lib/libc/sysvipc/lock_generic.c

   1 /*-
   2  * Copyright (c) 2005 David Xu <davidxu@freebsd.org>
   3  * Copyright (c) 2005 Matthew Dillon <dillon@backplane.com>
   4  *
   5  * All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  26  * SUCH DAMAGE.
  27  *
  28  * $DragonFly: src/lib/libthread_xu/thread/thr_umtx.c,v 1.4 2008/04/14 20:12:41 dillon Exp $
  29  */
  30
  31 #include <assert.h>
  32 #include <errno.h>
  33 #include <unistd.h>
  34 #include <sys/time.h>
  35
  36 #include "sysvipc_lock_generic.h"
  37
  38 /*
  39  * This function is used to acquire a contested lock.
  40  */
  41 int
  42 __sysv_umtx_lock(volatile umtx_t *mtx, int timo)
  43 {
  44         int v, errval, ret = 0;
  45
  46         /* contested */
  47         do {
  48                 v = *mtx;
  49                 if (v == 2 || atomic_cmpset_acq_int(mtx, 1, 2)) {
  50                         if (timo == 0)
  51                                 umtx_sleep(mtx, 2, timo);
  52                         else if ( (errval = umtx_sleep(mtx, 2, timo)) > 0) {
  53                                 if (errval == EAGAIN) {
  54                                         if (atomic_cmpset_acq_int(mtx, 0, 2))
  55                                                 ret = 0;
  56                                         else
  57                                                 ret = ETIMEDOUT;
  58                                         break;
  59                                 }
  60                         }
  61                 }
  62         } while (!atomic_cmpset_acq_int(mtx, 0, 2));
  63
  64         return (ret);
  65 }
  66
  67 void
  68 __sysv_umtx_unlock(volatile umtx_t *mtx)
  69 {
  70         int v;
  71
  72         for (;;) {
  73                 v = *mtx;
  74                 if (atomic_cmpset_acq_int(mtx, v, v-1)) {
  75                         if (v != 1) {
  76                                 *mtx = 0;
  77                                 umtx_wakeup(mtx, 1);
  78                         }
  79                         break;
  80                 }
  81         }
  82 }