C++ lock_guard

Table of contents

std::mutex mtx;

void print_even_or_throw( int x )
{
  if( x % 2 == 0 ) {
    fmt::print( "{} is even\n", x );
  }
  else {
    throw( std::logic_error( fmt::format( "💥 {} is not even", x ) ) );
  }
}

void print_thread_id( int id )
{
  try {
    // using a local lock_guard to lock mtx guarantees unlocking on destruction
    std::lock_guard<std::mutex> lck( mtx );
    print_even_or_throw( id );
  }
  catch( std::logic_error &e ) {
    fmt::print( "[exception caught] {} -> {}\n", id, e.what() );
  }
}

int main()
{
  std::thread threads[10];
  // spawn 10 threads:
  for( int i = 0; i < 10; ++i ) {
    threads[i] = std::thread( print_thread_id, i + 1 );
  }

  for( auto &th : threads ) {
    th.join();
  }

  return 0;
}

Possible output

[exception caught] 9 -> 💥 9 is not even
8 is even
6 is even
[exception caught] 7 -> 💥 7 is not even
[exception caught] 3 -> 💥 3 is not even
2 is even
[exception caught] 1 -> 💥 1 is not even
4 is even
[exception caught] 5 -> 💥 5 is not even
10 is even

References

• cplusplus.com - lock_guard