Is this a reliable way to test for multiple threads entering the critical section?

[vapid cove]

void runSomething()
{
static std::atomic<size_t> threadCount(0);
threadCount += 1;
run_critical_section(args...);
if(threadCount.load() != 1)
{
std::cerr<<"race condition caught, terminating...\n";
exit(1);
}
threadCount -= 1;
}

[vapid quartz]

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void runSomething() {
  static std::atomic<size_t> threadCount(0);
  threadCount += 1;
  run_critical_section(args...);
  if (threadCount.load() != 1) {
    std::cerr << "race condition caught, terminating...\n";
    exit(1);
  }
  threadCount -= 1;
}

Kolio98

[near berry]

I don't see any issue with the approach

the problem is that the UB has already occured at the point where you're checking

but the detection is correct

it also gives false positives for when threadCount has been incremented, but the critical section hasn't been entered yet, but that's a really minor issue and doesn't look preventable

[grim smelt]

Arguably you don't even attempt to detect multiple threads entering the critical section. You should really check before entering, not (only) after.

[vapid cove]

a.k.a. the atomic counter should be placed at the first line in the actual critical section, right?

[near berry]

you could use an atomic fetch-add to check if you're entering the critical section at the same time as another thread

if (threadCount++ != 0) {
    // error because race condition
}
critical_section();
threadCount--;

[vapid cove]

!solved