assert_only_one_thread_test.cc

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#include "cetlib/SimultaneousFunctionSpawner.h"
#include "cetlib/assert_only_one_thread.h"

#include <chrono>
#include <thread>

using namespace cet;
using namespace std::chrono_literals;

// This test is 'fragile' in that, on a heavily loaded system, we
// might see:
//    1. all threads hit the "barrier" in SimultaneousFunctionSpawner
//    2. all threads start executing
//    3. one thread swaps out before getting to increment the counter
//        in the ThreadCounter.
//    4. the other thread completes (increments and then decrements
//        the counter)
//    5. the sappwed thread comes back, and is not running at the
//        same time as the other thread, so the expected violation
//        is not seen.

// We attempt to make this very rare by:
//    running a function that takes a long time, and
//    running many threads, hoping not all will swap out in
//    the right order so that we see NO overlaps.
int
main()
{
  CET_ASSERT_ONLY_ONE_THREAD();
  auto will_fail = [] {
    // Insert "by-hand" what the CET_ASSERT_ONLY_ONE_THREAD would
    // expand to so that we can avoid an std::abort() for testing.
    static cet::detail::ThreadCounter s{__FILE__, __LINE__, __func__};
    cet::detail::ThreadCounter::Sentry hold{s, false};
    std::this_thread::sleep_for(100ms);
  };
  SimultaneousFunctionSpawner launch{repeated_task(10u, will_fail)};
}