How to give priority to privileged thread in mutex locking?

Question

First of all: I am completely a newbie in mutex/multithread programming, so sorry for any error in advance...

I have a program that runs multiple threads. The threads

Answer 1

On linux you can check this man: pthread_setschedparam and also man sched_setscheduler

pthread_setschedparam(pthread_t thread, int policy, const struct sched_param *param);

Check this also for c++2011: http://msdn.microsoft.com/en-us/library/system.threading.thread.priority.aspx#Y78

Answer 2

Try something like the following. You could make the class a thread-safe singleton and you could even make it a functor.

#include <pthread.h>
#include <semaphore.h>
#include <map>

class ThreadPrioFun
{
    typedef std::multimap<int, sem_t*> priomap_t;
public:
    ThreadPrioFun()
    {
        pthread_mutex_init(&mtx, NULL);
    }
    ~ThreadPrioFun()
    {
        pthread_mutex_destroy(&mtx);
    }
    void fun(int prio, sem_t* pSem)
    {
        pthread_mutex_lock(&mtx);
        bool bWait = !(pm.empty());
        priomap_t::iterator it = pm.insert(std::pair<int, sem_t*>(prio, pSem) );
        pthread_mutex_unlock(&mtx);

        if( bWait ) sem_wait(pSem);

        // do the actual job
        // ....
        //

        pthread_mutex_lock(&mtx);
        // done, remove yourself
        pm.erase(it);
        if( ! pm.empty() )
        {
             // let next guy run:
            sem_post((pm.begin()->second));
        }
        pthread_mutex_unlock(&mtx);
    }
private:
    pthread_mutex_t mtx;
    priomap_t pm;
};