From ec560d1fca64ec7fce8ddaba2c8eeeb67ea63cb9 Mon Sep 17 00:00:00 2001
From: Giulio Eulisse <10544+ktf@users.noreply.github.com>
Date: Wed, 15 Oct 2025 14:04:21 +0200
Subject: [PATCH] DPL Analysis: fix multiple HistogramRegistry instances per
 task

In particular when one of them needs to have its own folder.
---
 Framework/AnalysisSupport/src/AODWriterHelpers.cxx | 12 ++++++++++++
 Framework/Core/include/Framework/OutputObjHeader.h |  5 ++++-
 Framework/Core/src/HistogramRegistry.cxx           |  3 ++-
 Framework/TestWorkflows/src/o2TestHistograms.cxx   | 12 ++++++++++++
 4 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/Framework/AnalysisSupport/src/AODWriterHelpers.cxx b/Framework/AnalysisSupport/src/AODWriterHelpers.cxx
index 27dad43480913..bcf27d0be5ba3 100644
--- a/Framework/AnalysisSupport/src/AODWriterHelpers.cxx
+++ b/Framework/AnalysisSupport/src/AODWriterHelpers.cxx
@@ -339,7 +339,9 @@ AlgorithmSpec AODWriterHelpers::getOutputObjHistWriter(ConfigContext const& ctx)
         O2_SIGNPOST_END(histogram_registry, did, "deserialization", "Done deserialization.");
         // If we have a folder, we assume the first element of the path
         // to be the name of the registry.
+        bool folderForContainer = false;
         if (sourceType == HistogramRegistrySource) {
+          folderForContainer = objh->createContainer != 0;
           obj.container = objh->containerName;
         } else {
           obj.container = obj.name;
@@ -423,6 +425,16 @@ AlgorithmSpec AODWriterHelpers::getOutputObjHistWriter(ConfigContext const& ctx)
         // FIXME: handle folders
         f[route.policy]->cd("/");
         auto* currentDir = f[route.policy]->GetDirectory(currentDirectory.c_str());
+
+        // In case we need a folder for the registry, let's create it.
+        if (folderForContainer) {
+          auto* histogramRegistryFolder = currentDir->GetDirectory(obj.container.data());
+          if (!histogramRegistryFolder) {
+            histogramRegistryFolder = currentDir->mkdir(obj.container.c_str(), "", kTRUE);
+          }
+          currentDir = histogramRegistryFolder;
+        }
+
         // The name contains a path...
         int objSize = 0;
         if (sourceType == HistogramRegistrySource) {
diff --git a/Framework/Core/include/Framework/OutputObjHeader.h b/Framework/Core/include/Framework/OutputObjHeader.h
index f1c284d564f15..801642ec6af4f 100644
--- a/Framework/Core/include/Framework/OutputObjHeader.h
+++ b/Framework/Core/include/Framework/OutputObjHeader.h
@@ -37,6 +37,7 @@ enum OutputObjSourceType : unsigned int {
 /// @brief O2 header for OutputObj metadata
 struct OutputObjHeader : public BaseHeader {
   constexpr static const uint32_t sVersion = 1;
+  constexpr static const uint32_t MAX_REGISTRY_NAME_SIZE = 128;
   constexpr static const o2::header::HeaderType sHeaderType = "OutObjMD";
   constexpr static const o2::header::SerializationMethod sSerializationMethod = o2::header::gSerializationMethodNone;
   OutputObjHandlingPolicy mPolicy;
@@ -45,7 +46,9 @@ struct OutputObjHeader : public BaseHeader {
   uint16_t mPipelineIndex = 0;
   uint16_t mPipelineSize = 1;
   // Name of the actual container for the object, e.g. the HistogramRegistry name
-  char containerName[64] = {0};
+  char containerName[MAX_REGISTRY_NAME_SIZE] = {0};
+  // Wether or not the container should have a name
+  char createContainer = false;
 
   constexpr OutputObjHeader()
     : BaseHeader(sizeof(OutputObjHeader), sHeaderType, sSerializationMethod, sVersion),
diff --git a/Framework/Core/src/HistogramRegistry.cxx b/Framework/Core/src/HistogramRegistry.cxx
index 5e39fbe7181e7..9caa7cbd1f48e 100644
--- a/Framework/Core/src/HistogramRegistry.cxx
+++ b/Framework/Core/src/HistogramRegistry.cxx
@@ -55,7 +55,8 @@ OutputRef HistogramRegistry::ref(uint16_t pipelineIndex, uint16_t pipelineSize)
 {
   OutputObjHeader header{mPolicy, OutputObjSourceType::HistogramRegistrySource, mTaskHash, pipelineIndex, pipelineSize};
   // Copy the name of the registry to the haeder.
-  strncpy(header.containerName, mName.data(), 64);
+  strncpy(header.containerName, mName.data(), OutputObjHeader::MAX_REGISTRY_NAME_SIZE);
+  header.createContainer = mCreateRegistryDir ? 1 : 0;
   return OutputRef{std::string{mName}, 0, o2::header::Stack{header}};
 }
 
diff --git a/Framework/TestWorkflows/src/o2TestHistograms.cxx b/Framework/TestWorkflows/src/o2TestHistograms.cxx
index ae3610ca01e67..640a165fb91ff 100644
--- a/Framework/TestWorkflows/src/o2TestHistograms.cxx
+++ b/Framework/TestWorkflows/src/o2TestHistograms.cxx
@@ -53,6 +53,18 @@ struct EtaAndClsHistogramsSimple {
     } //
   };
 
+  HistogramRegistry registry2{
+    "registry2",
+    {
+      {"a/foo/b/eta", "#Eta", {HistType::kTH1F, {{100, -2.0, 2.0}}}},                           //
+      {"fii/c/hpt", "p_{T}", {HistType::kTH1D, {{1002, -0.01, 50.1}}}},                         //
+      {"a/foobar/phi", "#Phi", {HistType::kTH1D, {{102, 0, 2 * M_PI}}}},                        //
+      {"fifi/ptToPt", "#ptToPt", {HistType::kTH2F, {{100, -0.01, 10.01}, {100, -0.01, 10.01}}}} //
+    },
+    OutputObjHandlingPolicy::AnalysisObject,
+    false,
+    true};
+
   void init(InitContext&)
   {
     if (!trackFilterString->empty()) {