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c++multithreadingpthreads
Haohao Chang
Haohao Chang

Reputation: 57

C++ will thread created in class share the same class variable?

I have a class like this

class ThreadPool
{
public:
    ThreadPool();
    ThreadPool(int total_thread);
    ~ThreadPool();
    void active_pool(void);
    void* thread_start_routine(void* run_data);

private:
    int total_thread_;
    queue<TASK*> task_queue;
    sem_t* task_queue_mutex_;//Same function as mutex semaphore in P-C problem.
    sem_t* task_queue_full_;//Same function as full semaphore in P-C problem.
};

And I will create multiple thread within the active_pool function and each thread entry-function is thread_start_routine.

My question is that if each have to push/pop with queue task_queue, will all threads see the same queue or each queue they see is just a local copy through thread creation

Thank you~

Upvotes: 1

Views: 961

Answers (1)

Bathsheba
Bathsheba

Reputation: 234785

All threads will see the same queue. That's the beauty of concurrent programming. (You can use thread_local storage duration if you want a different instance per thread - this is a new addition to C++ since C++11.)

Normally, you need to make sure the relevant members are used in a thread-safe manner. Atomic types (std::atomic from C++11) and mutual exclusion units (std::mutex from C++11) are used for that.

References:

http://en.cppreference.com/w/cpp/keyword/thread_local

http://en.cppreference.com/w/cpp/atomic/atomic

http://en.cppreference.com/w/cpp/thread/mutex

Upvotes: 2

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