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1 | /* |
1 | /* |
2 | * Copyright (c) 2001-2004 Jakub Jermar |
2 | * Copyright (c) 2001-2004 Jakub Jermar |
3 | * All rights reserved. |
3 | * All rights reserved. |
4 | * |
4 | * |
5 | * Redistribution and use in source and binary forms, with or without |
5 | * Redistribution and use in source and binary forms, with or without |
6 | * modification, are permitted provided that the following conditions |
6 | * modification, are permitted provided that the following conditions |
7 | * are met: |
7 | * are met: |
8 | * |
8 | * |
9 | * - Redistributions of source code must retain the above copyright |
9 | * - Redistributions of source code must retain the above copyright |
10 | * notice, this list of conditions and the following disclaimer. |
10 | * notice, this list of conditions and the following disclaimer. |
11 | * - Redistributions in binary form must reproduce the above copyright |
11 | * - Redistributions in binary form must reproduce the above copyright |
12 | * notice, this list of conditions and the following disclaimer in the |
12 | * notice, this list of conditions and the following disclaimer in the |
13 | * documentation and/or other materials provided with the distribution. |
13 | * documentation and/or other materials provided with the distribution. |
14 | * - The name of the author may not be used to endorse or promote products |
14 | * - The name of the author may not be used to endorse or promote products |
15 | * derived from this software without specific prior written permission. |
15 | * derived from this software without specific prior written permission. |
16 | * |
16 | * |
17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
18 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
18 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
19 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
19 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
20 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
20 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
21 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
21 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
22 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
22 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
23 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
23 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
24 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
24 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
25 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
25 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
26 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
26 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
27 | */ |
27 | */ |
28 | 28 | ||
29 | /** @addtogroup sync |
29 | /** @addtogroup sync |
30 | * @{ |
30 | * @{ |
31 | */ |
31 | */ |
32 | 32 | ||
33 | /** |
33 | /** |
34 | * @file |
34 | * @file |
35 | * @brief Reader/Writer locks. |
35 | * @brief Reader/Writer locks. |
36 | * |
36 | * |
37 | * A reader/writer lock can be held by multiple readers at a time. |
37 | * A reader/writer lock can be held by multiple readers at a time. |
38 | * Or it can be exclusively held by a sole writer at a time. |
38 | * Or it can be exclusively held by a sole writer at a time. |
39 | * |
39 | * |
40 | * These locks are not recursive. |
40 | * These locks are not recursive. |
41 | * Because a technique called direct hand-off is used and because |
41 | * Because a technique called direct hand-off is used and because |
42 | * waiting takes place in a single wait queue, neither readers |
42 | * waiting takes place in a single wait queue, neither readers |
