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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 | 29 | ||
30 | /* |
30 | /* |
31 | * Reader/Writer locks |
31 | * Reader/Writer locks |
32 | */ |
32 | */ |
33 | 33 | ||
34 | /* |
34 | /* |
35 | * These locks are not recursive. |
35 | * These locks are not recursive. |
36 | * Neither readers nor writers will suffer starvation. |
36 | * Neither readers nor writers will suffer starvation. |
37 | * |
37 | * |
38 | * If there is a writer followed by a reader waiting for the rwlock |
38 | * If there is a writer followed by a reader waiting for the rwlock |
39 | * and the writer times out, all leading readers are automatically woken up |
39 | * and the writer times out, all leading readers are automatically woken up |
40 | * and allowed in. |
40 | * and allowed in. |
41 | */ |
41 | */ |
42 | 42 | ||
43 | /* |
43 | /* |
44 | * NOTE ON rwlock_holder_type |
44 | * NOTE ON rwlock_holder_type |
45 | * This field is set on an attempt to acquire the exclusive mutex |
45 | * This field is set on an attempt to acquire the exclusive mutex |
46 | * to the respective value depending whether the caller is a reader |
46 | * to the respective value depending whether the caller is a reader |
47 | * or a writer. The field is examined only if the thread had been |
47 | * or a writer. The field is examined only if the thread had been |
48 | * previously blocked on the exclusive mutex. Thus it is save |
48 | * previously blocked on the exclusive mutex. Thus it is save |
49 | * to store the rwlock type in the thread structure, because |
49 | * to store the rwlock type in the thread structure, because |
50 | * each thread can block on only one rwlock at a time. |
50 | * each thread can block on only one rwlock at a time. |
51 | */ |
51 | */ |
52 | 52 | ||
53 | #include <synch/rwlock.h> |
53 | #include <synch/rwlock.h> |
54 | #include <synch/spinlock.h> |
54 | #include <synch/spinlock.h> |
55 | #include <synch/mutex.h> |
55 | #include <synch/mutex.h> |
56 | #include <synch/waitq.h> |
56 | #include <synch/waitq.h> |
57 | #include <synch/synch.h> |
57 | #include <synch/synch.h> |
58 | #include <list.h> |
58 | #include <list.h> |
59 | #include <typedefs.h> |
59 | #include <typedefs.h> |
60 | #include <arch/asm.h> |
60 | #include <arch/asm.h> |
61 | #include <arch.h> |
61 | #include <arch.h> |
62 | #include <proc/thread.h> |
62 | #include <proc/thread.h> |
63 | #include <panic.h> |
63 | #include <panic.h> |
64 | 64 | ||
65 | #define ALLOW_ALL 0 |
65 | #define ALLOW_ALL 0 |
66 | #define ALLOW_READERS_ONLY 1 |
66 | #define ALLOW_READERS_ONLY 1 |
67 | 67 | ||
68 | static void let_others_in(rwlock_t *rwl, int readers_only); |
68 | static void let_others_in(rwlock_t *rwl, int readers_only); |
69 | static void release_spinlock(void *arg); |
69 | static void release_spinlock(void *arg); |
70 | 70 | ||
71 | /** Initialize reader/writer lock |
71 | /** Initialize reader/writer lock |
72 | * |
72 | * |
73 | * Initialize reader/writer lock. |
73 | * Initialize reader/writer lock. |
74 | * |
74 | * |
75 | * @param rwl Reader/Writer lock. |
75 | * @param rwl Reader/Writer lock. |
76 | */ |
76 | */ |
77 | void rwlock_initialize(rwlock_t *rwl) { |
77 | void rwlock_initialize(rwlock_t *rwl) { |
78 | spinlock_initialize(&rwl->lock); |
78 | spinlock_initialize(&rwl->lock); |
79 | mutex_initialize(&rwl->exclusive); |
79 | mutex_initialize(&rwl->exclusive); |
80 | rwl->readers_in = 0; |
80 | rwl->readers_in = 0; |
81 | } |
81 | } |
82 | 82 | ||
83 | /** Acquire reader/writer lock for reading |
83 | /** Acquire reader/writer lock for reading |
84 | * |
84 | * |
85 | * Acquire reader/writer lock for reading. |
