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1 | /* Read-write locks (native Windows implementation). |
2 | Copyright (C) 2005-2019 Free Software Foundation, Inc. | |
3 | ||
4 | This program is free software; you can redistribute it and/or modify | |
5 | it under the terms of the GNU General Public License as published by | |
6 | the Free Software Foundation; either version 3, or (at your option) | |
7 | any later version. | |
8 | ||
9 | This program is distributed in the hope that it will be useful, | |
10 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
12 | GNU General Public License for more details. | |
13 | ||
14 | You should have received a copy of the GNU General Public License | |
15 | along with this program; if not, see <https://www.gnu.org/licenses/>. */ | |
16 | ||
17 | /* Written by Bruno Haible <bruno@clisp.org>, 2005. | |
18 | Based on GCC's gthr-win32.h. */ | |
19 | ||
20 | #include <config.h> | |
21 | ||
22 | /* Specification. */ | |
23 | #include "windows-rwlock.h" | |
24 | ||
25 | #include <errno.h> | |
26 | #include <stdlib.h> | |
27 | ||
28 | /* In this file, the waitqueues are implemented as circular arrays. */ | |
29 | #define glwthread_waitqueue_t glwthread_carray_waitqueue_t | |
30 | ||
31 | static void | |
32 | glwthread_waitqueue_init (glwthread_waitqueue_t *wq) | |
33 | { | |
34 | wq->array = NULL; | |
35 | wq->count = 0; | |
36 | wq->alloc = 0; | |
37 | wq->offset = 0; | |
38 | } | |
39 | ||
40 | /* Enqueues the current thread, represented by an event, in a wait queue. | |
41 | Returns INVALID_HANDLE_VALUE if an allocation failure occurs. */ | |
42 | static HANDLE | |
43 | glwthread_waitqueue_add (glwthread_waitqueue_t *wq) | |
44 | { | |
45 | HANDLE event; | |
46 | unsigned int index; | |
47 | ||
48 | if (wq->count == wq->alloc) | |
49 | { | |
50 | unsigned int new_alloc = 2 * wq->alloc + 1; | |
51 | HANDLE *new_array = | |
52 | (HANDLE *) realloc (wq->array, new_alloc * sizeof (HANDLE)); | |
53 | if (new_array == NULL) | |
54 | /* No more memory. */ | |
55 | return INVALID_HANDLE_VALUE; | |
56 | /* Now is a good opportunity to rotate the array so that its contents | |
57 | starts at offset 0. */ | |
58 | if (wq->offset > 0) | |
59 | { | |
60 | unsigned int old_count = wq->count; | |
61 | unsigned int old_alloc = wq->alloc; | |
62 | unsigned int old_offset = wq->offset; | |
63 | unsigned int i; | |
64 | if (old_offset + old_count > old_alloc) | |
65 | { | |
66 | unsigned int limit = old_offset + old_count - old_alloc; | |
67 | for (i = 0; i < limit; i++) | |
68 | new_array[old_alloc + i] = new_array[i]; | |
69 | } | |
70 | for (i = 0; i < old_count; i++) | |
71 | new_array[i] = new_array[old_offset + i]; | |
72 | wq->offset = 0; | |
73 | } | |
74 | wq->array = new_array; | |
75 | wq->alloc = new_alloc; | |
76 | } | |
77 | /* Whether the created event is a manual-reset one or an auto-reset one, | |
78 | does not matter, since we will wait on it only once. */ | |
79 | event = CreateEvent (NULL, TRUE, FALSE, NULL); | |
80 | if (event == INVALID_HANDLE_VALUE) | |
81 | /* No way to allocate an event. */ | |
82 | return INVALID_HANDLE_VALUE; | |
83 | index = wq->offset + wq->count; | |
84 | if (index >= wq->alloc) | |
85 | index -= wq->alloc; | |
86 | wq->array[index] = event; | |
87 | wq->count++; | |
88 | return event; | |
89 | } | |
90 | ||