43 | * nor writers will suffer starvation. |
43 | * nor writers will suffer starvation. |
44 | * |
44 | * |
45 | * If there is a writer followed by a reader waiting for the rwlock |
45 | * If there is a writer followed by a reader waiting for the rwlock |
46 | * and the writer times out, all leading readers are automatically woken up |
46 | * and the writer times out, all leading readers are automatically woken up |
47 | * and allowed in. |
47 | * and allowed in. |
48 | */ |
48 | */ |
49 | 49 | ||
50 | /* |
50 | /* |
51 | * NOTE ON rwlock_holder_type |
51 | * NOTE ON rwlock_holder_type |
52 | * This field is set on an attempt to acquire the exclusive mutex |
52 | * This field is set on an attempt to acquire the exclusive mutex |
53 | * to the respective value depending whether the caller is a reader |
53 | * to the respective value depending whether the caller is a reader |
54 | * or a writer. The field is examined only if the thread had been |
54 | * or a writer. The field is examined only if the thread had been |
55 | * previously blocked on the exclusive mutex. Thus it is save |
55 | * previously blocked on the exclusive mutex. Thus it is save |
56 | * to store the rwlock type in the thread structure, because |
56 | * to store the rwlock type in the thread structure, because |
57 | * each thread can block on only one rwlock at a time. |
57 | * each thread can block on only one rwlock at a time. |
58 | */ |
58 | */ |
59 | 59 | ||
60 | #include <synch/rwlock.h> |
60 | #include <synch/rwlock.h> |
61 | #include <synch/spinlock.h> |
61 | #include <synch/spinlock.h> |
62 | #include <synch/mutex.h> |
62 | #include <synch/mutex.h> |
63 | #include <synch/waitq.h> |
63 | #include <synch/waitq.h> |
64 | #include <synch/synch.h> |
64 | #include <synch/synch.h> |
65 | #include <adt/list.h> |
65 | #include <adt/list.h> |
66 | #include <arch/asm.h> |
66 | #include <arch/asm.h> |
67 | #include <arch.h> |
67 | #include <arch.h> |
68 | #include <proc/thread.h> |
68 | #include <proc/thread.h> |
69 | #include <panic.h> |
69 | #include <panic.h> |
70 | 70 | ||
71 | #define ALLOW_ALL 0 |
71 | #define ALLOW_ALL 0 |
72 | #define ALLOW_READERS_ONLY 1 |
72 | #define ALLOW_READERS_ONLY 1 |
73 | 73 | ||
74 | static void let_others_in(rwlock_t *rwl, int readers_only); |
74 | static void let_others_in(rwlock_t *rwl, int readers_only); |
75 | static void release_spinlock(void *arg); |
75 | static void release_spinlock(void *arg); |
76 | 76 | ||
77 | /** Initialize reader/writer lock |
77 | /** Initialize reader/writer lock |
78 | * |
78 | * |
79 | * Initialize reader/writer lock. |
79 | * Initialize reader/writer lock. |
80 | * |
80 | * |
81 | * @param rwl Reader/Writer lock. |
81 | * @param rwl Reader/Writer lock. |
82 | */ |
82 | */ |
83 | void rwlock_initialize(rwlock_t *rwl) { |
83 | void rwlock_initialize(rwlock_t *rwl) { |
84 | spinlock_initialize(&rwl->lock, "rwlock_t"); |
84 | spinlock_initialize(&rwl->lock, "rwlock_t"); |
85 | mutex_initialize(&rwl->exclusive, MUTEX_PASSIVE); |
85 | mutex_initialize(&rwl->exclusive, MUTEX_PASSIVE); |
86 | rwl->readers_in = 0; |
86 | rwl->readers_in = 0; |
87 | } |
87 | } |
88 | 88 | ||
89 | /** Acquire reader/writer lock for reading |
89 | /** Acquire reader/writer lock for reading |
90 | * |
90 | * |
91 | * Acquire reader/writer lock for reading. |
91 | * Acquire reader/writer lock for reading. |
92 | * Timeout and willingness to block may be specified. |
92 | * Timeout and willingness to block may be specified. |
93 | * |
93 | * |
94 | * @param rwl Reader/Writer lock. |
94 | * @param rwl Reader/Writer lock. |
95 | * @param usec Timeout in microseconds. |
95 | * @param usec Timeout in microseconds. |
