Question

I have created two threads and i want to see their priority after they are created :-
for this I have written the following code :-

   #include <iostream>
   #include <unistd.h>
   #include <pthread.h>
   #include <sched.h>
   #include <string.h>
   #include <errno.h>
   int main()
   { //something
     struct sched_param main_param, t1_param, t2_param;
     pthread_t t1, t2;
      int *sched1, *sched2;
     if (pthread_create(&t1, NULL, fn1, NULL) != 0) // inside fn1 thread sleeps in loop
      {
        std::cout << "couldn't create t1" << std::endl;
        return -1;
       }
     if (pthread_create(&t2, NULL, fn2, NULL) != 0)  //inside fn2 thread sleeps in loop
      {
        std::cout << "couldn't create t2" << std::endl;
        return -1;
      }

   if (pthread_getschedparam(t1, sched1, &t1_param) != 0) 
     {
       std::cout << "error setting priority for T1: (" << errno << "), " << 
        strerror(errno) << std::endl;
     }
  std::cout << "t1 thread will have a prio of " << t1_param.sched_priority << std::endl;
   if (pthread_getschedparam(t1, sched2, &t1_param) != 0) 
     {
       std::cout << "error setting priority for T1: (" << errno << "), " << 
       strerror(errno) << std::endl;
     }
   std::cout << "t2 thread will have a prio of " << t2_param.sched_priority <<std::endl;

 // something 
 } 

only when i add code related to pthread_getschedparam i am getting the segmentation fault else the code works fine . Am i doing something wrong here ? I even tried replacing arhument sched1 and sched2 by NULL

Answer 1

You declared pointers sched1 and sched2 of type int* but never initialised those pointers. You need to allocate int variables and then pass pointers to those variables.

Like this:

int sched1, sched2;
.....
if (pthread_getschedparam(t1, &sched1, ....