CODEWITHSUNDEEP
clinuxmultithreadingdebian
khernik
khernik

Reputation: 2091

Ordering the execution of two threads

I wanna write two threads, first will read a string from the console, and the second will output the number of characters in it.

To do so, I have to set the order of executing the threads, reading first, writing second.

Also I want one thread to execute at the time.

How can I do this?

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

void *printCharacterNumber(void *ptr);
void *readMessage(void *ptr);

int main()
{
   pthread_t thread1, thread2;
   int iret1, iret2;

   iret1 = pthread_create(&thread1, NULL, printMessage, NULL);
   iret2 = pthread_create(&thread2, NULL, printCharacterNumber, NULL);

   pthread_join(thread1, NULL);
   pthread_join(thread2, NULL);

   return 0;
}

void *readMessage(void *ptr)
{
   char *message;
   fscan("%s", &message);
}

void *printCharacterNumber(void *ptr)
{
   printf("%s", message); // I'll add counting when it will work
}

Upvotes: 0

Views: 96

Answers (1)

Basile Starynkevitch
Basile Starynkevitch

Reputation: 1

The biggest interest of genine (pthread) threads is to enable parallel execution (taking profit of the several cores most laptops and desktops have)... Read some pthread tutorial ...

You may want to use barriers. Read more about pthread_barrier_wait & pthread_barrier_init

If you want to serialize some counter, you could use (with recent C11 compilers, e.g. GCC 4.9) some atomic builtins, or more usually a mutex, see pthread_mutex_init & pthread_mutex_lock etc....:

 static pthread_mutex_t mtx = PTHREAD_MUTEX_INIT;

 static long counter;

 void increment_serialized_counter (void) {
     pthread_mutex_lock(&mtx);
     counter++;
     pthread_mutex_unclock(&mtx);
 }

 long get_serialized_counter (void) {
    long r = 0;
    pthread_mutex_lock(&mtx);
    r = counter;
    pthread_mutex_unclock(&mtx);
    return r;
 }

You probably should use a mutex for your message variable, if it was static!

Upvotes: 1

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