96 | * @param flags Specify mode of operation. |
96 | * @param flags Specify mode of operation. |
97 | * |
97 | * |
98 | * For exact description of possible combinations of |
98 | * For exact description of possible combinations of |
99 | * usec and flags, see comment for waitq_sleep_timeout(). |
99 | * usec and flags, see comment for waitq_sleep_timeout(). |
100 | * |
100 | * |
101 | * @return See comment for waitq_sleep_timeout(). |
101 | * @return See comment for waitq_sleep_timeout(). |
102 | */ |
102 | */ |
103 | int _rwlock_write_lock_timeout(rwlock_t *rwl, uint32_t usec, int flags) |
103 | int _rwlock_write_lock_timeout(rwlock_t *rwl, uint32_t usec, int flags) |
104 | { |
104 | { |
105 | ipl_t ipl; |
105 | ipl_t ipl; |
106 | int rc; |
106 | int rc; |
107 | 107 | ||
108 | ipl = interrupts_disable(); |
108 | ipl = interrupts_disable(); |
109 | spinlock_lock(&THREAD->lock); |
109 | spinlock_lock(&THREAD->lock); |
110 | THREAD->rwlock_holder_type = RWLOCK_WRITER; |
110 | THREAD->rwlock_holder_type = RWLOCK_WRITER; |
111 | spinlock_unlock(&THREAD->lock); |
111 | spinlock_unlock(&THREAD->lock); |
112 | interrupts_restore(ipl); |
112 | interrupts_restore(ipl); |
113 | 113 | ||
114 | /* |
114 | /* |
115 | * Writers take the easy part. |
115 | * Writers take the easy part. |
116 | * They just need to acquire the exclusive mutex. |
116 | * They just need to acquire the exclusive mutex. |
117 | */ |
117 | */ |
118 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, flags); |
118 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, flags); |
119 | if (SYNCH_FAILED(rc)) { |
119 | if (SYNCH_FAILED(rc)) { |
120 | 120 | ||
121 | /* |
121 | /* |
122 | * Lock operation timed out or was interrupted. |
122 | * Lock operation timed out or was interrupted. |
123 | * The state of rwl is UNKNOWN at this point. |
123 | * The state of rwl is UNKNOWN at this point. |
124 | * No claims about its holder can be made. |
124 | * No claims about its holder can be made. |
125 | */ |
125 | */ |
126 | 126 | ||
127 | ipl = interrupts_disable(); |
127 | ipl = interrupts_disable(); |
128 | spinlock_lock(&rwl->lock); |
128 | spinlock_lock(&rwl->lock); |
129 | /* |
129 | /* |
130 | * Now when rwl is locked, we can inspect it again. |
130 | * Now when rwl is locked, we can inspect it again. |
131 | * If it is held by some readers already, we can let |
131 | * If it is held by some readers already, we can let |
132 | * readers from the head of the wait queue in. |
132 | * readers from the head of the wait queue in. |
133 | */ |
133 | */ |
134 | if (rwl->readers_in) |
134 | if (rwl->readers_in) |
135 | let_others_in(rwl, ALLOW_READERS_ONLY); |
135 | let_others_in(rwl, ALLOW_READERS_ONLY); |
136 | spinlock_unlock(&rwl->lock); |
136 | spinlock_unlock(&rwl->lock); |
137 | interrupts_restore(ipl); |
137 | interrupts_restore(ipl); |
138 | } |
138 | } |
139 | 139 | ||
140 | return rc; |
140 | return rc; |
141 | } |
141 | } |
142 | 142 | ||
143 | /** Acquire reader/writer lock for writing |
143 | /** Acquire reader/writer lock for writing |
144 | * |
144 | * |
145 | * Acquire reader/writer lock for writing. |
145 | * Acquire reader/writer lock for writing. |
146 | * Timeout and willingness to block may be specified. |
146 | * Timeout and willingness to block may be specified. |
147 | * |
147 | * |
148 | * @param rwl Reader/Writer lock. |
148 | * @param rwl Reader/Writer lock. |
149 | * @param usec Timeout in microseconds. |
149 | * @param usec Timeout in microseconds. |
150 | * @param flags Select mode of operation. |
150 | * @param flags Select mode of operation. |
151 | * |
151 | * |
152 | * For exact description of possible combinations of |
152 | * For exact description of possible combinations of |
