From 245c41a8925b79262cab460c9eaf1c1456858b82 Mon Sep 17 00:00:00 2001
From: Wouter Deconinck <wdconinc@gmail.com>
Date: Tue, 28 Oct 2025 18:57:37 -0500
Subject: [PATCH 1/2] refactor: use std::map for deterministic ordering in
 SimCalorimeterHitProcessor

---
 src/algorithms/calorimetry/SimCalorimeterHitProcessor.cc | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/algorithms/calorimetry/SimCalorimeterHitProcessor.cc b/src/algorithms/calorimetry/SimCalorimeterHitProcessor.cc
index ca295a51b7..81c1745599 100644
--- a/src/algorithms/calorimetry/SimCalorimeterHitProcessor.cc
+++ b/src/algorithms/calorimetry/SimCalorimeterHitProcessor.cc
@@ -23,6 +23,7 @@
 #include <stdexcept>
 #include <tuple>
 #include <unordered_map>
+#include <map>
 #include <variant>
 #include <vector>
 
@@ -166,8 +167,10 @@ void SimCalorimeterHitProcessor::process(const SimCalorimeterHitProcessor::Input
   auto [out_hits, out_hit_contribs] = output;
 
   // Map for staging output information. We have 2 levels of structure:
-  //   - top level: (MCParticle, Merged Hit CellID)
+  //   - top level: (MCParticle, Merged Hit CellID, TimeID)
   //   - second level: (Merged Contributions)
+  // We use std::map instead of std::unordered_map to ensure deterministic ordering
+  // and reproducible results between single-threaded and multi-threaded execution.
   // Ideally we would want immediately create our output objects and modify the
   // contributions when needed. That could reduce the following code to a single loop
   // (instead of 2 consecutive loops). However, this is not possible as we may have to merge
@@ -175,9 +178,7 @@ void SimCalorimeterHitProcessor::process(const SimCalorimeterHitProcessor::Input
   // reasonable contribution merging, at least the intermediary structure should be
   // quite a bit smaller than the original hit collection.
   using HitIndex = std::tuple<edm4hep::MCParticle, uint64_t /* cellID */, int /* timeID */>;
-  std::unordered_map<HitIndex,
-                     std::unordered_map<uint64_t /* cellID */, HitContributionAccumulator>>
-      hit_map;
+  std::map<HitIndex, std::map<uint64_t /* cellID */, HitContributionAccumulator>> hit_map;
 
   for (const auto& ih : *in_hits) {
     // the cell ID of the new superhit we are making

From 72891b8b63b3b70758629d9cf23251c95508c181 Mon Sep 17 00:00:00 2001
From: Wouter Deconinck <wdconinc@gmail.com>
Date: Tue, 28 Oct 2025 19:15:16 -0500
Subject: [PATCH 2/2] refactor: use std::map for deterministic ordering in
 SimCalorimeterHitProcessor (fix: iwyu) (#2162)

This PR applies the include-what-you-use fixes as suggested by
https://github.com/eic/EICrecon/actions/runs/18892744942.
Please merge this PR into the branch `SimCalorimeterHitProcessor-map`
to resolve failures in PR #2161.

Auto-generated by [create-pull-request][1]

[1]: https://github.com/peter-evans/create-pull-request

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
---
 src/algorithms/calorimetry/SimCalorimeterHitProcessor.cc | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/algorithms/calorimetry/SimCalorimeterHitProcessor.cc b/src/algorithms/calorimetry/SimCalorimeterHitProcessor.cc
index 81c1745599..524f2d9593 100644
--- a/src/algorithms/calorimetry/SimCalorimeterHitProcessor.cc
+++ b/src/algorithms/calorimetry/SimCalorimeterHitProcessor.cc
@@ -20,10 +20,9 @@
 #include <functional>
 #include <gsl/pointers>
 #include <limits>
+#include <map>
 #include <stdexcept>
 #include <tuple>
-#include <unordered_map>
-#include <map>
 #include <variant>
 #include <vector>