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c0c3707f | 1 | /* Read-write locks (native Windows implementation). |
9c9d63b1 | 2 | Copyright (C) 2005-2021 Free Software Foundation, Inc. |
c0c3707f CB |
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 | ||
698be2d8 CB |
28 | /* Don't assume that UNICODE is not defined. */ |
29 | #undef CreateEvent | |
30 | #define CreateEvent CreateEventA | |
31 | ||
c0c3707f CB |
32 | /* In this file, the waitqueues are implemented as circular arrays. */ |
33 | #define glwthread_waitqueue_t glwthread_carray_waitqueue_t | |
34 | ||
35 | static void | |
36 | glwthread_waitqueue_init (glwthread_waitqueue_t *wq) | |
37 | { | |
38 | wq->array = NULL; | |
39 | wq->count = 0; | |
40 | wq->alloc = 0; | |
41 | wq->offset = 0; | |
42 | } | |
43 | ||
44 | /* Enqueues the current thread, represented by an event, in a wait queue. | |
45 | Returns INVALID_HANDLE_VALUE if an allocation failure occurs. */ | |
46 | static HANDLE | |
47 | glwthread_waitqueue_add (glwthread_waitqueue_t *wq) | |
48 | { | |
49 | HANDLE event; | |
50 | unsigned int index; | |
51 | ||
52 | if (wq->count == wq->alloc) | |
53 | { | |
54 | unsigned int new_alloc = 2 * wq->alloc + 1; | |
55 | HANDLE *new_array = | |
56 | (HANDLE *) realloc (wq->array, new_alloc * sizeof (HANDLE)); | |
57 | if (new_array == NULL) | |
58 | /* No more memory. */ | |
59 | return INVALID_HANDLE_VALUE; | |
60 | /* Now is a good opportunity to rotate the array so that its contents | |
61 | starts at offset 0. */ | |
62 | if (wq->offset > 0) | |
63 | { | |
64 | unsigned int old_count = wq->count; | |
65 | unsigned int old_alloc = wq->alloc; | |
66 | unsigned int old_offset = wq->offset; | |
67 | unsigned int i; | |
68 | if (old_offset + old_count > old_alloc) | |
69 | { | |
70 | unsigned int limit = old_offset + old_count - old_alloc; | |
71 | for (i = 0; i < limit; i++) | |
72 | new_array[old_alloc + i] = new_array[i]; | |
73 | } | |
74 | for (i = 0; i < old_count; i++) | |
75 | new_array[i] = new_array[old_offset + i]; | |
76 | wq->offset = 0; | |
77 | } | |
78 | wq->array = new_array; | |
79 | wq->alloc = new_alloc; | |
80 | } | |
81 | /* Whether the created event is a manual-reset one or an auto-reset one, | |
82 | does not matter, since we will wait on it only once. */ | |
83 | event = CreateEvent (NULL, TRUE, FALSE, NULL); | |
84 | if (event == INVALID_HANDLE_VALUE) | |
85 | /* No way to allocate an event. */ | |
86 | return INVALID_HANDLE_VALUE; | |
87 | index = wq->offset + wq->count; | |
88 | if (index >= wq->alloc) | |
89 | index -= wq->alloc; | |
90 | wq->array[index] = event; | |
91 | wq->count++; | |
92 | return event; | |
93 | } | |
94 | ||
95 | /* Notifies the first thread from a wait queue and dequeues it. */ | |
96 | static void | |
97 | glwthread_waitqueue_notify_first (glwthread_waitqueue_t *wq) | |
98 | { | |
99 | SetEvent (wq->array[wq->offset + 0]); | |
100 | wq->offset++; | |
101 | wq->count--; | |
102 | if (wq->count == 0 || wq->offset == wq->alloc) | |
103 | wq->offset = 0; | |
104 | } | |
105 | ||
106 | /* Notifies all threads from a wait queue and dequeues them all. */ | |
107 | static void | |
108 | glwthread_waitqueue_notify_all (glwthread_waitqueue_t *wq) | |
109 | { | |
110 | unsigned int i; | |
111 | ||
112 | for (i = 0; i < wq->count; i++) | |
113 | { | |
114 | unsigned int index = wq->offset + i; | |
115 | if (index >= wq->alloc) | |
116 | index -= wq->alloc; | |
117 | SetEvent (wq->array[index]); | |
118 | } | |
119 | wq->count = 0; | |
120 | wq->offset = 0; | |
121 | } | |
122 | ||
123 | void | |
124 | glwthread_rwlock_init (glwthread_rwlock_t *lock) | |
125 | { | |
126 | InitializeCriticalSection (&lock->lock); | |
127 | glwthread_waitqueue_init (&lock->waiting_readers); | |
128 | glwthread_waitqueue_init (&lock->waiting_writers); | |
129 | lock->runcount = 0; | |
130 | lock->guard.done = 1; | |
131 | } | |
132 | ||
133 | int | |
134 | glwthread_rwlock_rdlock (glwthread_rwlock_t *lock) | |
135 | { | |
136 | if (!lock->guard.done) | |
137 | { | |
138 | if (InterlockedIncrement (&lock->guard.started) == 0) | |
139 | /* This thread is the first one to need this lock. Initialize it. */ | |
140 | glwthread_rwlock_init (lock); | |
141 | else | |
142 | { | |