85 | * Acquire reader/writer lock for reading. |
86 | * Timeout and willingness to block may be specified. |
86 | * Timeout and willingness to block may be specified. |
87 | * |
87 | * |
88 | * @param rwl Reader/Writer lock. |
88 | * @param rwl Reader/Writer lock. |
89 | * @param usec Timeout in microseconds. |
89 | * @param usec Timeout in microseconds. |
90 | * @param trylock Switches between blocking and non-blocking mode. |
90 | * @param trylock Switches between blocking and non-blocking mode. |
91 | * |
91 | * |
92 | * For exact description of possible combinations of |
92 | * For exact description of possible combinations of |
93 | * 'usec' and 'trylock', see comment for waitq_sleep_timeout(). |
93 | * 'usec' and 'trylock', see comment for waitq_sleep_timeout(). |
94 | * |
94 | * |
95 | * @return See comment for waitq_sleep_timeout(). |
95 | * @return See comment for waitq_sleep_timeout(). |
96 | */ |
96 | */ |
97 | int _rwlock_write_lock_timeout(rwlock_t *rwl, __u32 usec, int trylock) |
97 | int _rwlock_write_lock_timeout(rwlock_t *rwl, __u32 usec, int trylock) |
98 | { |
98 | { |
99 | ipl_t ipl; |
99 | ipl_t ipl; |
100 | int rc; |
100 | int rc; |
101 | 101 | ||
102 | ipl = interrupts_disable(); |
102 | ipl = interrupts_disable(); |
103 | spinlock_lock(&THREAD->lock); |
103 | spinlock_lock(&THREAD->lock); |
104 | THREAD->rwlock_holder_type = RWLOCK_WRITER; |
104 | THREAD->rwlock_holder_type = RWLOCK_WRITER; |
105 | spinlock_unlock(&THREAD->lock); |
105 | spinlock_unlock(&THREAD->lock); |
106 | interrupts_restore(ipl); |
106 | interrupts_restore(ipl); |
107 | 107 | ||
108 | /* |
108 | /* |
109 | * Writers take the easy part. |
109 | * Writers take the easy part. |
110 | * They just need to acquire the exclusive mutex. |
110 | * They just need to acquire the exclusive mutex. |
111 | */ |
111 | */ |
112 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, trylock); |
112 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, trylock); |
113 | if (SYNCH_FAILED(rc)) { |
113 | if (SYNCH_FAILED(rc)) { |
114 | 114 | ||
115 | /* |
115 | /* |
116 | * Lock operation timed out. |
116 | * Lock operation timed out. |
117 | * The state of rwl is UNKNOWN at this point. |
117 | * The state of rwl is UNKNOWN at this point. |
118 | * No claims about its holder can be made. |
118 | * No claims about its holder can be made. |
119 | */ |
119 | */ |
120 | 120 | ||
121 | ipl = interrupts_disable(); |
121 | ipl = interrupts_disable(); |
122 | spinlock_lock(&rwl->lock); |
122 | spinlock_lock(&rwl->lock); |
123 | /* |
123 | /* |
124 | * Now when rwl is locked, we can inspect it again. |
124 | * Now when rwl is locked, we can inspect it again. |
125 | * If it is held by some readers already, we can let |
125 | * If it is held by some readers already, we can let |
126 | * readers from the head of the wait queue in. |
126 | * readers from the head of the wait queue in. |
127 | */ |
127 | */ |
128 | if (rwl->readers_in) |
128 | if (rwl->readers_in) |
129 | let_others_in(rwl, ALLOW_READERS_ONLY); |
129 | let_others_in(rwl, ALLOW_READERS_ONLY); |
130 | spinlock_unlock(&rwl->lock); |
130 | spinlock_unlock(&rwl->lock); |
131 | interrupts_restore(ipl); |
131 | interrupts_restore(ipl); |
132 | } |
132 | } |
133 | 133 | ||
134 | return rc; |
134 | return rc; |
135 | } |
135 | } |
136 | 136 | ||
137 | /** Acquire reader/writer lock for writing |
137 | /** Acquire reader/writer lock for writing |
138 | * |
138 | * |
139 | * Acquire reader/writer lock for writing. |
139 | * Acquire reader/writer lock for writing. |
140 | * Timeout and willingness to block may be specified. |
140 | * Timeout and willingness to block may be specified. |
141 | * |