91 | /* Notifies the first thread from a wait queue and dequeues it. */ | |
92 | static void | |
93 | glwthread_waitqueue_notify_first (glwthread_waitqueue_t *wq) | |
94 | { | |
95 | SetEvent (wq->array[wq->offset + 0]); | |
96 | wq->offset++; | |
97 | wq->count--; | |
98 | if (wq->count == 0 || wq->offset == wq->alloc) | |
99 | wq->offset = 0; | |
100 | } | |
101 | ||
102 | /* Notifies all threads from a wait queue and dequeues them all. */ | |
103 | static void | |
104 | glwthread_waitqueue_notify_all (glwthread_waitqueue_t *wq) | |
105 | { | |
106 | unsigned int i; | |
107 | ||
108 | for (i = 0; i < wq->count; i++) | |
109 | { | |
110 | unsigned int index = wq->offset + i; | |
111 | if (index >= wq->alloc) | |
112 | index -= wq->alloc; | |
113 | SetEvent (wq->array[index]); | |
114 | } | |
115 | wq->count = 0; | |
116 | wq->offset = 0; | |
117 | } | |
118 | ||
119 | void | |
120 | glwthread_rwlock_init (glwthread_rwlock_t *lock) | |
121 | { | |
122 | InitializeCriticalSection (&lock->lock); | |
123 | glwthread_waitqueue_init (&lock->waiting_readers); | |
124 | glwthread_waitqueue_init (&lock->waiting_writers); | |
125 | lock->runcount = 0; | |
126 | lock->guard.done = 1; | |
127 | } | |
128 | ||
129 | int | |
130 | glwthread_rwlock_rdlock (glwthread_rwlock_t *lock) | |
131 | { | |
132 | if (!lock->guard.done) | |
133 | { | |
134 | if (InterlockedIncrement (&lock->guard.started) == 0) | |
135 | /* This thread is the first one to need this lock. Initialize it. */ | |
136 | glwthread_rwlock_init (lock); | |
137 | else | |
138 | { | |
139 | /* Don't let lock->guard.started grow and wrap around. */ | |
140 | InterlockedDecrement (&lock->guard.started); | |
141 | /* Yield the CPU while waiting for another thread to finish | |
142 | initializing this lock. */ | |
143 | while (!lock->guard.done) | |
144 | Sleep (0); | |
145 | } | |
146 | } | |
147 | EnterCriticalSection (&lock->lock); | |
148 | /* Test whether only readers are currently running, and whether the runcount | |
149 | field will not overflow, and whether no writer is waiting. The latter | |
150 | condition is because POSIX recommends that "write locks shall take | |
151 | precedence over read locks", to avoid "writer starvation". */ | |
152 | if (!(lock->runcount + 1 > 0 && lock->waiting_writers.count == 0)) | |
153 | { | |
154 | /* This thread has to wait for a while. Enqueue it among the | |
155 | waiting_readers. */ | |
156 | HANDLE event = glwthread_waitqueue_add (&lock->waiting_readers); | |
157 | if (event != INVALID_HANDLE_VALUE) | |
158 | { | |
159 | DWORD result; | |
160 | LeaveCriticalSection (&lock->lock); | |
161 | /* Wait until another thread signals this event. */ | |
162 | result = WaitForSingleObject (event, INFINITE); | |
163 | if (result == WAIT_FAILED || result == WAIT_TIMEOUT) | |
164 | abort (); | |
165 | CloseHandle (event); | |
166 | /* The thread which signalled the event already did the bookkeeping: | |
167 | removed us from the waiting_readers, incremented lock->runcount. */ | |
168 | if (!(lock->runcount > 0)) | |
169 | abort (); | |
170 | return 0; | |
171 | } | |
172 | else | |
173 | { | |
174 | /* Allocation failure. Weird. */ | |
175 | do | |
176 | { | |
177 | LeaveCriticalSection (&lock->lock); | |
178 | Sleep (1); | |
179 | EnterCriticalSection (&lock->lock); | |
180 | } | |
181 | while (!(lock->runcount + 1 > 0)); | |