143 | /* Don't let lock->guard.started grow and wrap around. */ | |
144 | InterlockedDecrement (&lock->guard.started); | |
145 | /* Yield the CPU while waiting for another thread to finish | |
146 | initializing this lock. */ | |
147 | while (!lock->guard.done) | |
148 | Sleep (0); | |
149 | } | |
150 | } | |
151 | EnterCriticalSection (&lock->lock); | |
152 | /* Test whether only readers are currently running, and whether the runcount | |
153 | field will not overflow, and whether no writer is waiting. The latter | |
154 | condition is because POSIX recommends that "write locks shall take | |
155 | precedence over read locks", to avoid "writer starvation". */ | |
156 | if (!(lock->runcount + 1 > 0 && lock->waiting_writers.count == 0)) | |
157 | { | |
158 | /* This thread has to wait for a while. Enqueue it among the | |
159 | waiting_readers. */ | |
160 | HANDLE event = glwthread_waitqueue_add (&lock->waiting_readers); | |
161 | if (event != INVALID_HANDLE_VALUE) | |
162 | { | |
163 | DWORD result; | |
164 | LeaveCriticalSection (&lock->lock); | |
165 | /* Wait until another thread signals this event. */ | |
166 | result = WaitForSingleObject (event, INFINITE); | |
167 | if (result == WAIT_FAILED || result == WAIT_TIMEOUT) | |
168 | abort (); | |
169 | CloseHandle (event); | |
170 | /* The thread which signalled the event already did the bookkeeping: | |
171 | removed us from the waiting_readers, incremented lock->runcount. */ | |
172 | if (!(lock->runcount > 0)) | |
173 | abort (); | |
174 | return 0; | |
175 | } | |
176 | else | |
177 | { | |
178 | /* Allocation failure. Weird. */ | |
179 | do | |
180 | { | |
181 | LeaveCriticalSection (&lock->lock); | |
182 | Sleep (1); | |
183 | EnterCriticalSection (&lock->lock); | |
184 | } | |
185 | while (!(lock->runcount + 1 > 0)); | |
186 | } | |
187 | } | |
188 | lock->runcount++; | |
189 | LeaveCriticalSection (&lock->lock); | |
190 | return 0; | |
191 | } | |
192 | ||
193 | int | |
194 | glwthread_rwlock_wrlock (glwthread_rwlock_t *lock) | |
195 | { | |
196 | if (!lock->guard.done) | |
197 | { | |
198 | if (InterlockedIncrement (&lock->guard.started) == 0) | |
199 | /* This thread is the first one to need this lock. Initialize it. */ | |
200 | glwthread_rwlock_init (lock); | |
201 | else | |
202 | { | |
203 | /* Don't let lock->guard.started grow and wrap around. */ | |
204 | InterlockedDecrement (&lock->guard.started); | |
205 | /* Yield the CPU while waiting for another thread to finish | |
206 | initializing this lock. */ | |
207 | while (!lock->guard.done) | |
208 | Sleep (0); | |
209 | } | |
210 | } | |
211 | EnterCriticalSection (&lock->lock); | |
212 | /* Test whether no readers or writers are currently running. */ | |
213 | if (!(lock->runcount == 0)) | |
214 | { | |
215 | /* This thread has to wait for a while. Enqueue it among the | |
216 | waiting_writers. */ | |
217 | HANDLE event = glwthread_waitqueue_add (&lock->waiting_writers); | |
218 | if (event != INVALID_HANDLE_VALUE) | |
219 | { | |
220 | DWORD result; | |
221 | LeaveCriticalSection (&lock->lock); | |
222 | /* Wait until another thread signals this event. */ | |
223 | result = WaitForSingleObject (event, INFINITE); | |
224 | if (result == WAIT_FAILED || result == WAIT_TIMEOUT) | |
225 | abort (); | |
226 | CloseHandle (event); | |
227 | /* The thread which signalled the event already did the bookkeeping: | |
228 | removed us from the waiting_writers, set lock->runcount = -1. */ | |
229 | if (!(lock->runcount == -1)) | |
230 | abort (); | |
231 | return 0; | |
232 | } | |
233 | else | |
234 | { | |
235 | /* Allocation failure. Weird. */ | |
236 | do | |
237 | { | |
238 | LeaveCriticalSection (&lock->lock); | |
239 | Sleep (1); | |
240 | EnterCriticalSection (&lock->lock); | |
241 | } | |
242 | while (!(lock->runcount == 0)); | |
243 | } | |
244 | } | |
245 | lock->runcount--; /* runcount becomes -1 */ | |
246 | LeaveCriticalSection (&lock->lock); | |
247 | return 0; | |
248 | } | |
249 | ||
250 | int | |
251 | glwthread_rwlock_tryrdlock (glwthread_rwlock_t *lock) | |
252 | { | |
253 | if (!lock->guard.done) | |
254 | { | |
255 | if (InterlockedIncrement (&lock->guard.started) == 0) | |
256 | /* This thread is the first one to need this lock. Initialize it. */ | |
