Adjusted.
[glibc.git] / linuxthreads / oldsemaphore.c
blob2099b8bbdadb96dfc77d99ab91815fe06641a64d
1 /*
2 * This file contains the old semaphore code that we need to
3 * preserve for glibc-2.0 backwards compatibility. Port to glibc 2.1
4 * done by Cristian Gafton.
5 */
7 /* Linuxthreads - a simple clone()-based implementation of Posix */
8 /* threads for Linux. */
9 /* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr) */
10 /* */
11 /* This program is free software; you can redistribute it and/or */
12 /* modify it under the terms of the GNU Library General Public License */
13 /* as published by the Free Software Foundation; either version 2 */
14 /* of the License, or (at your option) any later version. */
15 /* */
16 /* This program is distributed in the hope that it will be useful, */
17 /* but WITHOUT ANY WARRANTY; without even the implied warranty of */
18 /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the */
19 /* GNU Library General Public License for more details. */
21 /* Semaphores a la POSIX 1003.1b */
22 #include <shlib-compat.h>
23 #if SHLIB_COMPAT(libpthread, GLIBC_2_0, GLIBC_2_1)
25 #include <errno.h>
26 #include "pthread.h"
27 #include "internals.h"
28 #include "spinlock.h"
29 #include "restart.h"
30 #include "queue.h"
32 typedef struct {
33 long int sem_status;
34 int sem_spinlock;
35 } old_sem_t;
37 extern int __old_sem_init (old_sem_t *__sem, int __pshared, unsigned int __value);
38 extern int __old_sem_wait (old_sem_t *__sem);
39 extern int __old_sem_trywait (old_sem_t *__sem);
40 extern int __old_sem_post (old_sem_t *__sem);
41 extern int __old_sem_getvalue (old_sem_t *__sem, int *__sval);
42 extern int __old_sem_destroy (old_sem_t *__sem);
45 /* Maximum value the semaphore can have. */
46 #define SEM_VALUE_MAX ((int) ((~0u) >> 1))
48 static inline int sem_compare_and_swap(old_sem_t *sem, long oldval, long newval)
50 return compare_and_swap(&sem->sem_status, oldval, newval, &sem->sem_spinlock);
53 /* The state of a semaphore is represented by a long int encoding
54 either the semaphore count if >= 0 and no thread is waiting on it,
55 or the head of the list of threads waiting for the semaphore.
56 To distinguish the two cases, we encode the semaphore count N
57 as 2N+1, so that it has the lowest bit set.
59 A sequence of sem_wait operations on a semaphore initialized to N
60 result in the following successive states:
61 2N+1, 2N-1, ..., 3, 1, &first_waiting_thread, &second_waiting_thread, ...
64 static void sem_restart_list(pthread_descr waiting);
66 int __old_sem_init(old_sem_t *sem, int pshared, unsigned int value)
68 if (value > SEM_VALUE_MAX) {
69 errno = EINVAL;
70 return -1;
72 if (pshared) {
73 errno = ENOSYS;
74 return -1;
76 sem->sem_spinlock = __LT_SPINLOCK_INIT;
77 sem->sem_status = ((long)value << 1) + 1;
78 return 0;
81 /* Function called by pthread_cancel to remove the thread from
82 waiting inside __old_sem_wait. Here we simply unconditionally
83 indicate that the thread is to be woken, by returning 1. */
85 static int old_sem_extricate_func(void *obj, pthread_descr th)
87 return 1;
90 int __old_sem_wait(old_sem_t * sem)
92 long oldstatus, newstatus;
93 volatile pthread_descr self = thread_self();
94 pthread_descr * th;
95 pthread_extricate_if extr;
97 /* Set up extrication interface */
98 extr.pu_object = 0;
99 extr.pu_extricate_func = old_sem_extricate_func;
101 while (1) {
102 /* Register extrication interface */
103 __pthread_set_own_extricate_if(self, &extr);
104 do {
105 oldstatus = sem->sem_status;
106 if ((oldstatus & 1) && (oldstatus != 1))
107 newstatus = oldstatus - 2;
108 else {
109 newstatus = (long) self;
110 self->p_nextwaiting = (pthread_descr) oldstatus;
113 while (! sem_compare_and_swap(sem, oldstatus, newstatus));
114 if (newstatus & 1) {
115 /* We got the semaphore. */
116 __pthread_set_own_extricate_if(self, 0);
117 return 0;
119 /* Wait for sem_post or cancellation */
120 suspend(self);
121 __pthread_set_own_extricate_if(self, 0);
123 /* This is a cancellation point */
124 if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
125 /* Remove ourselves from the waiting list if we're still on it */
126 /* First check if we're at the head of the list. */
127 do {
128 oldstatus = sem->sem_status;
129 if (oldstatus != (long) self) break;
130 newstatus = (long) self->p_nextwaiting;
132 while (! sem_compare_and_swap(sem, oldstatus, newstatus));
133 /* Now, check if we're somewhere in the list.