182 | } | |
183 | } | |
184 | lock->runcount++; | |
185 | LeaveCriticalSection (&lock->lock); | |
186 | return 0; | |
187 | } | |
188 | ||
189 | int | |
190 | glwthread_rwlock_wrlock (glwthread_rwlock_t *lock) | |
191 | { | |
192 | if (!lock->guard.done) | |
193 | { | |
194 | if (InterlockedIncrement (&lock->guard.started) == 0) | |
195 | /* This thread is the first one to need this lock. Initialize it. */ | |
196 | glwthread_rwlock_init (lock); | |
197 | else | |
198 | { | |
199 | /* Don't let lock->guard.started grow and wrap around. */ | |
200 | InterlockedDecrement (&lock->guard.started); | |
201 | /* Yield the CPU while waiting for another thread to finish | |
202 | initializing this lock. */ | |
203 | while (!lock->guard.done) | |
204 | Sleep (0); | |
205 | } | |
206 | } | |
207 | EnterCriticalSection (&lock->lock); | |
208 | /* Test whether no readers or writers are currently running. */ | |
209 | if (!(lock->runcount == 0)) | |
210 | { | |
211 | /* This thread has to wait for a while. Enqueue it among the | |
212 | waiting_writers. */ | |
213 | HANDLE event = glwthread_waitqueue_add (&lock->waiting_writers); | |
214 | if (event != INVALID_HANDLE_VALUE) | |
215 | { | |
216 | DWORD result; | |
217 | LeaveCriticalSection (&lock->lock); | |
218 | /* Wait until another thread signals this event. */ | |
219 | result = WaitForSingleObject (event, INFINITE); | |
220 | if (result == WAIT_FAILED || result == WAIT_TIMEOUT) | |
221 | abort (); | |
222 | CloseHandle (event); | |
223 | /* The thread which signalled the event already did the bookkeeping: | |
224 | removed us from the waiting_writers, set lock->runcount = -1. */ | |
225 | if (!(lock->runcount == -1)) | |
226 | abort (); | |
227 | return 0; | |
228 | } | |
229 | else | |
230 | { | |
231 | /* Allocation failure. Weird. */ | |
232 | do | |
233 | { | |
234 | LeaveCriticalSection (&lock->lock); | |
235 | Sleep (1); | |
236 | EnterCriticalSection (&lock->lock); | |
237 | } | |
238 | while (!(lock->runcount == 0)); | |
239 | } | |
240 | } | |
241 | lock->runcount--; /* runcount becomes -1 */ | |
242 | LeaveCriticalSection (&lock->lock); | |
243 | return 0; | |
244 | } | |
245 | ||
246 | int | |
247 | glwthread_rwlock_tryrdlock (glwthread_rwlock_t *lock) | |
248 | { | |
249 | if (!lock->guard.done) | |
250 | { | |
251 | if (InterlockedIncrement (&lock->guard.started) == 0) | |
252 | /* This thread is the first one to need this lock. Initialize it. */ | |
253 | glwthread_rwlock_init (lock); | |
254 | else | |
255 | { | |
256 | /* Don't let lock->guard.started grow and wrap around. */ | |
257 | InterlockedDecrement (&lock->guard.started); | |
258 | /* Yield the CPU while waiting for another thread to finish | |
259 | initializing this lock. */ | |
260 | while (!lock->guard.done) | |
261 | Sleep (0); | |
262 | } | |
263 | } | |
264 | /* It's OK to wait for this critical section, because it is never taken for a | |
265 | long time. */ | |
266 | EnterCriticalSection (&lock->lock); | |
267 | /* Test whether only readers are currently running, and whether the runcount | |
268 | field will not overflow, and whether no writer is waiting. The latter | |
269 | condition is because POSIX recommends that "write locks shall take | |
270 | precedence over read locks", to avoid "writer starvation". */ | |
271 | if (!(lock->runcount + 1 > 0 && lock->waiting_writers.count == 0)) | |
