c - Not able to find the bug in my multithreading program? -

i have implemented simple multithreading program, producer access global variable , fills it, after consumner prints it.

i have written main

#include<stdio.h> #include<stdlib.h> #include<pthread.h>  void *prod(void); void *cons(void);  unsigned int my_var = 0;  pthread_mutex_t mut = pthread_mutex_initializer;  int main() {     pthread_t th1, th2;     int status;      status = pthread_create(&th1, null, (void*)prod, null);     if(status)     {         printf("error creating thread 1 : %d\n", status);         exit(-1);     }     status = pthread_create(&th2, null, (void*)cons, null);     if(status)     {          printf("error creating thread 2 : %d\n", status);          exit(-1);     }      pthread_join(th1, null);     pthread_join(th2, null);      return 0; } 

my producer function goes :

void *prod(void) {     while(1)     {         pthread_mutex_unlock(&mut);         printf("enter value : ");         scanf("%d", &my_var);     } } 

consumer function :

void *cons(void) {     while(1)     {         printf("the value entered %d\n", my_var);         pthread_mutex_lock(&mut);     } } 

this program runs exact output pattern different, :

enter value : value entered 0 value entered 0 45 enter value : value entered 45 85 enter value : value entered 85 12 enter value : value entered 12 67 enter value : value entered 67 49 enter value : value entered 49 

i finding difficult rectify logic new threading concept. please me out in resolving issue.

my expected output :

enter value : 45 value entered 45 ......................................... 

after answer's , guidelines use mutex_cond_var. used them in function :

void *prod(void) {     while(1)     {         printf("enter value : ");         scanf("%d", &my_var);         pthread_cond_signal(&condition_var1);         pthread_mutex_unlock(&mut);     }   }  void *cons(void) {     while(1)     {         pthread_mutex_lock(&mut);         pthread_cond_wait( &condition_var1, &mut );         printf("the value entered %d\n", my_var);     } } 

resulted output :

enter value : 78 enter value : value entered 78 86 enter value : 15 enter value : value entered 15 35 enter value : 86 enter value : value entered 86 12 enter value : 65 enter value : value entered 65 78 enter value : 65 enter value : value entered 65 12 enter value : 35 enter value : value entered 35 

please guide me in cleaning code expected output.

i suggest use conditional variable such cases.

https://computing.llnl.gov/tutorials/pthreads/#convaroverview

this way more efficient task. consumer should wait cond variable. when producer new data, notify condition variable , consumer wake job data.

the link above has pretty explanation, if have questions, welcome