[ntuple] Update chain processing tutorial

Author: enirolf

tutorials/io/ntuple/ntpl012_processor.C renamed to tutorials/io/ntuple/ntpl012_processor_chain.C

@@ -74,12 +74,14 @@ void Read(const std::vector<RNTupleOpenSpec> &ntuples)
    // Access to the entry values in this case can be achieved through RNTupleProcessor::GetEntry() or through its
    // iterator.
    auto processor = RNTupleProcessor::CreateChain(ntuples, std::move(model));
+   int prevProcessorNumber{-1};
 
    for (const auto &entry : *processor) {
       // The RNTupleProcessor provides some additional bookkeeping information. The local entry number is reset each
       // a new ntuple in the chain is opened for processing.
-      if (processor->GetLocalEntryNumber() == 0) {
-         std::cout << "Processing " << ntuples.at(processor->GetCurrentNTupleNumber()).fNTupleName << " ("
+      if (static_cast<int>(processor->GetCurrentProcessorNumber()) > prevProcessorNumber) {
+         prevProcessorNumber = processor->GetCurrentProcessorNumber();
+         std::cout << "Processing " << ntuples.at(prevProcessorNumber).fNTupleName << " ("
                    << processor->GetNEntriesProcessed() << " total entries processed so far)" << std::endl;
       }
 
@@ -93,7 +95,7 @@ void Read(const std::vector<RNTupleOpenSpec> &ntuples)
    hPx.DrawCopy();
 }
 
-void ntpl012_processor()
+void ntpl012_processor_chain()
 {
    // The ntuples to generate and subsequently process. The model of the first ntuple will be used to construct the
    // entry used by the processor.