272 | { | |
273 | /* This thread would have to wait for a while. Return instead. */ | |
274 | LeaveCriticalSection (&lock->lock); | |
275 | return EBUSY; | |
276 | } | |
277 | lock->runcount++; | |
278 | LeaveCriticalSection (&lock->lock); | |
279 | return 0; | |
280 | } | |
281 | ||
282 | int | |
283 | glwthread_rwlock_trywrlock (glwthread_rwlock_t *lock) | |
284 | { | |
285 | if (!lock->guard.done) | |
286 | { | |
287 | if (InterlockedIncrement (&lock->guard.started) == 0) | |
288 | /* This thread is the first one to need this lock. Initialize it. */ | |
289 | glwthread_rwlock_init (lock); | |
290 | else | |
291 | { | |
292 | /* Don't let lock->guard.started grow and wrap around. */ | |
293 | InterlockedDecrement (&lock->guard.started); | |
294 | /* Yield the CPU while waiting for another thread to finish | |
295 | initializing this lock. */ | |
296 | while (!lock->guard.done) | |
297 | Sleep (0); | |
298 | } | |
299 | } | |
300 | /* It's OK to wait for this critical section, because it is never taken for a | |
301 | long time. */ | |
302 | EnterCriticalSection (&lock->lock); | |
303 | /* Test whether no readers or writers are currently running. */ | |
304 | if (!(lock->runcount == 0)) | |
305 | { | |
306 | /* This thread would have to wait for a while. Return instead. */ | |
307 | LeaveCriticalSection (&lock->lock); | |
308 | return EBUSY; | |
309 | } | |
310 | lock->runcount--; /* runcount becomes -1 */ | |
311 | LeaveCriticalSection (&lock->lock); | |
312 | return 0; | |
313 | } | |
314 | ||
315 | int | |
316 | glwthread_rwlock_unlock (glwthread_rwlock_t *lock) | |
317 | { | |
318 | if (!lock->guard.done) | |
319 | return EINVAL; | |
320 | EnterCriticalSection (&lock->lock); | |
321 | if (lock->runcount < 0) | |
322 | { | |
323 | /* Drop a writer lock. */ | |
324 | if (!(lock->runcount == -1)) | |
325 | abort (); | |
326 | lock->runcount = 0; | |
327 | } | |
328 | else | |
329 | { | |
330 | /* Drop a reader lock. */ | |
331 | if (!(lock->runcount > 0)) | |
332 | { | |
333 | LeaveCriticalSection (&lock->lock); | |
334 | return EPERM; | |
335 | } | |
336 | lock->runcount--; | |
337 | } | |
338 | if (lock->runcount == 0) | |
339 | { | |
340 | /* POSIX recommends that "write locks shall take precedence over read | |
341 | locks", to avoid "writer starvation". */ | |
342 | if (lock->waiting_writers.count > 0) | |
343 | { | |
344 | /* Wake up one of the waiting writers. */ | |
345 | lock->runcount--; | |
346 | glwthread_waitqueue_notify_first (&lock->waiting_writers); | |
347 | } | |
348 | else | |
349 | { | |
350 | /* Wake up all waiting readers. */ | |
351 | lock->runcount += lock->waiting_readers.count; | |
352 | glwthread_waitqueue_notify_all (&lock->waiting_readers); | |
353 | } | |
354 | } | |
355 | LeaveCriticalSection (&lock->lock); | |
356 | return 0; | |
357 | } | |
358 | ||
359 | int | |
360 | glwthread_rwlock_destroy (glwthread_rwlock_t *lock) | |
361 | { | |
362 | if (!lock->guard.done) | |
363 | return EINVAL; | |
364 | if (lock->runcount != 0) | |
365 | return EBUSY; | |
366 | DeleteCriticalSection (&lock->lock); | |
367 | if (lock->waiting_readers.array != NULL) | |
368 | free (lock->waiting_readers.array); | |
369 | if (lock->waiting_writers.array != NULL) | |
370 | free (lock->waiting_writers.array); | |
371 | lock->guard.done = 0; | |
372 | return 0; | |
373 | } |