134 There's a race condition with sem_post here, but it does not matter:
135 the net result is that at the time pthread_exit is called,
136 self is no longer reachable from sem->sem_status. */
137 if (oldstatus != (long) self && (oldstatus & 1) == 0) {
138 for (th = &(((pthread_descr) oldstatus)->p_nextwaiting);
139 *th != NULL && *th != (pthread_descr) 1;
140 th = &((*th)->p_nextwaiting)) {
141 if (*th == self) {
142 *th = self->p_nextwaiting;
143 break;
147 __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
152 int __old_sem_trywait(old_sem_t * sem)
154 long oldstatus, newstatus;
156 do {
157 oldstatus = sem->sem_status;
158 if ((oldstatus & 1) == 0 || (oldstatus == 1)) {
159 errno = EAGAIN;
160 return -1;
162 newstatus = oldstatus - 2;
164 while (! sem_compare_and_swap(sem, oldstatus, newstatus));
165 return 0;
168 int __old_sem_post(old_sem_t * sem)
170 long oldstatus, newstatus;
172 do {
173 oldstatus = sem->sem_status;
174 if ((oldstatus & 1) == 0)
175 newstatus = 3;
176 else {
177 if (oldstatus >= SEM_VALUE_MAX) {
178 /* Overflow */
179 errno = ERANGE;
180 return -1;
182 newstatus = oldstatus + 2;
185 while (! sem_compare_and_swap(sem, oldstatus, newstatus));
186 if ((oldstatus & 1) == 0)
187 sem_restart_list((pthread_descr) oldstatus);
188 return 0;
191 int __old_sem_getvalue(old_sem_t * sem, int * sval)
193 long status = sem->sem_status;
194 if (status & 1)
195 *sval = (int)((unsigned long) status >> 1);
196 else
197 *sval = 0;
198 return 0;
201 int __old_sem_destroy(old_sem_t * sem)
203 if ((sem->sem_status & 1) == 0) {
204 errno = EBUSY;
205 return -1;
207 return 0;
210 /* Auxiliary function for restarting all threads on a waiting list,
211 in priority order. */
213 static void sem_restart_list(pthread_descr waiting)
215 pthread_descr th, towake, *p;
217 /* Sort list of waiting threads by decreasing priority (insertion sort) */
218 towake = NULL;
219 while (waiting != (pthread_descr) 1) {
220 th = waiting;
221 waiting = waiting->p_nextwaiting;
222 p = &towake;
223 while (*p != NULL && th->p_priority < (*p)->p_priority)
224 p = &((*p)->p_nextwaiting);
225 th->p_nextwaiting = *p;
226 *p = th;
228 /* Wake up threads in priority order */
229 while (towake != NULL) {
230 th = towake;
231 towake = towake->p_nextwaiting;
232 th->p_nextwaiting = NULL;
233 restart(th);
237 compat_symbol (libpthread, __old_sem_init, sem_init, GLIBC_2_0);
238 compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
239 compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
240 compat_symbol (libpthread, __old_sem_post, sem_post, GLIBC_2_0);
241 compat_symbol (libpthread, __old_sem_getvalue, sem_getvalue, GLIBC_2_0);
242 compat_symbol (libpthread, __old_sem_destroy, sem_destroy, GLIBC_2_0);
244 #endif