create thread - passing arguments - c

Question

I am attempting on creating multiple threads that each thread calculates a prime. I am trying to pass a second argument to a function using thread create. It keeps throwing up errors.
void* compute_prime (void* arg, void* arg2)
{
here is my main() with the create thread. &primeArray[i] after &max_prime is giving me the errors.
for(i=0; i< num_threads; i++)
{
primeArray[i]=0;
printf("creating threads: \n");
pthread_create(&primes[i],NULL, compute_prime, &max_prime, &primeArray[i]);
thread_number = i;
//pthread_create(&primes[i],NULL, compPrime, &max_prime);
}
/* join threads */
for(i=0; i< num_threads; i++)
{
pthread_join(primes[i], NULL);
//pthread_join(primes[i], (void*) &prime);
//pthread_join(primes[i],NULL);
//printf("\nThread %d produced: %d primes\n",i, prime);
printf("\nThread %d produced: %d primes\n",i, primeArray[i]);
sleep(1);
}
the error i get is:
myprime.c: In function âmainâ:
myprime.c:123: warning: passing argument 3 of âpthread_createâ from incompatible pointer type
/usr/include/pthread.h:227: note: expected âvoid * (*)(void *)â but argument is of type âvoid * (*)(void *, void *)â
myprime.c:123: error: too many arguments to function âpthread_createâ
It works fine if i take out the second argument.

Answer 1

You can only pass a single argument to the function that you are calling in the new thread. Create a struct to hold both of the values and send the address of the struct.
#include <pthread.h>
#include <stdlib.h>
typedef struct {
//Or whatever information that you need
int *max_prime;
int *ith_prime;
} compute_prime_struct;
void *compute_prime (void *args) {
compute_prime_struct *actual_args = args;
//...
free(actual_args);
return 0;
}
#define num_threads 10
int main() {
int max_prime = 0;
int primeArray[num_threads];
pthread_t primes[num_threads];
for (int i = 0; i < num_threads; ++i) {
compute_prime_struct *args = malloc(sizeof *args);
args->max_prime = &max_prime;
args->ith_prime = &primeArray[i];
if(pthread_create(&primes[i], NULL, compute_prime, args)) {
free(args);
//goto error_handler;
}
}
return 0;
}

Answer 2

In case of std::thread, the user can pass arguments to the thread function in the following method
std::thread(funcName,arg1,arg2);
for instance,
//for a thread function,
void threadFunction(int x,int y){
std::cout << x << y << std::endl;
}
// u can pass x and y values as below
std::thread mTimerThread;
mTimerThread = std::thread(threadFunction,1,12);

Answer 3

This is the code of Manakarse , everything is really good but you need a
pthread_join(thread[i],NULL)
just to be sure all of threads will successfully execute before end of main thread("main will "waiting" while all of threads aren't finished yet)
;

Answer 4

#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
typedef struct
{
int stop_flag;
char name[30];
} _process_data;
typedef struct
{
int meter_no;
int port_no;
} _process_control;
typedef struct
{
_process_data *process_data;
_process_control *process_control;
} compute_prime_struct;
void *compute_prime (void *args)
{
compute_prime_struct *actual_args = args;
printf("actual_args->process_data->stop_flag [%d]\n",actual_args->process_data->stop_flag);
printf("actual_args->process_data->name [%s]\n",actual_args->process_data->name);
printf("actual_args->process_control->meter_no [%d]\n",actual_args->process_control->meter_no);
printf("actual_args->process_control->port_no [%d]\n",actual_args->process_control->port_no);
free(actual_args);
return 0;
}
void fill_data(_process_data *process_data,_process_control *process_control)
{
process_data->stop_flag=1;
process_data->name[0]='P';
process_control->meter_no=6;
process_control->port_no=22;
pthread_t tid;
compute_prime_struct *args = malloc(sizeof (*args));
args->process_data = malloc(sizeof (*args->process_data));
args->process_control = malloc(sizeof (*args->process_control));
memcpy (args->process_data, process_data, sizeof (args->process_data));
memcpy (args->process_control, process_control, sizeof (*args->process_control));
if(pthread_create(&tid, NULL, compute_prime, args))
{
free(args);
printf("Error here");
}
sleep(1);
}
int main()
{
_process_data process_data;
_process_control process_control;
fill_data(&process_data,&process_control);
return 0;
}