (they are in
> >> the single box). I faced with following problem: from the WRITE
> >> process I create file using TFile and create TTree object with
> >> the single branch of a simple type. Every second WRITE process
> >> fills the branch and saves some amount of data. In the READ
> >> part I open the file using TFile::Open().
> >>
> >> The problem is that in the READ call tree->GetEntries() always
> >> returns the same number. From the ROOT source code it is
> >> obviosly clear that it could return only the one value that have
> >> been saved during initialization.
> >>
> >> But the same time file->GetFileSize() show that the file is
> >> growing.
> >>
> >> Is there any way how to make independed reading/writing and say
> >> to READ process that the file was changed and it is required to
> >> read new data?
> >>
> >> Thank you.
> >> Best regards,
> >> Yuriy.
--
Org: CERN, European Laboratory for Particle Physics.
Mail: 1211 Geneve 23, Switzerland
E-Mail: Fons.Rademakers@cern.ch Phone: +41 22 7679248
WWW: http://root.cern.ch/~rdm/ Fax: +41 22 7679480
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