153 | * usec and flags, see comment for waitq_sleep_timeout(). |
153 | * usec and flags, see comment for waitq_sleep_timeout(). |
154 | * |
154 | * |
155 | * @return See comment for waitq_sleep_timeout(). |
155 | * @return See comment for waitq_sleep_timeout(). |
156 | */ |
156 | */ |
157 | int _rwlock_read_lock_timeout(rwlock_t *rwl, uint32_t usec, int flags) |
157 | int _rwlock_read_lock_timeout(rwlock_t *rwl, uint32_t usec, int flags) |
158 | { |
158 | { |
159 | int rc; |
159 | int rc; |
160 | ipl_t ipl; |
160 | ipl_t ipl; |
161 | 161 | ||
162 | ipl = interrupts_disable(); |
162 | ipl = interrupts_disable(); |
163 | spinlock_lock(&THREAD->lock); |
163 | spinlock_lock(&THREAD->lock); |
164 | THREAD->rwlock_holder_type = RWLOCK_READER; |
164 | THREAD->rwlock_holder_type = RWLOCK_READER; |
165 | spinlock_unlock(&THREAD->lock); |
165 | spinlock_unlock(&THREAD->lock); |
166 | 166 | ||
167 | spinlock_lock(&rwl->lock); |
167 | spinlock_lock(&rwl->lock); |
168 | 168 | ||
169 | /* |
169 | /* |
170 | * Find out whether we can get what we want without blocking. |
170 | * Find out whether we can get what we want without blocking. |
171 | */ |
171 | */ |
172 | rc = mutex_trylock(&rwl->exclusive); |
172 | rc = mutex_trylock(&rwl->exclusive); |
173 | if (SYNCH_FAILED(rc)) { |
173 | if (SYNCH_FAILED(rc)) { |
174 | 174 | ||
175 | /* |
175 | /* |
176 | * 'exclusive' mutex is being held by someone else. |
176 | * 'exclusive' mutex is being held by someone else. |
177 | * If the holder is a reader and there is no one |
177 | * If the holder is a reader and there is no one |
178 | * else waiting for it, we can enter the critical |
178 | * else waiting for it, we can enter the critical |
179 | * section. |
179 | * section. |
180 | */ |
180 | */ |
181 | 181 | ||
182 | if (rwl->readers_in) { |
182 | if (rwl->readers_in) { |
183 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
183 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
184 | if (list_empty(&rwl->exclusive.sem.wq.head)) { |
184 | if (list_empty(&rwl->exclusive.sem.wq.head)) { |
185 | /* |
185 | /* |
186 | * We can enter. |
186 | * We can enter. |
187 | */ |
187 | */ |
188 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
188 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
189 | goto shortcut; |
189 | goto shortcut; |
190 | } |
190 | } |
191 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
191 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
192 | } |
192 | } |
193 | 193 | ||
194 | /* |
194 | /* |
195 | * In order to prevent a race condition when a reader |
195 | * In order to prevent a race condition when a reader |
196 | * could block another reader at the head of the waitq, |
196 | * could block another reader at the head of the waitq, |
197 | * we register a function to unlock rwl->lock |
197 | * we register a function to unlock rwl->lock |
198 | * after this thread is put asleep. |
198 | * after this thread is put asleep. |
199 | */ |
199 | */ |
200 | #ifdef CONFIG_SMP |
200 | #ifdef CONFIG_SMP |
201 | thread_register_call_me(release_spinlock, &rwl->lock); |
201 | thread_register_call_me(release_spinlock, &rwl->lock); |
202 | #else |
202 | #else |
203 | thread_register_call_me(release_spinlock, NULL); |
203 | thread_register_call_me(release_spinlock, NULL); |
204 | #endif |
204 | #endif |
205 | 205 | ||
206 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, flags); |
206 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, flags); |
207 | switch (rc) { |
207 | switch (rc) { |
208 | case ESYNCH_WOULD_BLOCK: |
208 | case ESYNCH_WOULD_BLOCK: |
209 | /* |
209 | /* |
210 | * release_spinlock() wasn't called |
210 | * release_spinlock() wasn't called |