257 | glwthread_rwlock_init (lock); | |
258 | else | |
259 | { | |
260 | /* Don't let lock->guard.started grow and wrap around. */ | |
261 | InterlockedDecrement (&lock->guard.started); | |
262 | /* Yield the CPU while waiting for another thread to finish | |
263 | initializing this lock. */ | |
264 | while (!lock->guard.done) | |
265 | Sleep (0); | |
266 | } | |
267 | } | |
268 | /* It's OK to wait for this critical section, because it is never taken for a | |
269 | long time. */ | |
270 | EnterCriticalSection (&lock->lock); | |
271 | /* Test whether only readers are currently running, and whether the runcount | |
272 | field will not overflow, and whether no writer is waiting. The latter | |
273 | condition is because POSIX recommends that "write locks shall take | |
274 | precedence over read locks", to avoid "writer starvation". */ | |
275 | if (!(lock->runcount + 1 > 0 && lock->waiting_writers.count == 0)) | |
276 | { | |
277 | /* This thread would have to wait for a while. Return instead. */ | |
278 | LeaveCriticalSection (&lock->lock); | |
279 | return EBUSY; | |
280 | } | |
281 | lock->runcount++; | |
282 | LeaveCriticalSection (&lock->lock); | |
283 | return 0; | |
284 | } | |
285 | ||
286 | int | |
287 | glwthread_rwlock_trywrlock (glwthread_rwlock_t *lock) | |
288 | { | |
289 | if (!lock->guard.done) | |
290 | { | |
291 | if (InterlockedIncrement (&lock->guard.started) == 0) | |
292 | /* This thread is the first one to need this lock. Initialize it. */ | |
293 | glwthread_rwlock_init (lock); | |
294 | else | |
295 | { | |
296 | /* Don't let lock->guard.started grow and wrap around. */ | |
297 | InterlockedDecrement (&lock->guard.started); | |
298 | /* Yield the CPU while waiting for another thread to finish | |
299 | initializing this lock. */ | |
300 | while (!lock->guard.done) | |
301 | Sleep (0); | |
302 | } | |
303 | } | |
304 | /* It's OK to wait for this critical section, because it is never taken for a | |
305 | long time. */ | |
306 | EnterCriticalSection (&lock->lock); | |
307 | /* Test whether no readers or writers are currently running. */ | |
308 | if (!(lock->runcount == 0)) | |
309 | { | |
310 | /* This thread would have to wait for a while. Return instead. */ | |
311 | LeaveCriticalSection (&lock->lock); | |
312 | return EBUSY; | |
313 | } | |
314 | lock->runcount--; /* runcount becomes -1 */ | |
315 | LeaveCriticalSection (&lock->lock); | |
316 | return 0; | |
317 | } | |
318 | ||
319 | int | |
320 | glwthread_rwlock_unlock (glwthread_rwlock_t *lock) | |
321 | { | |
322 | if (!lock->guard.done) | |
323 | return EINVAL; | |
324 | EnterCriticalSection (&lock->lock); | |
325 | if (lock->runcount < 0) | |
326 | { | |
327 | /* Drop a writer lock. */ | |
328 | if (!(lock->runcount == -1)) | |
329 | abort (); | |
330 | lock->runcount = 0; | |
331 | } | |
332 | else | |
333 | { | |
334 | /* Drop a reader lock. */ | |
335 | if (!(lock->runcount > 0)) | |
336 | { | |
337 | LeaveCriticalSection (&lock->lock); | |
338 | return EPERM; | |
339 | } | |
340 | lock->runcount--; | |
341 | } | |
342 | if (lock->runcount == 0) | |
343 | { | |
344 | /* POSIX recommends that "write locks shall take precedence over read | |
345 | locks", to avoid "writer starvation". */ | |
346 | if (lock->waiting_writers.count > 0) | |
347 | { | |
348 | /* Wake up one of the waiting writers. */ | |
349 | lock->runcount--; | |
350 | glwthread_waitqueue_notify_first (&lock->waiting_writers); | |
351 | } | |
352 | else | |
353 | { | |
354 | /* Wake up all waiting readers. */ | |
355 | lock->runcount += lock->waiting_readers.count; | |
356 | glwthread_waitqueue_notify_all (&lock->waiting_readers); | |
357 | } | |
358 | } | |
359 | LeaveCriticalSection (&lock->lock); | |
360 | return 0; | |
361 | } | |
362 | ||
363 | int | |
364 | glwthread_rwlock_destroy (glwthread_rwlock_t *lock) | |
365 | { | |
366 | if (!lock->guard.done) | |
367 | return EINVAL; | |
368 | if (lock->runcount != 0) | |
369 | return EBUSY; | |
370 | DeleteCriticalSection (&lock->lock); | |
371 | if (lock->waiting_readers.array != NULL) | |
372 | free (lock->waiting_readers.array); | |
373 | if (lock->waiting_writers.array != NULL) | |
374 | free (lock->waiting_writers.array); | |
375 | lock->guard.done = 0; | |
376 | return 0; | |
377 | } |