pthread_attr_destroy example c c++

Name

pthread_attr_init, pthread_attr_destroy - initialize and destroy thread attributes object

Synopsis

#include <pthread.h>

int pthread_attr_init(pthread_attr_t *attr);
int pthread_attr_destroy(pthread_attr_t *attr);

Compile and link with -pthread.

Description of (pthread_attr_init, pthread_attr_destroy)

The pthread_attr_init() function initializes the thread attributes object pointed to by attr with default attribute values. After this call, individual attributes of the object can be set using various related functions (listed under SEE ALSO), and then the object can be used in one or more pthread_create(3) calls that create threads.

Calling pthread_attr_init() on a thread attributes object that has already been initialized results in undefined behavior.

When a thread attributes object is no longer required, it should be destroyed using the pthread_attr_destroy() function. Destroying a thread attributes object has no effect on threads that were created using that object.

Once a thread attributes object has been destroyed, it can be reinitialized using pthread_attr_init(). Any other use of a destroyed thread attributes object has undefined results.

Return Value - (pthread_attr_init, pthread_attr_destroy)

On success, these functions return 0; on error, they return a nonzero error number.

Errors

POSIX.1-2001 documents an ENOMEM error for pthread_attr_init(); on Linux these functions always succeed (but portable and future-proof applications should nevertheless handle a possible error return).(pthread_attr_init, pthread_attr_destroy)

Conforming To

POSIX.1-2001.

Notes

The pthread_attr_t type should be treated as opaque: any access to the object other than via pthreads functions is nonportable and produces undefined results.


Example of (pthread_attr_init, pthread_attr_destroy)

#define _GNU_SOURCE     /* To get pthread_getattr_np() declaration */
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

#define handle_error_en(en, msg) \
        do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

static void
display_pthread_attr(pthread_attr_t *attr, char *prefix)
{
    int s, i;
    size_t v;
    void *stkaddr;
    struct sched_param sp;

   s = pthread_attr_getdetachstate(attr, &i);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getdetachstate");
    printf("%sDetach state        = %s\n", prefix,
            (i == PTHREAD_CREATE_DETACHED) ? "PTHREAD_CREATE_DETACHED" :
            (i == PTHREAD_CREATE_JOINABLE) ? "PTHREAD_CREATE_JOINABLE" :
            "???");

   s = pthread_attr_getscope(attr, &i);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getscope");
    printf("%sScope               = %s\n", prefix,
            (i == PTHREAD_SCOPE_SYSTEM)  ? "PTHREAD_SCOPE_SYSTEM" :
            (i == PTHREAD_SCOPE_PROCESS) ? "PTHREAD_SCOPE_PROCESS" :
            "???");

   s = pthread_attr_getinheritsched(attr, &i);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getinheritsched");
    printf("%sInherit scheduler   = %s\n", prefix,
            (i == PTHREAD_INHERIT_SCHED)  ? "PTHREAD_INHERIT_SCHED" :
            (i == PTHREAD_EXPLICIT_SCHED) ? "PTHREAD_EXPLICIT_SCHED" :
            "???");

   s = pthread_attr_getschedpolicy(attr, &i);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getschedpolicy");
    printf("%sScheduling policy   = %s\n", prefix,
            (i == SCHED_OTHER) ? "SCHED_OTHER" :
            (i == SCHED_FIFO)  ? "SCHED_FIFO" :
            (i == SCHED_RR)    ? "SCHED_RR" :
            "???");

   s = pthread_attr_getschedparam(attr, &sp);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getschedparam");
    printf("%sScheduling priority = %d\n", prefix, sp.sched_priority);

   s = pthread_attr_getguardsize(attr, &v);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getguardsize");
    printf("%sGuard size          = %d bytes\n", prefix, v);

   s = pthread_attr_getstack(attr, &stkaddr, &v);
    if (s != 0)
        handle_error_en(s, "pthread_attr_getstack");
    printf("%sStack address       = %p\n", prefix, stkaddr);
    printf("%sStack size          = 0x%x bytes\n", prefix, v);
}

static void *
thread_start(void *arg)
{
    int s;
    pthread_attr_t gattr;

   /* pthread_getattr_np() is a non-standard GNU extension that
       retrieves the attributes of the thread specified in its
       first argument */

   s = pthread_getattr_np(pthread_self(), &gattr);
    if (s != 0)
        handle_error_en(s, "pthread_getattr_np");

   printf("Thread attributes:\n");
    display_pthread_attr(&gattr, "\t");

   exit(EXIT_SUCCESS);         /* Terminate all threads */
}

int
main(int argc, char *argv[])
{
    pthread_t thr;
    pthread_attr_t attr;
    pthread_attr_t *attrp;      /* NULL or &attr */
    int s;

   attrp = NULL;

   /* If a command-line argument was supplied, use it to set the
       stack-size attribute and set a few other thread attributes,
       and set attrp pointing to thread attributes object */

   if (argc > 1) {
        int stack_size;
        void *sp;

       attrp = &attr;

       s = pthread_attr_init(&attr);
        if (s != 0)
            handle_error_en(s, "pthread_attr_init");

       s = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
        if (s != 0)
            handle_error_en(s, "pthread_attr_setdetachstate");

       s = pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED);
        if (s != 0)
            handle_error_en(s, "pthread_attr_setinheritsched");

       stack_size = strtoul(argv[1], NULL, 0);

       s = posix_memalign(&sp, sysconf(_SC_PAGESIZE), stack_size);
        if (s != 0)
            handle_error_en(s, "posix_memalign");

       printf("posix_memalign() allocated at %p\n", sp);

       s = pthread_attr_setstack(&attr, sp, stack_size);
        if (s != 0)
            handle_error_en(s, "pthread_attr_setstack");
    }

   s = pthread_create(&thr, attrp, &thread_start, NULL);
    if (s != 0)
        handle_error_en(s, "pthread_create");

   if (attrp != NULL) {
        s = pthread_attr_destroy(attrp);
        if (s != 0)
            handle_error_en(s, "pthread_attr_destroy");
    }

   pause();    /* Terminates when other thread calls exit() */
}