POSIX

PThreads

General Information

Links:

• POSIX Threads Programming, excellent introduction to pthreads, by Blaise Barney, at Lawrence Livermore National Laboratory.
• Advanced Linux Programming Ch 4 — Threads
• POSIX thread (pthread) libraries
• POSIX Threads (wikipedia)

Manual page:

• pthreads (7)

Portability

Joinable / detachable state

For portability, always create joinable or detachable threads by setting explicitly the thread attribute (using pthread_attr_getdetachstate). This provides portability as not all implementations may create threads as joinable by default.

Thread-Local Data

• Using thread-specific data area foreseen by POSIX, which requires first creating a key that is later used to set or get thread-specific data attached to that key (see Advanced Linux Programming - Ch 4)
• Using keyword __thread, see http://www.akkadia.org/drepper/tls.pdf (not available in all compiler, not standard C99 [1]).

// Compile this code with : gcc local.c -o local -lpthread

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

static __thread int myint;
static int globalint = 0;

void * handler(void *arg)
{
    myint = ++globalint;                              // thread unsafe - should use a mutex
    while(1) {
        printf("myint is %d\n", myint);
        sleep(1);
    }
}

int main (int argc, char **argv)
{
    pthread_t p1,p2;

    pthread_create(&p1, NULL, handler, NULL);
    pthread_create(&p2, NULL, handler, NULL);

    pause();
    return 0;
}

Debugging

See Debugging page.