211 | */ |
211 | */ |
212 | thread_register_call_me(NULL, NULL); |
212 | thread_register_call_me(NULL, NULL); |
213 | spinlock_unlock(&rwl->lock); |
213 | spinlock_unlock(&rwl->lock); |
214 | case ESYNCH_TIMEOUT: |
214 | case ESYNCH_TIMEOUT: |
215 | case ESYNCH_INTERRUPTED: |
215 | case ESYNCH_INTERRUPTED: |
216 | /* |
216 | /* |
217 | * The sleep timed out. |
217 | * The sleep timed out. |
218 | * We just restore interrupt priority level. |
218 | * We just restore interrupt priority level. |
219 | */ |
219 | */ |
220 | case ESYNCH_OK_BLOCKED: |
220 | case ESYNCH_OK_BLOCKED: |
221 | /* |
221 | /* |
222 | * We were woken with rwl->readers_in already |
222 | * We were woken with rwl->readers_in already |
223 | * incremented. |
223 | * incremented. |
224 | * |
224 | * |
225 | * Note that this arrangement avoids race condition |
225 | * Note that this arrangement avoids race condition |
226 | * between two concurrent readers. (Race is avoided if |
226 | * between two concurrent readers. (Race is avoided if |
227 | * 'exclusive' is locked at the same time as |
227 | * 'exclusive' is locked at the same time as |
228 | * 'readers_in' is incremented. Same time means both |
228 | * 'readers_in' is incremented. Same time means both |
229 | * events happen atomically when rwl->lock is held.) |
229 | * events happen atomically when rwl->lock is held.) |
230 | */ |
230 | */ |
231 | interrupts_restore(ipl); |
231 | interrupts_restore(ipl); |
232 | break; |
232 | break; |
233 | case ESYNCH_OK_ATOMIC: |
233 | case ESYNCH_OK_ATOMIC: |
234 | panic("_mutex_lock_timeout() == ESYNCH_OK_ATOMIC\n"); |
234 | panic("_mutex_lock_timeout() == ESYNCH_OK_ATOMIC."); |
235 | break; |
235 | break; |
236 | default: |
236 | default: |
237 | panic("invalid ESYNCH\n"); |
237 | panic("Invalid ESYNCH."); |
238 | break; |
238 | break; |
239 | } |
239 | } |
240 | return rc; |
240 | return rc; |
241 | } |
241 | } |
242 | 242 | ||
243 | shortcut: |
243 | shortcut: |
244 | 244 | ||
245 | /* |
245 | /* |
246 | * We can increment readers_in only if we didn't go to sleep. |
246 | * We can increment readers_in only if we didn't go to sleep. |
247 | * For sleepers, rwlock_let_others_in() will do the job. |
247 | * For sleepers, rwlock_let_others_in() will do the job. |
248 | */ |
248 | */ |
249 | rwl->readers_in++; |
249 | rwl->readers_in++; |
250 | 250 | ||
251 | spinlock_unlock(&rwl->lock); |
251 | spinlock_unlock(&rwl->lock); |
252 | interrupts_restore(ipl); |
252 | interrupts_restore(ipl); |
253 | 253 | ||
254 | return ESYNCH_OK_ATOMIC; |
254 | return ESYNCH_OK_ATOMIC; |
255 | } |
255 | } |
256 | 256 | ||
257 | /** Release reader/writer lock held by writer |
257 | /** Release reader/writer lock held by writer |
258 | * |
258 | * |
259 | * Release reader/writer lock held by writer. |
259 | * Release reader/writer lock held by writer. |
260 | * Handoff reader/writer lock ownership directly |
260 | * Handoff reader/writer lock ownership directly |
261 | * to waiting readers or a writer. |
261 | * to waiting readers or a writer. |
262 | * |
262 | * |
263 | * @param rwl Reader/Writer lock. |
263 | * @param rwl Reader/Writer lock. |
264 | */ |
264 | */ |
265 | void rwlock_write_unlock(rwlock_t *rwl) |
265 | void rwlock_write_unlock(rwlock_t *rwl) |
266 | { |
266 | { |
267 | ipl_t ipl; |
267 | ipl_t ipl; |
268 | 268 | ||
269 | ipl = interrupts_disable(); |
269 | ipl = interrupts_disable(); |
270 | spinlock_lock(&rwl->lock); |
270 | spinlock_lock(&rwl->lock); |
271 | let_others_in(rwl, ALLOW_ALL); |
271 | let_others_in(rwl, ALLOW_ALL); |
272 | spinlock_unlock(&rwl->lock); |
272 | spinlock_unlock(&rwl->lock); |
273 | interrupts_restore(ipl); |
273 | interrupts_restore(ipl); |
274 | 274 | ||
