Creating a thread and passing input through the parent - c

Question

I'm trying to use a mutex to make a thread wait for user input from the parent thread. The current problem I'm facing is that the child doesn't wait, even though I have a mutex to lock and unlock, then I also join it in the parent thread. Also, I am currently unsure if my struct is being used correctly? Is the main() and *chthread() using the same instance of "lock"? I understand that when I get the user input BEFORE the thread creation that it works, however requirements of this exercise states it is meant to pass information after the thread is created.
#define _GNU_SOURCE
#include <stdio.h>
#include <pthread.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <readline/readline.h>
#include <readline/history.h>
# define BUFFER_SIZE 256
void *chthread(void *arg);
struct {
pthread_t pth;
pthread_mutex_t lock;
int ret;
void* ex;
} muinfo;
int main(int argc, char *argv[])
{
//struct mutex args;
char line[BUFFER_SIZE];
char *temp = NULL;
pthread_mutex_init(&muinfo.lock, NULL);
if((pthread_create(&muinfo.pth, NULL, chthread, line)) != 0) {
perror("Problem creating thread");
}
using_history();
temp = readline("enter a string: ");
strcpy(line, temp);
if((pthread_join(muinfo.pth, &muinfo.ex)) !=0) {
perror("Thread join error");
}
free(temp);
pthread_mutex_destroy(&muinfo.lock);
pthread_exit(NULL);
}
void *chthread(void *arg)
{
//struct mutex args;
pthread_mutex_lock(&muinfo.lock);
char *line = (char*)arg;
printf("testing %s\n", line);
pthread_mutex_unlock(&muinfo.lock);
pthread_exit(&muinfo.ret);
//return NULL;
}

Answer 1

As for your main problem, you need to lock mutex at main first(likely after init it),
and unlock it after getting input from user,
so the child thread will wait until main unlock.
pthread_mutex_init(&muinfo.lock, NULL);
pthread_mutex_lock(&muinfo.lock);
if((pthread_create(&muinfo.pth, NULL, chthread, line)) != 0) {
perror("Problem creating thread");
}
using_history();
temp = readline("enter a string: ");
strcpy(line, temp);
pthread_mutex_unlock(&muinfo.lock);
I remove using_history() and use delayed strcpy fixed string instead readline as test,
and it work fine for me.