1 /* sem_wait -- wait on a semaphore.  Generic futex-using version.
2    Copyright (C) 2003, 2007 Free Software Foundation, Inc.
3    This file is part of the GNU C Library.
4    Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
5 
6    The GNU C Library is free software; you can redistribute it and/or
7    modify it under the terms of the GNU Lesser General Public
8    License as published by the Free Software Foundation; either
9    version 2.1 of the License, or (at your option) any later version.
10 
11    The GNU C Library is distributed in the hope that it will be useful,
12    but WITHOUT ANY WARRANTY; without even the implied warranty of
13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
14    Lesser General Public License for more details.
15 
16    You should have received a copy of the GNU Lesser General Public
17    License along with the GNU C Library; if not, see
18    <http://www.gnu.org/licenses/>.  */
19 
20 #include <errno.h>
21 #include <sysdep.h>
22 #include <lowlevellock.h>
23 #include <internaltypes.h>
24 #include <semaphore.h>
25 
26 #include <pthreadP.h>
27 
28 
29 void
30 attribute_hidden
__sem_wait_cleanup(void * arg)31 __sem_wait_cleanup (void *arg)
32 {
33   struct new_sem *isem = (struct new_sem *) arg;
34 
35   atomic_decrement (&isem->nwaiters);
36 }
37 
38 
39 int
sem_wait(sem_t * sem)40 sem_wait (sem_t *sem)
41 {
42   struct new_sem *isem = (struct new_sem *) sem;
43   int err;
44 
45   if (atomic_decrement_if_positive (&isem->value) > 0)
46     return 0;
47 
48   atomic_increment (&isem->nwaiters);
49 
50   pthread_cleanup_push (__sem_wait_cleanup, isem);
51 
52   while (1)
53     {
54       /* Enable asynchronous cancellation.  Required by the standard.  */
55       int oldtype = __pthread_enable_asynccancel ();
56 
57       err = lll_futex_wait (&isem->value, 0,
58 			    isem->private ^ FUTEX_PRIVATE_FLAG);
59 
60       /* Disable asynchronous cancellation.  */
61       __pthread_disable_asynccancel (oldtype);
62 
63       if (err != 0 && err != -EWOULDBLOCK)
64 	{
65 	  __set_errno (-err);
66 	  err = -1;
67 	  break;
68 	}
69 
70       if (atomic_decrement_if_positive (&isem->value) > 0)
71 	{
72 	  err = 0;
73 	  break;
74 	}
75     }
76 
77   pthread_cleanup_pop (0);
78 
79   atomic_decrement (&isem->nwaiters);
80 
81   return err;
82 }
83