141 | * |
142 | * @param rwl Reader/Writer lock. |
142 | * @param rwl Reader/Writer lock. |
143 | * @param usec Timeout in microseconds. |
143 | * @param usec Timeout in microseconds. |
144 | * @param trylock Switches between blocking and non-blocking mode. |
144 | * @param trylock Switches between blocking and non-blocking mode. |
145 | * |
145 | * |
146 | * For exact description of possible combinations of |
146 | * For exact description of possible combinations of |
147 | * 'usec' and 'trylock', see comment for waitq_sleep_timeout(). |
147 | * 'usec' and 'trylock', see comment for waitq_sleep_timeout(). |
148 | * |
148 | * |
149 | * @return See comment for waitq_sleep_timeout(). |
149 | * @return See comment for waitq_sleep_timeout(). |
150 | */ |
150 | */ |
151 | int _rwlock_read_lock_timeout(rwlock_t *rwl, __u32 usec, int trylock) |
151 | int _rwlock_read_lock_timeout(rwlock_t *rwl, __u32 usec, int trylock) |
152 | { |
152 | { |
153 | int rc; |
153 | int rc; |
154 | ipl_t ipl; |
154 | ipl_t ipl; |
155 | 155 | ||
156 | ipl = interrupts_disable(); |
156 | ipl = interrupts_disable(); |
157 | spinlock_lock(&THREAD->lock); |
157 | spinlock_lock(&THREAD->lock); |
158 | THREAD->rwlock_holder_type = RWLOCK_READER; |
158 | THREAD->rwlock_holder_type = RWLOCK_READER; |
159 | spinlock_unlock(&THREAD->lock); |
159 | spinlock_unlock(&THREAD->lock); |
160 | 160 | ||
161 | spinlock_lock(&rwl->lock); |
161 | spinlock_lock(&rwl->lock); |
162 | 162 | ||
163 | /* |
163 | /* |
164 | * Find out whether we can get what we want without blocking. |
164 | * Find out whether we can get what we want without blocking. |
165 | */ |
165 | */ |
166 | rc = mutex_trylock(&rwl->exclusive); |
166 | rc = mutex_trylock(&rwl->exclusive); |
167 | if (SYNCH_FAILED(rc)) { |
167 | if (SYNCH_FAILED(rc)) { |
168 | 168 | ||
169 | /* |
169 | /* |
170 | * 'exclusive' mutex is being held by someone else. |
170 | * 'exclusive' mutex is being held by someone else. |
171 | * If the holder is a reader and there is no one |
171 | * If the holder is a reader and there is no one |
172 | * else waiting for it, we can enter the critical |
172 | * else waiting for it, we can enter the critical |
173 | * section. |
173 | * section. |
174 | */ |
174 | */ |
175 | 175 | ||
176 | if (rwl->readers_in) { |
176 | if (rwl->readers_in) { |
177 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
177 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
178 | if (list_empty(&rwl->exclusive.sem.wq.head)) { |
178 | if (list_empty(&rwl->exclusive.sem.wq.head)) { |
179 | /* |
179 | /* |
180 | * We can enter. |
180 | * We can enter. |
181 | */ |
181 | */ |
182 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
182 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
183 | goto shortcut; |
183 | goto shortcut; |
184 | } |
184 | } |
185 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
185 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
186 | } |
186 | } |
187 | 187 | ||
188 | /* |
188 | /* |
189 | * In order to prevent a race condition when a reader |
189 | * In order to prevent a race condition when a reader |
190 | * could block another reader at the head of the waitq, |
190 | * could block another reader at the head of the waitq, |
191 | * we register a function to unlock rwl->lock |
191 | * we register a function to unlock rwl->lock |
192 | * after this thread is put asleep. |
192 | * after this thread is put asleep. |
193 | */ |
193 | */ |
194 | thread_register_call_me(release_spinlock, &rwl->lock); |
194 | thread_register_call_me(release_spinlock, &rwl->lock); |
195 | 195 | ||
196 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, trylock); |
