I try to wait the main function, till the threads finish their work. But the main function finish its work and exit. I think because of that the threads has not the correct pointers/values in the variables.(tally and steps)
Does someone know how to use waitpid/wait properly in this case?
my Code:
#define _GNU_SOURCE
#include <stdio.h>
#include <inttypes.h> /* for PRIu64 and uint64_t */
/* you'll need further includes */
#include <sched.h>
#include <stdlib.h>
#include "tally.h"
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#define STACK_SIZE 32768
#define THREADS 2
struct clone_args{
uint64_t steps;
uint64_t* tally;
};
int incHelper(void* arg){
struct clone_args *args = (struct clone_args*)arg;
uint64_t steps= args->steps;
uint64_t* tally = args->tally;
increment(tally,steps);
(void) arg;
(void) tally;
(void) steps;
exit(2);
return 0;
}
int main ()
{
uint64_t N = 10000000;
uint64_t tally = 1;
tally_init();
int thread_pid[THREADS];
int status;
for(int i= 0; i<THREADS;i++){
void *child_stack = malloc(STACK_SIZE);
struct clone_args *arguments = malloc(sizeof(struct clone_args));
arguments->steps = N;
arguments->tally = &tally;
void* arg = (void*) &arguments;
thread_pid[i] = clone(incHelper, child_stack+STACK_SIZE,CLONE_VM, arg);
pid_t pid = waitpid(thread_pid[i],&status,SIGCHLD);
printf("C-PID [%d]\n", thread_pid[i]);
(void) pid;
}
tally_clean();
printf( "\nTally is %" PRIu64 "\n", tally );
(void) N;
(void) thread_pid;
(void) tally;
(void) status;
printf("\n MAIN PROGRAMM END\n");
return 0;
}
The increment function:
/* modify this function to achieve correct parallel incrementation */
void increment ( uint64_t *tally, uint64_t steps )
{
printf("\nTALLY: %"PRIu64"\n",*tally);
printf("STEPS: %"PRIu64"\n",steps);
for( uint64_t i = 0; i < steps; i++ )
{
*tally += 1;
}
return;
}
The Result i got after running the code:
C-PID [29819]
C-PID [29820]
Tally is 1
MAIN PROGRAMM END
root@...(~/Downloads/asst3/asst3-clone)$
TALLY: 0
STEPS: 140714329004032
TALLY: 888309
STEPS: 140714329004032
The code should increment a variable with two threads. To avoid criticalsection Problem i should use semaphores. But thats an other exercise. First exercise it to use clone() function to create two threads. I dont understand, if the flags of clone() are wrong or my code is completely wrong. I am new at programming language C.
I spent last 12 hours of searching with google.
I thank for every answer :).
Sorry for bad english.
Regards
