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res_state.c revision 1.2 
      1 /*	$NetBSD: res_state.c,v 1.2 2004/05/22 15:44:26 christos Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2004 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Christos Zoulas.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  * 3. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *        This product includes software developed by the NetBSD
     21  *        Foundation, Inc. and its contributors.
     22  * 4. Neither the name of The NetBSD Foundation nor the names of its
     23  *    contributors may be used to endorse or promote products derived
     24  *    from this software without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     27  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     28  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     29  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     30  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     31  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     32  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     33  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     34  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     35  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     36  * POSSIBILITY OF SUCH DAMAGE.
     37  */
     38 
     39 #include <sys/cdefs.h>
     40 #if defined(LIBC_SCCS) && !defined(lint)
     41 __RCSID("$NetBSD: res_state.c,v 1.2 2004/05/22 15:44:26 christos Exp $");
     42 #endif
     43 
     44 #include <sys/types.h>
     45 #include <sys/queue.h>
     46 #include <arpa/inet.h>
     47 #include <arpa/nameser.h>
     48 #include <stdlib.h>
     49 #include <unistd.h>
     50 #include <resolv.h>
     51 
     52 #include "pthread.h"
     53 #include "pthread_int.h"
     54 
     55 #define	MY_LIST_HEAD(name, type)					\
     56 struct name {								\
     57 	union type *lh_first;	/* first element */			\
     58 }
     59 
     60 #define	MY_LIST_ENTRY(type)						\
     61 struct {								\
     62 	union type *le_next;	/* next element */			\
     63 	union type **le_prev;	/* address of previous next element */	\
     64 }
     65 
     66 static MY_LIST_HEAD(, _res_st) res_list = LIST_HEAD_INITIALIZER(&res_list);
     67 
     68 union _res_st {
     69 	MY_LIST_ENTRY(_res_st)	st_list;
     70 	struct __res_state	st_res;
     71 };
     72 
     73 static pthread_mutex_t res_mtx = PTHREAD_MUTEX_INITIALIZER;
     74 
     75 res_state __res_state(void);
     76 res_state __res_get_state(void);
     77 void __res_put_state(res_state);
     78 
     79 #ifdef RES_STATE_DEBUG
     80 static void
     81 res_state_debug(const char *msg, void *p)
     82 {
     83 	char buf[512];
     84 	pthread_t self = pthread_self();
     85 	int len = snprintf(buf, sizeof(buf), "%p: %s %p\n", self, msg, p);
     86 
     87 	(void)write(STDOUT_FILENO, buf, (size_t)len);
     88 }
     89 #else
     90 #define res_state_debug(a, b)
     91 #endif
     92 
     93 
     94 res_state
     95 __res_get_state(void)
     96 {
     97 	res_state res;
     98 	union _res_st *st;
     99 	pthread_mutex_lock(&res_mtx);
    100 	st = LIST_FIRST(&res_list);
    101 	if (st != NULL) {
    102 		res_state_debug("checkout from list", st);
    103 		LIST_REMOVE(st, st_list);
    104 		res_ninit(res = &st->st_res);
    105 	} else {
    106 		res = (res_state)calloc(sizeof(union _res_st), 1);
    107 		res_state_debug("alloc new", res);
    108 	}
    109 	pthread_mutex_unlock(&res_mtx);
    110 	return res;
    111 }
    112 
    113 void
    114 /*ARGSUSED*/
    115 __res_put_state(res_state res)
    116 {
    117 	pthread_mutex_lock(&res_mtx);
    118 	res_state_debug("free", res);
    119 	LIST_INSERT_HEAD(&res_list, (union _res_st *)(void *)res, st_list);
    120 	pthread_mutex_unlock(&res_mtx);
    121 }
    122 
    123 /*
    124  * This is aliased via a macro to _res; don't allow multi-threaded programs
    125  * to use it.
    126  */
    127 res_state
    128 __res_state(void)
    129 {
    130 	static const char res[] = "_res is not supported for multi-threaded"
    131 	    " programs.\n";
    132 	(void)write(STDERR_FILENO, res, sizeof(res) - 1);
    133 	abort();
    134 	return NULL;
    135 }
    136