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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_stack_related_attributes(pthread_attr_t *attr, char *prefix)
{


    int s;


    size_t stack_size, guard_size;


    void *stack_addr;


    s = pthread_attr_getguardsize(attr, &guard_size);


    if (s != 0)


        errc(EXIT_FAILURE, s, "pthread_attr_getguardsize");


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


    s = pthread_attr_getstack(attr, &stack_addr, &stack_size);


    if (s != 0)


        errc(EXIT_FAILURE, s, "pthread_attr_getstack");


    printf("%sStack address       = %p", prefix, stack_addr);


    if (stack_size > 0)


        printf(" (EOS = %p)", (char *) stack_addr + stack_size);


    printf("\n");


    printf("%sStack size          = %#zx (%zu) bytes\n",


           prefix, stack_size, stack_size);
}
static void
display_thread_attributes(pthread_t thread, char *prefix)
{


    int s;


    pthread_attr_t attr;


    s = pthread_getattr_np(thread, &attr);


    if (s != 0)


        errc(EXIT_FAILURE, s, "pthread_getattr_np");


    display_stack_related_attributes(&attr, prefix);


    s = pthread_attr_destroy(&attr);


    if (s != 0)


        errc(EXIT_FAILURE, s, "pthread_attr_destroy");
}
static void *           /* Start function for thread we create */
thread_start(void *arg)
{


    printf("Attributes of created thread:\n");


    display_thread_attributes(pthread_self(), "\t");


    exit(EXIT_SUCCESS);         /* Terminate all threads */
}
static void
usage(char *pname, char *msg)
{


    if (msg != NULL)


        fputs(msg, stderr);


    fprintf(stderr, "Usage: %s [-s stack-size [-a]]"


            " [-g guard-size]\n", pname);


    fprintf(stderr, "\t\t-a means program should allocate stack\n");


    exit(EXIT_FAILURE);
}
static pthread_attr_t *   /* Get thread attributes from command line */
get_thread_attributes_from_cl(int argc, char *argv[],


                              pthread_attr_t *attrp)
{


    int s, opt, allocate_stack;


    size_t stack_size, guard_size;


    void *stack_addr;


    pthread_attr_t *ret_attrp = NULL;   /* Set to attrp if we initialize


                                           a thread attributes object */


    allocate_stack = 0;


    stack_size = -1;


    guard_size = -1;


    while ((opt = getopt(argc, argv, "ag:s:")) != -1) {


        switch (opt) {


        case 'a':   allocate_stack = 1;                     break;


        case 'g':   guard_size = strtoul(optarg, NULL, 0);  break;


        case 's':   stack_size = strtoul(optarg, NULL, 0);  break;


        default:    usage(argv[0], NULL);


        }


    }


    if (allocate_stack && stack_size == -1)


        usage(argv[0], "Specifying -a without -s makes no sense\n");


    if (argc > optind)


        usage(argv[0], "Extraneous command-line arguments\n");


    if (stack_size != -1 || guard_size > 0) {


        ret_attrp = attrp;


        s = pthread_attr_init(attrp);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_init");


    }


    if (stack_size != -1) {


        if (!allocate_stack) {


            s = pthread_attr_setstacksize(attrp, stack_size);


            if (s != 0)


                errc(EXIT_FAILURE, s, "pthread_attr_setstacksize");


        } else {


            s = posix_memalign(&stack_addr, sysconf(_SC_PAGESIZE),


                               stack_size);


            if (s != 0)


                errc(EXIT_FAILURE, s, "posix_memalign");


            printf("Allocated thread stack at %p\n\n", stack_addr);


            s = pthread_attr_setstack(attrp, stack_addr, stack_size);


            if (s != 0)


                errc(EXIT_FAILURE, s, "pthread_attr_setstacksize");


        }


    }


    if (guard_size != -1) {


        s = pthread_attr_setguardsize(attrp, guard_size);


        if (s != 0)


            errc(EXIT_FAILURE, s, "pthread_attr_setstacksize");


    }


    return ret_attrp;
}
int
main(int argc, char *argv[])
{


    int s;


    pthread_t thr;


    pthread_attr_t attr;


    pthread_attr_t *attrp = NULL;    /* Set to &attr if we initialize


                                        a thread attributes object */


    attrp = get_thread_attributes_from_cl(argc, argv, &attr);


    if (attrp != NULL) {


        printf("Thread attributes object after initializations:\n");


        display_stack_related_attributes(attrp, "\t");


        printf("\n");


    }


    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() */
}