A multithreading app compiled with MSVC fails at runtime

Question

I've implemented a class that cyclically runs a supplied function.

//Timer.h
#include <chrono>
#include <mutex>
#include <thread>

class Timer {
public:
    Timer(const std::chrono::milliseconds period, const std::function<void()>& handler);
    ~Timer();
    void Start();
    void Stop();
    bool IsRunning() const;

private:
    const std::function<void()>& handler;
    const std::chrono::milliseconds period;
    bool isRunning = false;
    mutable std::recursive_mutex lock;
    int counter = 0;

    void DoLoop(int id);
};

//Timer.cpp
#include "Timer.h"

Timer::Timer(const std::chrono::milliseconds period, const std::function<void()>& handler) :handler(handler), period(period), lock(){}

Timer::~Timer() {
    Stop();
}

void Timer::Stop() {
    lock.lock();
    isRunning = false;  
    lock.unlock();
}

void Timer::Start() {
    lock.lock();
    if (!isRunning) {
        isRunning = true;
        counter++;
        std::thread(&Timer::DoLoop, this, counter).detach();
    }
    lock.unlock();
}

void Timer::DoLoop(int id) {
    while (true){
        std::this_thread::sleep_for(period);
        lock.lock();
        bool goOn = isRunning && counter==id;
        if (goOn) std::thread(handler).detach();
        lock.unlock();

        if (!goOn)
            break;
    }
}

bool Timer::IsRunning() const {
    lock.lock();
    bool isRunning = this->isRunning;
    lock.unlock();
    return isRunning;
}

And here'a s simple program to see if it works:

void Tick(){ cout << "TICK" << endl; }

int main() {
    Timer timer(milliseconds(1000), Tick);
    timer.Start();
    cin.get();
}

When I build the app with g++, the program builds and runs without any problems. However, when I use the Microsoft's compiler (v18) the program compiles as well, but it fails at runtime.

When I use the release configuration I get the following exception from one of the threads:

Unhandled exception at 0x000007F8D8E14A30 (msvcr120.dll) in Program.exe: Fatal program exit requested.

When I use the debug configuration, a Microsoft Visual C++ Runtime Library error pops up every second:

Debug Error!

Program: ...\path\Program.exe

R6010 - abort() has been called

In both configurations:

• The exception is thrown/the errors start popping up in the second iteration of the timer's loop.

• The program does not enter the Tick function even once, even though thread(handler) gets invoked.

• Although the stack traces at the moment of error differ in those two configurations, neither of them contains anything from my code. Both start with ntdll.dll!UserThreadStart(); the debug one ends with msvcr123d.dll!_NMSG_WRITE() and the release one ends with msvcr120.dll!abort().

Why do the problems appear and why only when the app is compiled with MSVC? Is it some kind of MSVC's bug? Or maybe should I change something in the compiler's configuration?

Answer 1

Your thread is throwing std::bad_function_call, the exception is not handled so the run time is calling abort().

Changing:

const std::function<void()>& handler;

To

const std::function<void()> handler;

Fixes the problem. I guess this is because you are sharing it between threads?

Also works if you create a local and pass a reference to that:

  const std::function<void()> f = Tick;
  Timer timer(std::chrono::milliseconds(1000), f);

So it must have somehow gone out of scope.

Edit: Indeed the function object is destructed at after the ctor call. Not sure why this is.