1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
|
/*
* This file contains the old semaphore code that we need to
* preserve for glibc-2.0 backwards compatibility. Port to glibc 2.1
* done by Cristian Gafton.
*/
/* Linuxthreads - a simple clone()-based implementation of Posix */
/* threads for Linux. */
/* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr) */
/* */
/* This program is free software; you can redistribute it and/or */
/* modify it under the terms of the GNU Library General Public License */
/* as published by the Free Software Foundation; either version 2 */
/* of the License, or (at your option) any later version. */
/* */
/* This program is distributed in the hope that it will be useful, */
/* but WITHOUT ANY WARRANTY; without even the implied warranty of */
/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the */
/* GNU Library General Public License for more details. */
/* Semaphores a la POSIX 1003.1b */
#include <errno.h>
#include "pthread.h"
#include "internals.h"
#include "spinlock.h"
#include "restart.h"
#include "queue.h"
typedef struct {
long int sem_status;
int sem_spinlock;
} old_sem_t;
/* Maximum value the semaphore can have. */
#define SEM_VALUE_MAX ((int) ((~0u) >> 1))
static inline int sem_compare_and_swap(old_sem_t *sem, long oldval, long newval)
{
return compare_and_swap(&sem->sem_status, oldval, newval, &sem->sem_spinlock);
}
/* The state of a semaphore is represented by a long int encoding
either the semaphore count if >= 0 and no thread is waiting on it,
or the head of the list of threads waiting for the semaphore.
To distinguish the two cases, we encode the semaphore count N
as 2N+1, so that it has the lowest bit set.
A sequence of sem_wait operations on a semaphore initialized to N
result in the following successive states:
2N+1, 2N-1, ..., 3, 1, &first_waiting_thread, &second_waiting_thread, ...
*/
static void sem_restart_list(pthread_descr waiting);
int __old_sem_init(old_sem_t *sem, int pshared, unsigned int value)
{
if (value > SEM_VALUE_MAX) {
errno = EINVAL;
return -1;
}
if (pshared) {
errno = ENOSYS;
return -1;
}
sem->sem_spinlock = 0;
sem->sem_status = ((long)value << 1) + 1;
return 0;
}
int __old_sem_wait(old_sem_t * sem)
{
long oldstatus, newstatus;
volatile pthread_descr self = thread_self();
pthread_descr * th;
while (1) {
do {
oldstatus = sem->sem_status;
if ((oldstatus & 1) && (oldstatus != 1))
newstatus = oldstatus - 2;
else {
newstatus = (long) self;
self->p_nextwaiting = (pthread_descr) oldstatus;
}
}
while (! sem_compare_and_swap(sem, oldstatus, newstatus));
if (newstatus & 1)
/* We got the semaphore. */
return 0;
/* Wait for sem_post or cancellation */
suspend_with_cancellation(self);
/* This is a cancellation point */
if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
/* Remove ourselves from the waiting list if we're still on it */
/* First check if we're at the head of the list. */
do {
oldstatus = sem->sem_status;
if (oldstatus != (long) self) break;
newstatus = (long) self->p_nextwaiting;
}
while (! sem_compare_and_swap(sem, oldstatus, newstatus));
/* Now, check if we're somewhere in the list.
There's a race condition with sem_post here, but it does not matter:
the net result is that at the time pthread_exit is called,
self is no longer reachable from sem->sem_status. */
if (oldstatus != (long) self && (oldstatus & 1) == 0) {
for (th = &(((pthread_descr) oldstatus)->p_nextwaiting);
*th != NULL && *th != (pthread_descr) 1;
th = &((*th)->p_nextwaiting)) {
if (*th == self) {
*th = self->p_nextwaiting;
break;
}
}
}
pthread_exit(PTHREAD_CANCELED);
}
}
}
int __old_sem_trywait(old_sem_t * sem)
{
long oldstatus, newstatus;
do {
oldstatus = sem->sem_status;
if ((oldstatus & 1) == 0 || (oldstatus == 1)) {
errno = EAGAIN;
return -1;
}
newstatus = oldstatus - 2;
}
while (! sem_compare_and_swap(sem, oldstatus, newstatus));
return 0;
}
int __old_sem_post(old_sem_t * sem)
{
long oldstatus, newstatus;
do {
oldstatus = sem->sem_status;
if ((oldstatus & 1) == 0)
newstatus = 3;
else {
if (oldstatus >= SEM_VALUE_MAX) {
/* Overflow */
errno = ERANGE;
return -1;
}
newstatus = oldstatus + 2;
}
}
while (! sem_compare_and_swap(sem, oldstatus, newstatus));
if ((oldstatus & 1) == 0)
sem_restart_list((pthread_descr) oldstatus);
return 0;
}
int __old_sem_getvalue(old_sem_t * sem, int * sval)
{
long status = sem->sem_status;
if (status & 1)
*sval = (int)((unsigned long) status >> 1);
else
*sval = 0;
return 0;
}
int __old_sem_destroy(old_sem_t * sem)
{
if ((sem->sem_status & 1) == 0) {
errno = EBUSY;
return -1;
}
return 0;
}
/* Auxiliary function for restarting all threads on a waiting list,
in priority order. */
static void sem_restart_list(pthread_descr waiting)
{
pthread_descr th, towake, *p;
/* Sort list of waiting threads by decreasing priority (insertion sort) */
towake = NULL;
while (waiting != (pthread_descr) 1) {
th = waiting;
waiting = waiting->p_nextwaiting;
p = &towake;
while (*p != NULL && th->p_priority < (*p)->p_priority)
p = &((*p)->p_nextwaiting);
th->p_nextwaiting = *p;
*p = th;
}
/* Wake up threads in priority order */
while (towake != NULL) {
th = towake;
towake = towake->p_nextwaiting;
th->p_nextwaiting = NULL;
restart(th);
}
}
#if defined PIC && DO_VERSIONING
symbol_version (__old_sem_init, sem_init, GLIBC_2.0);
symbol_version (__old_sem_wait, sem_wait, GLIBC_2.0);
symbol_version (__old_sem_trywait, sem_trywait, GLIBC_2.0);
symbol_version (__old_sem_post, sem_post, GLIBC_2.0);
symbol_version (__old_sem_getvalue, sem_getvalue, GLIBC_2.0);
symbol_version (__old_sem_destroy, sem_destroy, GLIBC_2.0);
#endif
|
