1 /* Read-write lock implementation.
2 Copyright (C) 1998 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Xavier Leroy <Xavier.Leroy@inria.fr>
5 and Ulrich Drepper <drepper@cygnus.com>, 1998.
7 The GNU C Library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Library General Public License as
9 published by the Free Software Foundation; either version 2 of the
10 License, or (at your option) any later version.
12 The GNU C Library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Library General Public License for more details.
17 You should have received a copy of the GNU Library General Public
18 License along with the GNU C Library; see the file COPYING.LIB. If not,
19 write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
20 Boston, MA 02111-1307, USA. */
24 #include "internals.h"
30 pthread_rwlock_init (pthread_rwlock_t
*rwlock
,
31 const pthread_rwlockattr_t
*attr
)
33 rwlock
->rw_spinlock
= 0;
34 rwlock
->rw_readers
= 0;
35 rwlock
->rw_writer
= NULL
;
37 queue_init(&rwlock
->rw_read_waiting
);
38 queue_init(&rwlock
->rw_write_waiting
);
42 rwlock
->rw_kind
= PTHREAD_RWLOCK_DEFAULT_NP
;
43 rwlock
->rw_pshared
= PTHREAD_PROCESS_PRIVATE
;
47 rwlock
->rw_kind
= attr
->lockkind
;
48 rwlock
->rw_pshared
= attr
->pshared
;
56 pthread_rwlock_destroy (pthread_rwlock_t
*rwlock
)
59 _pthread_descr writer
;
61 acquire (&rwlock
->rw_spinlock
);
62 readers
= rwlock
->rw_readers
;
63 writer
= rwlock
->rw_writer
;
64 release (&rwlock
->rw_spinlock
);
66 if (readers
> 0 || writer
!= NULL
)
74 pthread_rwlock_rdlock (pthread_rwlock_t
*rwlock
)
80 acquire (&rwlock
->rw_spinlock
);
81 if (rwlock
->rw_writer
== NULL
82 || (rwlock
->rw_kind
== PTHREAD_RWLOCK_PREFER_READER_NP
83 && rwlock
->rw_readers
!= 0))
84 /* We can add a reader lock. */
87 /* Suspend ourselves, then try again */
88 self
= thread_self ();
89 enqueue (&rwlock
->rw_read_waiting
, self
);
90 release (&rwlock
->rw_spinlock
);
91 suspend (self
); /* This is not a cancellation point */
95 release (&rwlock
->rw_spinlock
);
102 pthread_rwlock_tryrdlock (pthread_rwlock_t
*rwlock
)
106 acquire (&rwlock
->rw_spinlock
);
107 if (rwlock
->rw_writer
== NULL
108 || (rwlock
->rw_kind
== PTHREAD_RWLOCK_PREFER_READER_NP
109 && rwlock
->rw_readers
!= 0))
111 ++rwlock
->rw_readers
;
114 release (&rwlock
->rw_spinlock
);
121 pthread_rwlock_wrlock (pthread_rwlock_t
*rwlock
)
123 pthread_descr self
= thread_self ();
127 acquire (&rwlock
->rw_spinlock
);
128 if (rwlock
->rw_readers
== 0 && rwlock
->rw_writer
== NULL
)
130 rwlock
->rw_writer
= self
;
131 release (&rwlock
->rw_spinlock
);
135 /* Suspend ourselves, then try again */
136 enqueue (&rwlock
->rw_write_waiting
, self
);
137 release (&rwlock
->rw_spinlock
);
138 suspend (self
); /* This is not a cancellation point */
144 pthread_rwlock_trywrlock (pthread_rwlock_t
*rwlock
)
148 acquire (&rwlock
->rw_spinlock
);
149 if (rwlock
->rw_readers
== 0 && rwlock
->rw_writer
== NULL
)
151 rwlock
->rw_writer
= thread_self ();
154 release (&rwlock
->rw_spinlock
);
161 pthread_rwlock_unlock (pthread_rwlock_t
*rwlock
)
163 struct _pthread_queue torestart
;
166 acquire (&rwlock
->rw_spinlock
);
167 if (rwlock
->rw_writer
!= NULL
)
169 /* Unlocking a write lock. */
170 if (rwlock
->rw_writer
!= thread_self ())
172 release (&rwlock
->rw_spinlock
);
175 rwlock
->rw_writer
= NULL
;
177 if (rwlock
->rw_kind
== PTHREAD_RWLOCK_PREFER_READER_NP
178 || (th
= dequeue (&rwlock
->rw_write_waiting
)) == NULL
)
180 /* Restart all waiting readers. */
181 torestart
= rwlock
->rw_read_waiting
;
182 queue_init (&rwlock
->rw_read_waiting
);
183 release (&rwlock
->rw_spinlock
);
184 while ((th
= dequeue (&torestart
)) != NULL
)
189 /* Restart one waiting writer. */
190 release (&rwlock
->rw_spinlock
);
196 /* Unlocking a read lock. */
197 if (rwlock
->rw_readers
== 0)
199 release (&rwlock
->rw_spinlock
);
203 --rwlock
->rw_readers
;
204 if (rwlock
->rw_readers
== 0)
205 /* Restart one waiting writer, if any. */
206 th
= dequeue (&rwlock
->rw_write_waiting
);
210 release (&rwlock
->rw_spinlock
);
221 pthread_rwlockattr_init (pthread_rwlockattr_t
*attr
)
231 pthread_rwlockattr_destroy (pthread_rwlockattr_t
*attr
)
238 pthread_rwlockattr_getpshared (const pthread_rwlockattr_t
*attr
, int *pshared
)
240 *pshared
= attr
->pshared
;
246 pthread_rwlockattr_setpshared (pthread_rwlockattr_t
*attr
, int pshared
)
248 if (pshared
!= PTHREAD_PROCESS_PRIVATE
&& pshared
!= PTHREAD_PROCESS_SHARED
)
251 attr
->pshared
= pshared
;
258 pthread_rwlockattr_getkind_np (const pthread_rwlockattr_t
*attr
, int *pref
)
260 *pref
= attr
->lockkind
;
266 pthread_rwlockattr_setkind_np (pthread_rwlockattr_t
*attr
, int pref
)
268 if (pref
!= PTHREAD_RWLOCK_PREFER_READER_NP
269 && pref
!= PTHREAD_RWLOCK_PREFER_WRITER_NP
270 && pref
!= PTHREAD_RWLOCK_DEFAULT_NP
)
273 attr
->lockkind
= pref
;