From bfd26e5302b4ba6fabcda07e74de76d0d565af24 Mon Sep 17 00:00:00 2001
From: Vakhtang Tsulaia <vakhtang.tsulaia@cern.ch>
Date: Thu, 16 Sep 2021 16:22:47 +0200
Subject: [PATCH] Merge branch 'race.GeneratorObjects-20210916' into 'master'
GeneratorObjects: Fix potential race.
See merge request atlas/athena!46528
(cherry picked from commit a5d2958c0edc0bcd99b3f35a78eff333156b319b)
a5176988 GeneratorObjects: Fix potential race.
---
.../src/HepMcParticleLink.cxx | 24 ++++++++++++-------
1 file changed, 15 insertions(+), 9 deletions(-)
diff --git a/Generators/GeneratorObjects/src/HepMcParticleLink.cxx b/Generators/GeneratorObjects/src/HepMcParticleLink.cxx
index d744c198a05a..0fbd7512e88a 100644
--- a/Generators/GeneratorObjects/src/HepMcParticleLink.cxx
+++ b/Generators/GeneratorObjects/src/HepMcParticleLink.cxx
@@ -1,5 +1,5 @@
/*
- Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+ Copyright (C) 2002-2021 CERN for the benefit of the ATLAS collaboration
*/
@@ -211,6 +211,11 @@ const HepMC::GenParticle* HepMcParticleLink::cptr() const
if (0 != pEvt) {
auto pp = HepMC::barcode_to_particle(pEvt,barcode());
+ // Be sure to update m_extBarcode before m_ptrs;
+ // otherwise, the logic in eventIndex() won't work correctly.
+ if (position != ExtendedBarCode::UNDEFINED) {
+ m_extBarcode.makeIndex (pEvt->event_number(), position);
+ }
if (pp) {
#ifdef HEPMC3
m_ptrs.set (sg, pp.get());
@@ -220,9 +225,6 @@ const HepMC::GenParticle* HepMcParticleLink::cptr() const
p=pp;
#endif
}
- if (position != ExtendedBarCode::UNDEFINED) {
- m_extBarcode.makeIndex (pEvt->event_number(), position);
- }
} else {
MsgStream log (Athena::getMessageSvc(), "HepMcParticleLink");
if (position != ExtendedBarCode::UNDEFINED) {
@@ -343,6 +345,15 @@ HepMcParticleLink::index_type HepMcParticleLink::eventIndex() const
if (pEvt) {
const int event_number = pEvt->event_number();
auto pp = HepMC::barcode_to_particle(pEvt,barcode());
+ // Be sure to update m_extBarcode before m_ptrs.
+ // Otherwise, if two threads run this method simultaneously,
+ // one thread could see index == UNDEFINED, but where m_ptr
+ // is already updated so we get nullptr back for sg.
+ if(event_number>-1) {
+ index = static_cast<index_type>(event_number);
+ m_extBarcode.makeIndex (index, position);
+ return index;
+ }
if (pp) {
#ifdef HEPMC3
m_ptrs.set (sg, pp.get());
@@ -350,11 +361,6 @@ HepMcParticleLink::index_type HepMcParticleLink::eventIndex() const
m_ptrs.set (sg, pp);
#endif
}
- if(event_number>-1) {
- index = static_cast<index_type>(event_number);
- m_extBarcode.makeIndex (index, position);
- return index;
- }
}
}
}
--
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