196 | rc = _mutex_lock_timeout(&rwl->exclusive, usec, trylock); |
197 | switch (rc) { |
197 | switch (rc) { |
198 | case ESYNCH_WOULD_BLOCK: |
198 | case ESYNCH_WOULD_BLOCK: |
199 | /* |
199 | /* |
200 | * release_spinlock() wasn't called |
200 | * release_spinlock() wasn't called |
201 | */ |
201 | */ |
202 | thread_register_call_me(NULL, NULL); |
202 | thread_register_call_me(NULL, NULL); |
203 | spinlock_unlock(&rwl->lock); |
203 | spinlock_unlock(&rwl->lock); |
204 | case ESYNCH_TIMEOUT: |
204 | case ESYNCH_TIMEOUT: |
205 | /* |
205 | /* |
206 | * The sleep timeouted. |
206 | * The sleep timeouted. |
207 | * We just restore interrupt priority level. |
207 | * We just restore interrupt priority level. |
208 | */ |
208 | */ |
209 | case ESYNCH_OK_BLOCKED: |
209 | case ESYNCH_OK_BLOCKED: |
210 | /* |
210 | /* |
211 | * We were woken with rwl->readers_in already incremented. |
211 | * We were woken with rwl->readers_in already incremented. |
212 | * Note that this arrangement avoids race condition between |
212 | * Note that this arrangement avoids race condition between |
213 | * two concurrent readers. (Race is avoided if 'exclusive' is |
213 | * two concurrent readers. (Race is avoided if 'exclusive' is |
214 | * locked at the same time as 'readers_in' is incremented. |
214 | * locked at the same time as 'readers_in' is incremented. |
215 | * Same time means both events happen atomically when |
215 | * Same time means both events happen atomically when |
216 | * rwl->lock is held.) |
216 | * rwl->lock is held.) |
217 | */ |
217 | */ |
218 | interrupts_restore(ipl); |
218 | interrupts_restore(ipl); |
219 | break; |
219 | break; |
220 | case ESYNCH_OK_ATOMIC: |
220 | case ESYNCH_OK_ATOMIC: |
221 | panic("_mutex_lock_timeout()==ESYNCH_OK_ATOMIC"); |
221 | panic("_mutex_lock_timeout()==ESYNCH_OK_ATOMIC"); |
222 | break; |
222 | break; |
223 | dafault: |
223 | dafault: |
224 | panic("invalid ESYNCH"); |
224 | panic("invalid ESYNCH"); |
225 | break; |
225 | break; |
226 | } |
226 | } |
227 | return rc; |
227 | return rc; |
228 | } |
228 | } |
229 | 229 | ||
230 | shortcut: |
230 | shortcut: |
231 | 231 | ||
232 | /* |
232 | /* |
233 | * We can increment readers_in only if we didn't go to sleep. |
233 | * We can increment readers_in only if we didn't go to sleep. |
234 | * For sleepers, rwlock_let_others_in() will do the job. |
234 | * For sleepers, rwlock_let_others_in() will do the job. |
235 | */ |
235 | */ |
236 | rwl->readers_in++; |
236 | rwl->readers_in++; |
237 | 237 | ||
238 | spinlock_unlock(&rwl->lock); |
238 | spinlock_unlock(&rwl->lock); |
239 | interrupts_restore(ipl); |
239 | interrupts_restore(ipl); |
240 | 240 | ||
241 | return ESYNCH_OK_ATOMIC; |
241 | return ESYNCH_OK_ATOMIC; |
242 | } |
242 | } |
243 | 243 | ||
244 | /** Release reader/writer lock held by writer |
244 | /** Release reader/writer lock held by writer |
245 | * |
245 | * |
246 | * Release reader/writer lock held by writer. |
246 | * Release reader/writer lock held by writer. |
247 | * Handoff reader/writer lock ownership directly |
247 | * Handoff reader/writer lock ownership directly |
248 | * to waiting readers or a writer. |
248 | * to waiting readers or a writer. |
249 | * |
249 | * |
250 | * @param rwl Reader/Writer lock. |
250 | * @param rwl Reader/Writer lock. |
251 | */ |
251 | */ |
252 | void rwlock_write_unlock(rwlock_t *rwl) |
252 | void rwlock_write_unlock(rwlock_t *rwl) |
253 | { |
253 | { |
254 | ipl_t ipl; |
254 | ipl_t ipl; |
255 | 255 | ||
256 | ipl = interrupts_disable(); |
256 | ipl = interrupts_disable(); |
257 | spinlock_lock(&rwl->lock); |
257 | spinlock_lock(&rwl->lock); |
258 | let_others_in(rwl, ALLOW_ALL); |
