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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

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

ERRORS

CONFORMING TO

NOTES

EXAMPLE

If the program is run with no command-line argument, then it passes NULL as the attr argument of pthread_create(3), so that the thread is created with default attributes. Running the program on Linux/x86-32 with the NPTL threading implementation, we see the following:

$ ulimit -s       # No stack imit ==> default stack size is 2MB
unlimited
$ ./a.out
Thread attributes:
        Detach state        = PTHREAD_CREATE_JOINABLE
        Scope               = PTHREAD_SCOPE_SYSTEM
        Inherit scheduler   = PTHREAD_INHERIT_SCHED
        Scheduling policy   = SCHED_OTHER
        Scheduling priority = 0
        Guard size          = 4096 bytes
        Stack address       = 0x40196000
        Stack size          = 0x201000 bytes

When we supply a stack size as a command-line argument, the program initializes a thread attributes object, sets various attributes in that object, and passes a pointer to the object in the call to pthread_create(3). Running the program on Linux/x86-32 with the NPTL threading implementation, we see the following:

$ ./a.out 0x3000000
posix_memalign() allocated at 0x40197000
Thread attributes:
        Detach state        = PTHREAD_CREATE_DETACHED
        Scope               = PTHREAD_SCOPE_SYSTEM
        Inherit scheduler   = PTHREAD_EXPLICIT_SCHED
        Scheduling policy   = SCHED_OTHER
        Scheduling priority = 0
        Guard size          = 0 bytes
        Stack address       = 0x40197000
        Stack size          = 0x3000000 bytes

Program source

#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() */
}

SEE ALSO

COLOPHON

Index

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

CONFORMING TO

NOTES

EXAMPLE

Program source

SEE ALSO

COLOPHON

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