From e3a98af4ffbd93cf9edfd84c0bb862918aece1c2 Mon Sep 17 00:00:00 2001
From: Chris Jones <chrisdjones15@gmail.com>
Date: Tue, 19 May 2015 10:11:03 -0500
Subject: [PATCH] Make 10MB the default stack size for additional threads

Many of our ROOT files require very deep stacks in order to be able to read back certain branches. When read on a non-main thread the default stack size used by TBB is often too small. 10MB appears to be sufficiently large.
---
 FWCore/Framework/bin/cmsRun.cpp | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/FWCore/Framework/bin/cmsRun.cpp b/FWCore/Framework/bin/cmsRun.cpp
index 90537eba2b8a5..dc7c1da942fa5 100644
--- a/FWCore/Framework/bin/cmsRun.cpp
+++ b/FWCore/Framework/bin/cmsRun.cpp
@@ -54,6 +54,7 @@ static char const* const kHelpOpt = "help";
 static char const* const kHelpCommandOpt = "help,h";
 static char const* const kStrictOpt = "strict";
 
+constexpr unsigned int kDefaultSizeOfStackForThreadsInKB = 10*1024; //10MB
 // -----------------------------------------------
 namespace {
   class EventProcessorWithSentry {
@@ -235,7 +236,7 @@ int main(int argc, char* argv[]) {
       if(vm.count(kNumberOfThreadsOpt)) {
         setNThreadsOnCommandLine=true;
         unsigned int nThreads = vm[kNumberOfThreadsOpt].as<unsigned int>();
-        unsigned int stackSize=0;
+        unsigned int stackSize=kDefaultSizeOfStackForThreadsInKB;
         if(vm.count(kSizeOfStackForThreadOpt)) {
           stackSize=vm[kSizeOfStackForThreadOpt].as<unsigned int>();
         }
@@ -295,8 +296,8 @@ int main(int argc, char* argv[]) {
             auto const& ops = pset->getUntrackedParameterSet("options");
             if(ops.existsAs<unsigned int>("numberOfThreads",false)) {
               unsigned int nThreads = ops.getUntrackedParameter<unsigned int>("numberOfThreads");
-              unsigned int stackSize=0;
-              if(ops.existsAs<unsigned int>("sizeOfStackForThreadsInKB",0)) {
+              unsigned int stackSize=kDefaultSizeOfStackForThreadsInKB;
+              if(ops.existsAs<unsigned int>("sizeOfStackForThreadsInKB",false)) {
                 stackSize = ops.getUntrackedParameter<unsigned int>("sizeOfStackForThreadsInKB");
               }
               const auto nThreadsUsed = setNThreads(nThreads,stackSize,tsiPtr);