std::future.get() sometimes stuck in os x - c++

Question

I have two threads, one thread should receive and process requests from another. The second is to transfer requests and receive a response synchronously. I tried the following scheme: queue of pair (value, promise). The first thread creates a promise and pushed it in synchronous queue and waiting for a return value by future.get()
The problem is that sometimes the thread stuck on future.get(), but when i pause program execution and continue it again works correctly. this stucks has random nature.
FutureQueue.h
#ifndef FutureQueue_h
#define FutureQueue_h
#include <queue>
#include <future>
#include <thread>
#include <mutex>
#include <condition_variable>
template <typename T, typename R>
class Work{
public:
Work(){
}
Work(T value, std::promise<R>* promise){
m_value = value;
m_p_promise = promise;
}
std::promise<R>* m_p_promise;
T m_value;
public:
T getValue(){
return m_value;
}
void setResult(R result){
m_p_promise->set_value(result);
}
};
template <typename T, typename R>
class FutureQueue
{
public:
Work<T,R> getWork(){
auto p = pop();
return Work<T,R>(p.first,p.second);
}
R execute(T value)
{
std::promise<R> promise = std::promise<R>();
std::future<R> f = promise.get_future();
auto p = std::pair<T, std::promise<R>*>(value, &promise);
push(p);
return f.get();
}
private:
std::pair<T,std::promise<R>*> pop(){
std::unique_lock<std::mutex> mlock(mutex_);
while (queue_.empty())
{
cond_.wait(mlock);
}
auto item = queue_.front();
queue_.pop();
return item;
}
void push(const std::pair<T,std::promise<R>*>& item){
std::unique_lock<std::mutex> mlock(mutex_);
queue_.push(item);
mlock.unlock();
cond_.notify_one();
}
std::queue<std::pair<T,std::promise<R>*>> queue_;
std::mutex mutex_;
std::condition_variable cond_;
};
#endif
main.cpp
#include <iostream>
#include <thread>
#include "FutureQueue.h"
using namespace std;
atomic<bool> quit;
FutureQueue<int, int> mQueue;
void consumer(){
Work<int,int> work;
while(true){
work = mQueue.getWork();
if (quit){
break;
}
int value = work.getValue()+100;
work.setResult(value);
}
work.setResult(0);
}
int main(int argc, const char * argv[]) {
quit = false;
thread thread(consumer);
// test 2
for (int i=0;i<100000;i++){
int value = mQueue.execute(i);
cout << "input " << i <<" execute result " << value << endl;
}
quit = true;
mQueue.execute(-1);
thread.join();
return 0;
}
I don't know whats wrong with this code, maybe you can suggest better solution. Thank you
UPDATE
Stucks occurs only in os x with Apple LLVM version 6.0
There is no problem under gcc on OS X and Linux and Visual studio on Windows

Answer 1

There are two threads, A with
for (int i=0;i<100000;i++){
int value = mQueue.execute(i);
cout << "input " << i <<" execute result " << value << endl;
}
quit = true;
mQueue.execute(-1);
B with
thread thread(consumer);
You expect B first Run, then stuck because
while (queue_.empty())
{
cond_.wait(mlock);
}
B will continue run until A run the following code
cond_.notify_one();
Usually it will be ok. But if A first fun "cond.notify_one()", the B call "con_.wait(mlock)", the B will be stuck forever.