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
|
/*
* Copyright (C) 2008 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/* implement flockfile(), ftrylockfile() and funlockfile()
*
* we can't use the OpenBSD implementation which uses kernel-specific
* APIs not available on Linux.
*
* Ideally, this would be trivially implemented by adding a
* pthread_mutex_t field to struct __sFILE as defined in
* <stdio.h>.
*
* However, since we don't want to bring pthread into the mix
* as well as change the size of a public API/ABI structure,
* we're going to store the data out-of-band.
*
* we use a hash-table to map FILE* pointers to recursive mutexes
* fclose() will call __fremovelock() defined below to remove
* a pointer from the table.
*
* the behaviour, if fclose() is called while the corresponding
* file is locked is totally undefined.
*/
#include <stdio.h>
#include <pthread.h>
#include <string.h>
/* a node in the hash table */
typedef struct FileLock {
struct FileLock* next;
FILE* file;
pthread_mutex_t mutex;
} FileLock;
/* use a static hash table. We assume that we're not going to
* lock a really large number of FILE* objects on an embedded
* system.
*/
#define FILE_LOCK_BUCKETS 32
typedef struct {
pthread_mutex_t lock;
FileLock* buckets[ FILE_LOCK_BUCKETS ];
} LockTable;
static LockTable* _lockTable;
static pthread_once_t _lockTable_once = PTHREAD_ONCE_INIT;
static void
lock_table_init( void )
{
_lockTable = malloc(sizeof(*_lockTable));
if (_lockTable != NULL) {
pthread_mutex_init(&_lockTable->lock, NULL);
memset(_lockTable->buckets, 0, sizeof(_lockTable->buckets));
}
}
static LockTable*
lock_table_lock( void )
{
pthread_once( &_lockTable_once, lock_table_init );
pthread_mutex_lock( &_lockTable->lock );
return _lockTable;
}
static void
lock_table_unlock( LockTable* t )
{
pthread_mutex_unlock( &t->lock );
}
static FileLock**
lock_table_lookup( LockTable* t, FILE* f )
{
uint32_t hash = (uint32_t)(void*)f;
FileLock** pnode;
hash = (hash >> 2) ^ (hash << 17);
pnode = &t->buckets[hash % FILE_LOCK_BUCKETS];
for (;;) {
FileLock* node = *pnode;
if (node == NULL || node->file == f)
break;
pnode = &node->next;
}
return pnode;
}
void
flockfile(FILE * fp)
{
LockTable* t = lock_table_lock();
if (t != NULL) {
FileLock** lookup = lock_table_lookup(t, fp);
FileLock* lock = *lookup;
if (lock == NULL) {
pthread_mutexattr_t attr;
/* create a new node in the hash table */
lock = malloc(sizeof(*lock));
if (lock == NULL) {
lock_table_unlock(t);
return;
}
lock->next = NULL;
lock->file = fp;
pthread_mutexattr_init(&attr);
pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
pthread_mutex_init( &lock->mutex, &attr );
*lookup = lock;
}
lock_table_unlock(t);
/* we assume that another thread didn't destroy 'lock'
* by calling fclose() on the FILE*. This can happen if
* the client is *really* buggy, but we don't care about
* such code here.
*/
pthread_mutex_lock(&lock->mutex);
}
}
int
ftrylockfile(FILE *fp)
{
int ret = -1;
LockTable* t = lock_table_lock();
if (t != NULL) {
FileLock** lookup = lock_table_lookup(t, fp);
FileLock* lock = *lookup;
lock_table_unlock(t);
/* see above comment about why we assume that 'lock' can
* be accessed from here
*/
if (lock != NULL && !pthread_mutex_trylock(&lock->mutex)) {
ret = 0; /* signal success */
}
}
return ret;
}
void
funlockfile(FILE * fp)
{
LockTable* t = lock_table_lock();
if (t != NULL) {
FileLock** lookup = lock_table_lookup(t, fp);
FileLock* lock = *lookup;
if (lock != NULL)
pthread_mutex_unlock(&lock->mutex);
lock_table_unlock(t);
}
}
/* called from fclose() to remove the file lock */
void
__fremovelock(FILE* fp)
{
LockTable* t = lock_table_lock();
if (t != NULL) {
FileLock** lookup = lock_table_lookup(t, fp);
FileLock* lock = *lookup;
if (lock != NULL) {
*lookup = lock->next;
lock->file = NULL;
}
lock_table_unlock(t);
if (lock != NULL)
free(lock);
}
}
|
