common/resolv/mtctxres.c

/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */


#include <port_before.h>
#ifdef DO_PTHREADS
#include <pthread.h>
#endif
#include <errno.h>
#include <netdb.h>
#include <stdlib.h>
#include <string.h>
#include <resolv_mt.h>
#include <irs.h>
#include <port_after.h>

#ifdef DO_PTHREADS
static pthread_key_t    key;
static int      mt_key_initialized = 0;

static int      __res_init_ctx(void);
static void     __res_destroy_ctx(void *);

#if defined(sun) && !defined(__GNUC__)
#pragma init    (_mtctxres_init)
#endif
#endif

static mtctxres_t   sharedctx;

#ifdef DO_PTHREADS
/*
 * Initialize the TSD key. By doing this at library load time, we're
 * implicitly running without interference from other threads, so there's
 * no need for locking.
 */
static void
_mtctxres_init(void) {
    int pthread_keycreate_ret;

    pthread_keycreate_ret = pthread_key_create(&key, __res_destroy_ctx);
    if (pthread_keycreate_ret == 0)
        mt_key_initialized = 1;
}
#endif

/*
 * To support binaries that used the private MT-safe interface in
 * Solaris 8, we still need to provide the __res_enable_mt()
 * and __res_disable_mt() entry points. They're do-nothing routines.
 */
int
__res_enable_mt(void) {
    return (-1);
}

int
__res_disable_mt(void) {
    return (0);
}

#ifdef DO_PTHREADS
static int
__res_init_ctx(void) {

    mtctxres_t  *mt;
    int     ret;


    if (pthread_getspecific(key) != 0) {
        /* Already exists */
        return (0);
    }

    if ((mt = malloc(sizeof (mtctxres_t))) == 0) {
        errno = ENOMEM;
        return (-1);
    }

    memset(mt, 0, sizeof (mtctxres_t));

    if ((ret = pthread_setspecific(key, mt)) != 0) {
        free(mt);
        errno = ret;
        return (-1);
    }

    return (0);
}

static void
__res_destroy_ctx(void *value) {

    mtctxres_t  *mt = (mtctxres_t *)value;

    if (mt != 0)
        free(mt);
}
#endif

mtctxres_t *
___mtctxres(void) {
#ifdef DO_PTHREADS
    mtctxres_t  *mt;

    /*
     * This if clause should only be executed if we are linking
     * statically.  When linked dynamically _mtctxres_init() should
     * be called at binding time due the #pragma above.
     */
    if (!mt_key_initialized) {
        static pthread_mutex_t keylock = PTHREAD_MUTEX_INITIALIZER;
                if (pthread_mutex_lock(&keylock) == 0) {
            _mtctxres_init();
            (void) pthread_mutex_unlock(&keylock);
        }
    }

    /*
     * If we have already been called in this thread return the existing
     * context.  Otherwise recreat a new context and return it.  If
     * that fails return a global context.
     */
    if (mt_key_initialized) {
        if (((mt = pthread_getspecific(key)) != 0) ||
            (__res_init_ctx() == 0 &&
             (mt = pthread_getspecific(key)) != 0)) {
            return (mt);
        }
    }
#endif
    return (&sharedctx);
}