possible_dr.cpp

#include <array>
#include <atomic>
#include "./blockingconcurrentqueue.h"

using namespace std::chrono_literals;

// global counter
// * the program can exit when it reaches 1000
// * incremented by tasks
std::atomic<int> ctr{0};

// task 
// * non-copyable
// * increments `ctr` on construction
// * transfers some mock state `x` on moves
struct task
{
    int x = 0;

    task()
    {
        ++ctr;
    }

    task(const task&) = delete;
    task& operator=(const task&) = delete;

    task(task&& rhs) : x{rhs.x}
    {
    }

    task& operator=(task&& rhs)
    {
        x = rhs.x;
        return *this;
    }
};

// task queue
moodycamel::BlockingConcurrentQueue<task> q;

// worker
// * contains thread that constantly calls `wait_dequeue`
// * on dtor, spawns tasks until thread is joined
struct worker
{
    std::thread th;
    std::atomic<bool> running{true};
    std::atomic<bool> exited{false};

    worker()
    {
        th = std::thread([this]
            {
                task t;
                while(running)
                {
                    q.wait_dequeue(t);
                }
                exited = true;
            });
    }

    ~worker()
    {
        running = false;

        while(!exited)
        {
            q.enqueue(task{});
            std::this_thread::sleep_for(1ms);
        }

        th.join();
    }
};

int main()
{
    // create 8 workers
    std::array<worker, 8> ws;

    // enqueue 1000 tasks
    for(int i = 0; i < 1000; ++i)
    {
        q.enqueue(task{});
    }

    // wait for `ctr` to be `>= 1000`
    while(ctr < 1000)
    {
        std::this_thread::sleep_for(1ms);
    }
}

threadsan_output.txt

WARNING: ThreadSanitizer: data race (pid=15381)
  Read of size 4 at 0x7d340000cf48 by thread T7:
    #0 task::operator=(task&&) <null> (a.out+0x000000402c36)
    #1 bool moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::ImplicitProducer::dequeue<task>(task&) <null> (a.out+0x000000406279)
    #2 bool moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::ProducerBase::dequeue<task>(task&) <null> (a.out+0x000000405340)
    #3 bool moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::try_dequeue<task>(task&) <null> (a.out+0x0000004044e9)
    #4 void moodycamel::BlockingConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::wait_dequeue<task>(task&) <null> (a.out+0x000000403303)
    #5 worker::worker()::{lambda()#1}::operator()() const <null> (a.out+0x000000402ce6)
    #6 void std::_Bind_simple<worker::worker()::{lambda()#1} ()>::_M_invoke<>(std::_Index_tuple<>) <null> (a.out+0x00000040a1a4)
    #7 std::_Bind_simple<worker::worker()::{lambda()#1} ()>::operator()() <null> (a.out+0x00000040a0dd)
    #8 std::thread::_State_impl<std::_Bind_simple<worker::worker()::{lambda()#1} ()> >::_M_run() <null> (a.out+0x00000040a018)
    #9 execute_native_thread_routine /build/gcc-multilib/src/gcc/libstdc++-v3/src/c++11/thread.cc:83 (libstdc++.so.6+0x0000000baaae)

  Previous write of size 8 at 0x7d340000cf48 by main thread:
    #0 malloc /build/gcc-multilib/src/gcc/libsanitizer/tsan/tsan_interceptors.cc:538 (libtsan.so.0+0x000000026aac)
    #1 moodycamel::ConcurrentQueueDefaultTraits::malloc(unsigned long) <null> (a.out+0x000000402102)
    #2 moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::Block* moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::create<moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::Block>() <null> (a.out+0x00000040880b)
    #3 moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::Block* moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::requisition_block<(moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::AllocationMode)0>() <null> (a.out+0x000000407add)
    #4 bool moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::ImplicitProducer::enqueue<(moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::AllocationMode)0, task>(task&&) <null> (a.out+0x000000406ed4)
    #5 bool moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::inner_enqueue<(moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::AllocationMode)0, task>(task&&) <null> (a.out+0x0000004057eb)
    #6 moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::enqueue(task&&) <null> (a.out+0x0000004049c6)
    #7 moodycamel::BlockingConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::enqueue(task&&) <null> (a.out+0x00000040343e)
    #8 main <null> (a.out+0x0000004016dd)

  Location is heap block of size 208 at 0x7d340000cf30 allocated by main thread:
    #0 malloc /build/gcc-multilib/src/gcc/libsanitizer/tsan/tsan_interceptors.cc:538 (libtsan.so.0+0x000000026aac)
    #1 moodycamel::ConcurrentQueueDefaultTraits::malloc(unsigned long) <null> (a.out+0x000000402102)
    #2 moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::Block* moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::create<moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::Block>() <null> (a.out+0x00000040880b)
    #3 moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::Block* moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::requisition_block<(moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::AllocationMode)0>() <null> (a.out+0x000000407add)
    #4 bool moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::ImplicitProducer::enqueue<(moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::AllocationMode)0, task>(task&&) <null> (a.out+0x000000406ed4)
    #5 bool moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::inner_enqueue<(moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::AllocationMode)0, task>(task&&) <null> (a.out+0x0000004057eb)
    #6 moodycamel::ConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::enqueue(task&&) <null> (a.out+0x0000004049c6)
    #7 moodycamel::BlockingConcurrentQueue<task, moodycamel::ConcurrentQueueDefaultTraits>::enqueue(task&&) <null> (a.out+0x00000040343e)
    #8 main <null> (a.out+0x0000004016dd)

  Thread T7 (tid=15389, running) created by main thread at:
    #0 pthread_create /build/gcc-multilib/src/gcc/libsanitizer/tsan/tsan_interceptors.cc:876 (libtsan.so.0+0x000000028360)
    #1 __gthread_create /build/gcc-multilib/src/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/x86_64-pc-linux-gnu/bits/gthr-default.h:662 (libstdc++.so.6+0x0000000badc4)
    #2 std::thread::_M_start_thread(std::unique_ptr<std::thread::_State, std::default_delete<std::thread::_State> >, void (*)()) /build/gcc-multilib/src/gcc/libstdc++-v3/src/c++11/thread.cc:163 (libstdc++.so.6+0x0000000badc4)
    #3 worker::worker() <null> (a.out+0x000000402da3)
    #4 std::array<worker, 8ul>::array() <null> (a.out+0x000000402f80)
    #5 main <null> (a.out+0x0000004016b0)

SUMMARY: ThreadSanitizer: data race (a.out+0x402c36) in task::operator=(task&&)
==================