-
Notifications
You must be signed in to change notification settings - Fork 3
Expand file tree
/
Copy pathrwlock.c
More file actions
199 lines (187 loc) · 4.91 KB
/
rwlock.c
File metadata and controls
199 lines (187 loc) · 4.91 KB
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
/*
* Project: Read-Write Lock for C
* File: rwlock.c
* Author: Jason Papapanagiotakis
* Github: https://github.com/JasonPap/ReadWriteLock
*/
#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include "rwlock.h"
struct ReadWriteLock_s
{
sem_t wrt;
sem_t mtx;
sem_t delFlag;
int readcount;
int active;
};
//typedef struct ReadWriteLock_s* ReadWriteLock;
//forward declaration
/* This function is used to take the state of the lock.
* Return values:
* [*] 1 is returned when the lock is alive.
* [*] 0 is returned when the lock is marked for delete.
* [*] -1 is returned if an error was encountered.
*/
int rwl_isActive(ReadWriteLock);
int rwl_init(ReadWriteLock* lock)
{
(*lock) = malloc(sizeof(struct ReadWriteLock_s));
if ((*lock) == NULL)
{
perror("rwl_init - could not allocate memory for lock\n");
return -1;
}
if (sem_init(&((*lock)->wrt), 0, 1) == -1)
{
perror("rwl_init - could not allocate wrt semaphore\n");
free(*lock);
*lock = NULL;
return -1;
}
if (sem_init(&((*lock)->mtx), 0, 1) == -1)
{
perror("rwl_init - could not allocate mtx semaphore\n");
sem_destroy(&((*lock)->wrt));
free(*lock);
*lock = NULL;
return -1;
}
if (sem_init(&((*lock)->delFlag), 0, 1) == -1)
{
perror("rwl_init - could not allocate delFlag semaphore\n");
sem_destroy(&((*lock)->wrt));
sem_destroy(&((*lock)->mtx));
free(*lock);
*lock = NULL;
return -1;
}
(*lock)->readcount = 0;
(*lock)->active = 1;
return 0;
}
int rwl_destroy(ReadWriteLock* lock)
{
if (lock == NULL) {
perror("rwl_destroy - NULL argument");
return -1;
}
errno = 0;
if (sem_trywait(&((*lock)->wrt)) == -1)
perror("rwl_destroy - trywait on wrt failed.");
if ( errno == EAGAIN)
perror("rwl_destroy - wrt is locked, undefined behaviour.");
errno = 0;
if (sem_trywait(&((*lock)->mtx)) == -1)
perror("rwl_destroy - trywait on mtx failed.");
if ( errno == EAGAIN)
perror("rwl_destroy - mtx is locked, undefined behaviour.");
if (sem_destroy(&((*lock)->wrt)) == -1)
perror("rwl_destroy - destroy wrt failed");
if (sem_destroy(&((*lock)->mtx)) == -1)
perror("rwl_destroy - destroy mtx failed");
if (sem_destroy(&((*lock)->delFlag)) == -1)
perror("rwl_destroy - destroy delFlag failed");
free(*lock);
*lock = NULL;
return 0;
}
int rwl_writeLock(ReadWriteLock lock)
{
if (lock == NULL) {
perror("rwl_writeLock - NULL argument");
return -1;
}
if (sem_wait(&(lock->wrt)) == -1)
{
perror("rwl_writeLock - wait on wrt failed.");
return -1;
}
return 0;
}
int rwl_writeUnlock(ReadWriteLock lock)
{
if (lock == NULL) {
perror("rwl_writeUnlock - NULL argument");
return -1;
}
if (sem_post(&(lock->wrt)) == -1)
{
perror("rwl_writeUnlock - post on wrt failed.");
return -1;
}
return 0;
}
int rwl_readLock(ReadWriteLock lock)
{
if (lock == NULL) {
perror("rwl_readLock - NULL argument");
return -1;
}
if (sem_wait(&(lock->mtx)) == -1)
{
perror("rwl_readLock - wait on mtx failed");
return -1;
}
lock->readcount += 1;
if (lock->readcount == 1)
if (sem_wait(&(lock->wrt)) == -1)
{
perror("rwl_readLock - wait on wrt failed");
sem_post(&(lock->mtx)); //return semaphore to original state
return -1;
}
if (sem_post(&(lock->mtx)) == -1)
{
perror("rwl_readLock - post on mtx failed, undefined behaviour");
return -1;
}
return 0;
}
int rwl_readUnlock(ReadWriteLock lock)
{
if (lock == NULL) {
perror("rwl_readUnlock - NULL argument");
return -1;
}
if (sem_wait(&(lock->mtx)) == -1)
{
perror("rwl_readUnlock - wait on mtx failed");
return -1;
}
lock->readcount -= 1;
if (lock->readcount == 0)
if (sem_post(&(lock->wrt)) == -1)
{
perror("rwl_readUnlock - post on wrt failed");
sem_post(&(lock->mtx)); //return semaphore to original state
return -1;
}
if (sem_post(&(lock->mtx)) == -1)
{
perror("rwl_readUnlock - post on mtx failed, undefined behaviour");
return -1;
}
return 0;
}
int rwl_isActive(ReadWriteLock lock)
{
if (lock == NULL) {
perror("rwl_isActive - NULL argument");
return -1;
}
errno = 0;
if (sem_trywait(&(lock->delFlag)) == -1)
{
perror("rwl_isActive - trywait on delFlag failed.");
return -1;
}
if ( errno == EAGAIN)
{//delFlag is down, lock is marked for delete
perror("rwl_isActive - tried to lock but ReadWriteLock was marked for delete");
return 0;
}
return 1;
}