Unlocks all pthread mutexes in mutex array - c

Question

Im trying to write a function that unlocks all pthread mutexes provided in an array of mutexes.
The array is mutexv and the number of mutexes in given by mutexc.
The function should return 0 on success,
-1 otherwise.
my function so far:
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <alloca.h>
#include "pthread.h"
#include "multi_mutex.h"
int multi_mutex_unlock(pthread_mutex_t **mutexv, int mutexc)
{
(void) mutexv;
(void) mutexc;
pthread_mutex_init(*mutexv, NULL);
for (int i=0; i<mutexc; i++){
if (pthread_mutex_unlock(*mutexv) !=0){
return -1;
}
}
return 0;
}
having a hard time figuring out what im doing wrong.

Answer 1

// correct type for specifying array sizes is size_t, not int:
int multi_mutex_unlock(pthread_mutex_t **mutexv, size_t mutexc)
{
// you wouldn't initialize here, that needs to occur much earlier
//pthread_mutex_init(*mutexv, NULL);
for (size_t i = 0; i < mutexc; i++)
{
if (pthread_mutex_unlock(mutexv[i]) != 0)
// you need to index properly ^^^
{
return -1;
}
}
return 0;
}
Actually a while loop can be more elegant:
int multi_mutex_unlock(pthread_mutex_t **mutexv, size_t mutexc)
{
while(mutexc)
{
if (pthread_mutex_unlock(*mutexv) != 0)
{
return -1;
}
mutexc--; // decrement the remaining number
mutexv++; // increment the pointer to point to next mutex
}
return 0;
// or totally compact as:
for(; mutexc; --mutexc, ++mutexv)
{
if (pthread_mutex_unlock(*mutexv) != 0)
{
return -1;
}
}
}
Finally: You don't give any information on how many mutexes actually could be unlocked (or alternatively, how many have not) – you might return that number instead of -1, then any value different from originally passed mutexc would mean an error occurred.