[boost] [thread] Does this condition wrapper perform better than the wrapped condition?

From: vicente.botet (vicente.botet_at_[hidden])
Date: 2008-05-19 16:11:12

Hello,

In the Join library I have see the following idiom

    mutex mtx;
    condition_variable cond;
    unsigned num_blocked;

    void foo() {
        unique_lock l(mtx);
        ++num_blocked;
        cond.wait(lock);
        --num_blocked;
    
        // ...
    }

    void foo() {
        unique_lock l(mtx);
        // ...
        if (num_blocked > 0) cond.notify_one();
        // ...
    }

Does this perform better in some contexts? if yes in which ones?

If yes, does this justify a condition wrapper like:

template <
    class Condition
> 
class condition_booster{
public:
    typedef Condition condition; 
    void notify_one() { if (num_blocked > 0) cond.notify_one(); }
    void notify_all() { if (num_blocked > 0) cond.notify_all(); }
    template <typename Locker, typename Predicate>
    template <typename Locker>
    void wait(Locker& lock) {
        ++num_blocked;
        cond.wait(lock);
        --num_blocked;
    }
    void wait(Locker& lock, Predicate& pred) {
        while(!pred()) wait(lock);
    }
    // ...
private:
    Condition cond;
    unsigned num_blocked;
};

Best
_____________________
Vicente Juan Botet Escriba