C++ segmentation fault when throwing in ordered OMP parallel for

Question

the code below crashes with

terminate called after throwing an instance of 'std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >'
Aborted                    (core dumped) ./a.out

when compiled with g++ -fopenmp

#include <string>
#include <vector>
#include <iostream>
void bla2(){
  try{
    throw std::string("bla2");
  }catch(std::string x){
    throw std::string("error ")+x;
  }
}
void bla1(){
  try{
    std::vector<std::string> y;
    y.resize(10);
#pragma omp parallel for ordered schedule(static) num_threads(10)
    for(int i=0;i<10;++i){
      try{
#pragma omp ordered
        {
          bla2();
        }
      }catch(std::string x){
        y[i]=x;
      }
    }
    for(auto &x:y) if(x.size()>0) throw x;
  }catch(std::string x){
    throw std::string("error ")+x;
  }
}

int main(){
  try{
    bla1();
  }catch(std::string x){
    std::cout<<x<<std::endl;
  }
}

Note that the segmentation fault can be avoid by omitting #pragma omp ordered

OS: Linux kernel 6.17.5

g++: 15.2.1

Any suggestions?

The standard spells it out: "A throw executed inside a ordered region must cause execution to resume within the same ordered region, and the same thread that threw the exception must catch it." — Homer512
– Homer512, Commented Oct 31 at 15:09
By the way, throwing a std::string is not a good idea. Moreover, you should catch object by reference so to avoid necessary copies in this case. Catching an exception from a parallel section seems a red flag to me (I highly doubt this is supported), independently of the ordered construct. Finally, a parallel for with only an ordered construct is useless performance wise (no actual parallelism). Please note that using num_threads(10) is also a bad idea in real-world application (OK for a prototype). — Jérôme Richard
– Jérôme Richard, Commented Oct 31 at 15:25
Side note: Exceptions should generally be caught by const & (const reference). — Jesper Juhl
– Jesper Juhl, Commented Oct 31 at 19:53
@JérômeRichard Catching exceptions from another thread can't be supported without code that's OMP almost certainly doesn't have. Exceptions merely unwind a thread's call stack in a way that's different from return. — Andrew Henle
– Andrew Henle, Commented Oct 31 at 20:19

user1407220 · Accepted Answer · 2025-11-01 00:45:54Z

1

This works:

#include <string>
#include <vector>
#include <iostream>
void bla2(){
  try{
    throw std::string("bla2");
  }catch(std::string x){
    throw std::string("error ")+x;
  }
}
void bla1(){
  try{
    std::vector<std::string> y;
    y.resize(10);
#pragma omp parallel for ordered schedule(static) num_threads(10)
    for(int i=0;i<10;++i){
      try{
         //do some heavy work here 
#pragma omp ordered
        {
          try{
            bla2();
          }catch(std::string x){
            y[i]=x;
          }
        }
      }catch(std::string x){
        y[i]=x;
      }
    }
    for(auto &x:y) if(x.size()>0) throw x;
  }catch(std::string x){
    throw std::string("error ")+x;
  }
}

int main(){
  try{
    bla1();
  }catch(std::string x){
    std::cout<<x<<std::endl;
  }
}

answered Nov 1 at 0:45

user1407220

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