275 | } |
275 | } |
276 | 276 | ||
277 | /** Release reader/writer lock held by reader |
277 | /** Release reader/writer lock held by reader |
278 | * |
278 | * |
279 | * Release reader/writer lock held by reader. |
279 | * Release reader/writer lock held by reader. |
280 | * Handoff reader/writer lock ownership directly |
280 | * Handoff reader/writer lock ownership directly |
281 | * to a waiting writer or don't do anything if more |
281 | * to a waiting writer or don't do anything if more |
282 | * readers poses the lock. |
282 | * readers poses the lock. |
283 | * |
283 | * |
284 | * @param rwl Reader/Writer lock. |
284 | * @param rwl Reader/Writer lock. |
285 | */ |
285 | */ |
286 | void rwlock_read_unlock(rwlock_t *rwl) |
286 | void rwlock_read_unlock(rwlock_t *rwl) |
287 | { |
287 | { |
288 | ipl_t ipl; |
288 | ipl_t ipl; |
289 | 289 | ||
290 | ipl = interrupts_disable(); |
290 | ipl = interrupts_disable(); |
291 | spinlock_lock(&rwl->lock); |
291 | spinlock_lock(&rwl->lock); |
292 | if (!--rwl->readers_in) |
292 | if (!--rwl->readers_in) |
293 | let_others_in(rwl, ALLOW_ALL); |
293 | let_others_in(rwl, ALLOW_ALL); |
294 | spinlock_unlock(&rwl->lock); |
294 | spinlock_unlock(&rwl->lock); |
295 | interrupts_restore(ipl); |
295 | interrupts_restore(ipl); |
296 | } |
296 | } |
297 | 297 | ||
298 | 298 | ||
299 | /** Direct handoff of reader/writer lock ownership. |
299 | /** Direct handoff of reader/writer lock ownership. |
300 | * |
300 | * |
301 | * Direct handoff of reader/writer lock ownership |
301 | * Direct handoff of reader/writer lock ownership |
302 | * to waiting readers or a writer. |
302 | * to waiting readers or a writer. |
303 | * |
303 | * |
304 | * Must be called with rwl->lock locked. |
304 | * Must be called with rwl->lock locked. |
305 | * Must be called with interrupts_disable()'d. |
305 | * Must be called with interrupts_disable()'d. |
306 | * |
306 | * |
307 | * @param rwl Reader/Writer lock. |
307 | * @param rwl Reader/Writer lock. |
308 | * @param readers_only See the description below. |
308 | * @param readers_only See the description below. |
309 | * |
309 | * |
310 | * If readers_only is false: (unlock scenario) |
310 | * If readers_only is false: (unlock scenario) |
311 | * Let the first sleeper on 'exclusive' mutex in, no matter |
311 | * Let the first sleeper on 'exclusive' mutex in, no matter |
312 | * whether it is a reader or a writer. If there are more leading |
312 | * whether it is a reader or a writer. If there are more leading |
313 | * readers in line, let each of them in. |
313 | * readers in line, let each of them in. |
314 | * |
314 | * |
315 | * Otherwise: (timeout scenario) |
315 | * Otherwise: (timeout scenario) |
316 | * Let all leading readers in. |
316 | * Let all leading readers in. |
317 | */ |
317 | */ |
318 | void let_others_in(rwlock_t *rwl, int readers_only) |
318 | void let_others_in(rwlock_t *rwl, int readers_only) |
319 | { |
319 | { |
320 | rwlock_type_t type = RWLOCK_NONE; |
320 | rwlock_type_t type = RWLOCK_NONE; |
321 | thread_t *t = NULL; |
321 | thread_t *t = NULL; |
322 | bool one_more = true; |
322 | bool one_more = true; |
323 | 323 | ||
324 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
324 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
325 | 325 | ||
326 | if (!list_empty(&rwl->exclusive.sem.wq.head)) |
326 | if (!list_empty(&rwl->exclusive.sem.wq.head)) |
327 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, |
327 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, |
328 | wq_link); |
328 | wq_link); |
329 | do { |
329 | do { |
330 | if (t) { |
330 | if (t) { |
331 | spinlock_lock(&t->lock); |
331 | spinlock_lock(&t->lock); |
332 | type = t->rwlock_holder_type; |
