undefined pthread_join

[prachijpp]

Here is my code:

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<time.h>
#include<pthread.h>

pthread_t hour_thread , min_thread , sec_thread;
time_t rawtime;
struct tm *mytime;

void set_time() {
system("clear");
rawtime = time(&rawtime);
mytime = localtime(&rawtime);
printf("Current time : %s" , asctime(mytime));
}

void * update_hour(void *arg) {
while(1) {
sleep(1);
rawtime = time(&rawtime);
mytime = localtime(&rawtime);
set_time();
}
}

void * update_min(void *arg) {
while(1) {
sleep(1);
rawtime = time(&rawtime);
mytime = localtime(&rawtime);
set_time();
}
}

void * update_sec(void *arg) {
while(1) {
sleep(1);
rawtime = time(&rawtime);
mytime = localtime(&rawtime);
set_time();
}
}

int main() {
int err1 , err2 , err3;
void *value_ptr;

set_time();

if((err1 = pthread_create(&hour_thread , NULL , update_hour , NULL)) != 0)
printf("\n\tError in creating hour thread : %s" , strerror(err1));

if((err2 = pthread_create(&min_thread , NULL , update_min , NULL)) != 0)
printf("\n\tError in creating minute thread : %s" , strerror(err2));

if((err3 = pthread_create(&sec_thread , NULL , update_sec , NULL)) != 0)
printf("\n\tError in creating second thread : %s" , strerror(err3));

pthread_join(hour_thread , &value_ptr);
pthread_join(min_thread , &value_ptr);
pthread_join(sec_thread , &value_ptr);

return(0);
}


When I run it I get following error:

/tmp/ccsOiUW1.o: In function `main':
clock.c:(.text+0x13a): undefined reference to `pthread_create'
clock.c:(.text+0x182): undefined reference to `pthread_create'
clock.c:(.text+0x1ca): undefined reference to `pthread_create'
clock.c:(.text+0x203): undefined reference to `pthread_join'
clock.c:(.text+0x218): undefined reference to `pthread_join'
clock.c:(.text+0x22d): undefined reference to `pthread_join'
collect2: ld returned 1 exit status


Header file pthread.h gets included successfully,
so why it is not detecting function pthread_join, pthread_create

[slavik]

did you use option -lpthread ?

[dwhitney67]

It sure would be nice if you learned how to indent your code. Also, I hope this code will not be used for anything serious. With multiple threads running, and all using the same variables to stuff data into them, it's a wonder that your program works.

Btw, each thread is calling time(), localtime(), and then set_time(). The function set_time() is then calling time() and localtime(). Isn't this a little redundant?

If you agree, then remove the redundant calls from your threads. Then move the declarations for rawtime and mytime inside of set_time(). Then look into protecting the code within set_time() with a pthread_mutex.

I should also add that having the hours, minutes, and seconds threads are also redundant in themselves... unless you plan to do something special within each one at a later time.

[bunker]

Also localtime() is not thread-safe. You're better off using boost's replacement. Could save you some head-scratching in the future :).

[prachijpp]

Thanks a lot everyone!
I solved the problem. :)