258 | let_others_in(rwl, ALLOW_ALL); |
259 | spinlock_unlock(&rwl->lock); |
259 | spinlock_unlock(&rwl->lock); |
260 | interrupts_restore(ipl); |
260 | interrupts_restore(ipl); |
261 | 261 | ||
262 | } |
262 | } |
263 | 263 | ||
264 | /** Release reader/writer lock held by reader |
264 | /** Release reader/writer lock held by reader |
265 | * |
265 | * |
266 | * Release reader/writer lock held by reader. |
266 | * Release reader/writer lock held by reader. |
267 | * Handoff reader/writer lock ownership directly |
267 | * Handoff reader/writer lock ownership directly |
268 | * to a waiting writer or don't do anything if more |
268 | * to a waiting writer or don't do anything if more |
269 | * readers poses the lock. |
269 | * readers poses the lock. |
270 | * |
270 | * |
271 | * @param rwl Reader/Writer lock. |
271 | * @param rwl Reader/Writer lock. |
272 | */ |
272 | */ |
273 | void rwlock_read_unlock(rwlock_t *rwl) |
273 | void rwlock_read_unlock(rwlock_t *rwl) |
274 | { |
274 | { |
275 | ipl_t ipl; |
275 | ipl_t ipl; |
276 | 276 | ||
277 | ipl = interrupts_disable(); |
277 | ipl = interrupts_disable(); |
278 | spinlock_lock(&rwl->lock); |
278 | spinlock_lock(&rwl->lock); |
279 | if (!--rwl->readers_in) |
279 | if (!--rwl->readers_in) |
280 | let_others_in(rwl, ALLOW_ALL); |
280 | let_others_in(rwl, ALLOW_ALL); |
281 | spinlock_unlock(&rwl->lock); |
281 | spinlock_unlock(&rwl->lock); |
282 | interrupts_restore(ipl); |
282 | interrupts_restore(ipl); |
283 | } |
283 | } |
284 | 284 | ||
285 | 285 | ||
286 | /** Direct handoff |
286 | /** Direct handoff |
287 | * |
287 | * |
288 | * Direct handoff of reader/writer lock ownership |
288 | * Direct handoff of reader/writer lock ownership |
289 | * to waiting readers or a writer. |
289 | * to waiting readers or a writer. |
290 | * |
290 | * |
291 | * Must be called with rwl->lock locked. |
291 | * Must be called with rwl->lock locked. |
292 | * Must be called with interrupts_disable()'d. |
292 | * Must be called with interrupts_disable()'d. |
293 | * |
293 | * |
294 | * @param rwl Reader/Writer lock. |
294 | * @param rwl Reader/Writer lock. |
295 | * @param readers_only See the description below. |
295 | * @param readers_only See the description below. |
296 | * |
296 | * |
297 | * If readers_only is false: (unlock scenario) |
297 | * If readers_only is false: (unlock scenario) |
298 | * Let the first sleeper on 'exclusive' mutex in, no matter |
298 | * Let the first sleeper on 'exclusive' mutex in, no matter |
299 | * whether it is a reader or a writer. If there are more leading |
299 | * whether it is a reader or a writer. If there are more leading |
300 | * readers in line, let each of them in. |
300 | * readers in line, let each of them in. |
301 | * |
301 | * |
302 | * Otherwise: (timeout scenario) |
302 | * Otherwise: (timeout scenario) |
303 | * Let all leading readers in. |
303 | * Let all leading readers in. |
304 | */ |
304 | */ |
305 | void let_others_in(rwlock_t *rwl, int readers_only) |
305 | void let_others_in(rwlock_t *rwl, int readers_only) |
306 | { |
306 | { |
307 | rwlock_type_t type = RWLOCK_NONE; |
307 | rwlock_type_t type = RWLOCK_NONE; |
308 | thread_t *t = NULL; |
308 | thread_t *t = NULL; |
309 | int one_more = 1; |
309 | int one_more = 1; |
310 | 310 | ||
311 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
311 | spinlock_lock(&rwl->exclusive.sem.wq.lock); |
312 | 312 | ||
313 | if (!list_empty(&rwl->exclusive.sem.wq.head)) |
313 | if (!list_empty(&rwl->exclusive.sem.wq.head)) |
314 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link); |
314 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link); |
315 | do { |
315 | do { |
316 | if (t) { |
