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


        errc(EXIT_FAILURE, 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)


        errc(EXIT_FAILURE, 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)


        errc(EXIT_FAILURE, 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)


        errc(EXIT_FAILURE, 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)


        errc(EXIT_FAILURE, s, "pthread_attr_getschedparam");


    printf("%sScheduling priority = %d\n", prefix, sp.sched_priority);


    s = pthread_attr_getguardsize(attr, &v);


    if (s != 0)


        errc(EXIT_FAILURE, s, "pthread_attr_getguardsize");


    printf("%sGuard size          = %zu bytes\n", prefix, v);


    s = pthread_attr_getstack(attr, &stkaddr, &v);


    if (s != 0)


        errc(EXIT_FAILURE, s, "pthread_attr_getstack");


    printf("%sStack address       = %p\n", prefix, stkaddr);


    printf("%sStack size          = %#zx 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)


        errc(EXIT_FAILURE, 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) {


        size_t stack_size;


        void *sp;


        attrp = &attr;


        s = pthread_attr_init(&attr);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_init");


        s = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_setdetachstate");


        s = pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_setinheritsched");


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


        s = posix_memalign(&sp, sysconf(_SC_PAGESIZE), stack_size);


        if (s != 0)


            errc(EXIT_FAILURE, s, "posix_memalign");


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


        s = pthread_attr_setstack(&attr, sp, stack_size);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_setstack");


    }


    s = pthread_create(&thr, attrp, &thread_start, NULL);


    if (s != 0)


        errc(EXIT_FAILURE, s, "pthread_create");


    if (attrp != NULL) {


        s = pthread_attr_destroy(attrp);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_destroy");


    }


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