332 | type = t->rwlock_holder_type; |
333 | spinlock_unlock(&t->lock); |
333 | spinlock_unlock(&t->lock); |
334 | } |
334 | } |
335 | 335 | ||
336 | /* |
336 | /* |
337 | * If readers_only is true, we wake all leading readers |
337 | * If readers_only is true, we wake all leading readers |
338 | * if and only if rwl is locked by another reader. |
338 | * if and only if rwl is locked by another reader. |
339 | * Assumption: readers_only ==> rwl->readers_in |
339 | * Assumption: readers_only ==> rwl->readers_in |
340 | */ |
340 | */ |
341 | if (readers_only && (type != RWLOCK_READER)) |
341 | if (readers_only && (type != RWLOCK_READER)) |
342 | break; |
342 | break; |
343 | 343 | ||
344 | 344 | ||
345 | if (type == RWLOCK_READER) { |
345 | if (type == RWLOCK_READER) { |
346 | /* |
346 | /* |
347 | * Waking up a reader. |
347 | * Waking up a reader. |
348 | * We are responsible for incrementing rwl->readers_in |
348 | * We are responsible for incrementing rwl->readers_in |
349 | * for it. |
349 | * for it. |
350 | */ |
350 | */ |
351 | rwl->readers_in++; |
351 | rwl->readers_in++; |
352 | } |
352 | } |
353 | 353 | ||
354 | /* |
354 | /* |
355 | * Only the last iteration through this loop can increment |
355 | * Only the last iteration through this loop can increment |
356 | * rwl->exclusive.sem.wq.missed_wakeup's. All preceeding |
356 | * rwl->exclusive.sem.wq.missed_wakeup's. All preceeding |
357 | * iterations will wake up a thread. |
357 | * iterations will wake up a thread. |
358 | */ |
358 | */ |
359 | /* We call the internal version of waitq_wakeup, which |
359 | /* We call the internal version of waitq_wakeup, which |
360 | * relies on the fact that the waitq is already locked. |
360 | * relies on the fact that the waitq is already locked. |
361 | */ |
361 | */ |
362 | _waitq_wakeup_unsafe(&rwl->exclusive.sem.wq, WAKEUP_FIRST); |
362 | _waitq_wakeup_unsafe(&rwl->exclusive.sem.wq, WAKEUP_FIRST); |
363 | 363 | ||
364 | t = NULL; |
364 | t = NULL; |
365 | if (!list_empty(&rwl->exclusive.sem.wq.head)) { |
365 | if (!list_empty(&rwl->exclusive.sem.wq.head)) { |
366 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, |
366 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, |
367 | thread_t, wq_link); |
367 | thread_t, wq_link); |
368 | if (t) { |
368 | if (t) { |
369 | spinlock_lock(&t->lock); |
369 | spinlock_lock(&t->lock); |
370 | if (t->rwlock_holder_type != RWLOCK_READER) |
370 | if (t->rwlock_holder_type != RWLOCK_READER) |
371 | one_more = false; |
371 | one_more = false; |
372 | spinlock_unlock(&t->lock); |
372 | spinlock_unlock(&t->lock); |
373 | } |
373 | } |
374 | } |
374 | } |
375 | } while ((type == RWLOCK_READER) && t && one_more); |
375 | } while ((type == RWLOCK_READER) && t && one_more); |
376 | 376 | ||
377 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
377 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
378 | } |
378 | } |
379 | 379 | ||
380 | /** Release spinlock callback |
380 | /** Release spinlock callback |
381 | * |
381 | * |
382 | * This is a callback function invoked from the scheduler. |
382 | * This is a callback function invoked from the scheduler. |
383 | * The callback is registered in _rwlock_read_lock_timeout(). |
383 | * The callback is registered in _rwlock_read_lock_timeout(). |
384 | * |
384 | * |
385 | * @param arg Spinlock. |
385 | * @param arg Spinlock. |
386 | */ |
386 | */ |
387 | void release_spinlock(void *arg) |
387 | void release_spinlock(void *arg) |
388 | { |
388 | { |
389 | spinlock_unlock((spinlock_t *) arg); |
389 | spinlock_unlock((spinlock_t *) arg); |
390 | } |
390 | } |
391 | 391 | ||
392 | /** @} |
392 | /** @} |
393 | */ |
393 | */ |
394 | 394 |