316 | if (t) { |
317 | spinlock_lock(&t->lock); |
317 | spinlock_lock(&t->lock); |
318 | type = t->rwlock_holder_type; |
318 | type = t->rwlock_holder_type; |
319 | spinlock_unlock(&t->lock); |
319 | spinlock_unlock(&t->lock); |
320 | } |
320 | } |
321 | 321 | ||
322 | /* |
322 | /* |
323 | * If readers_only is true, we wake all leading readers |
323 | * If readers_only is true, we wake all leading readers |
324 | * if and only if rwl is locked by another reader. |
324 | * if and only if rwl is locked by another reader. |
325 | * Assumption: readers_only ==> rwl->readers_in |
325 | * Assumption: readers_only ==> rwl->readers_in |
326 | */ |
326 | */ |
327 | if (readers_only && (type != RWLOCK_READER)) |
327 | if (readers_only && (type != RWLOCK_READER)) |
328 | break; |
328 | break; |
329 | 329 | ||
330 | 330 | ||
331 | if (type == RWLOCK_READER) { |
331 | if (type == RWLOCK_READER) { |
332 | /* |
332 | /* |
333 | * Waking up a reader. |
333 | * Waking up a reader. |
334 | * We are responsible for incrementing rwl->readers_in for it. |
334 | * We are responsible for incrementing rwl->readers_in for it. |
335 | */ |
335 | */ |
336 | rwl->readers_in++; |
336 | rwl->readers_in++; |
337 | } |
337 | } |
338 | 338 | ||
339 | /* |
339 | /* |
340 | * Only the last iteration through this loop can increment |
340 | * Only the last iteration through this loop can increment |
341 | * rwl->exclusive.sem.wq.missed_wakeup's. All preceeding |
341 | * rwl->exclusive.sem.wq.missed_wakeup's. All preceeding |
342 | * iterations will wake up a thread. |
342 | * iterations will wake up a thread. |
343 | */ |
343 | */ |
344 | /* We call the internal version of waitq_wakeup, which |
344 | /* We call the internal version of waitq_wakeup, which |
345 | * relies on the fact that the waitq is already locked. |
345 | * relies on the fact that the waitq is already locked. |
346 | */ |
346 | */ |
347 | _waitq_wakeup_unsafe(&rwl->exclusive.sem.wq, WAKEUP_FIRST); |
347 | _waitq_wakeup_unsafe(&rwl->exclusive.sem.wq, WAKEUP_FIRST); |
348 | 348 | ||
349 | t = NULL; |
349 | t = NULL; |
350 | if (!list_empty(&rwl->exclusive.sem.wq.head)) { |
350 | if (!list_empty(&rwl->exclusive.sem.wq.head)) { |
351 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link); |
351 | t = list_get_instance(rwl->exclusive.sem.wq.head.next, thread_t, wq_link); |
352 | if (t) { |
352 | if (t) { |
353 | spinlock_lock(&t->lock); |
353 | spinlock_lock(&t->lock); |
354 | if (t->rwlock_holder_type != RWLOCK_READER) |
354 | if (t->rwlock_holder_type != RWLOCK_READER) |
355 | one_more = 0; |
355 | one_more = 0; |
356 | spinlock_unlock(&t->lock); |
356 | spinlock_unlock(&t->lock); |
357 | } |
357 | } |
358 | } |
358 | } |
359 | } while ((type == RWLOCK_READER) && t && one_more); |
359 | } while ((type == RWLOCK_READER) && t && one_more); |
360 | 360 | ||
361 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
361 | spinlock_unlock(&rwl->exclusive.sem.wq.lock); |
362 | } |
362 | } |
363 | 363 | ||
364 | /** Release spinlock callback |
364 | /** Release spinlock callback |
365 | * |
365 | * |
366 | * This is a callback function invoked from the scheduler. |
366 | * This is a callback function invoked from the scheduler. |
367 | * The callback is registered in _rwlock_read_lock_timeout(). |
367 | * The callback is registered in _rwlock_read_lock_timeout(). |
368 | * |
368 | * |
369 | * @param arg Spinlock. |
369 | * @param arg Spinlock. |
370 | */ |
370 | */ |
371 | void release_spinlock(void *arg) |
371 | void release_spinlock(void *arg) |
372 | { |
372 | { |
373 | spinlock_unlock((spinlock_t *) arg); |
373 | spinlock_unlock((spinlock_t *) arg); |
374 | } |
374 | } |
375 | 375 |