7 #define RW_LOCK_BIAS 0x00100000
8 #define WRITE_LOCK_CMP RW_LOCK_BIAS
10 /** Example implementation of linux rw lock along with 2 thread test
15 1. At most 1 thread can acquire the write lock, and at the same time, no
16 other threads can acquire any lock (including read/write lock).
17 2. At most RW_LOCK_BIAS threads can successfully acquire the read lock.
18 3. A read_unlock release 1 read lock, and a write_unlock release the write
19 lock. They can not release a lock that they don't acquire.
21 4. Read_lock and write_lock can not be grabbed at the same time.
22 5. Happpens-before relationship should be checked and guaranteed, which
23 should be as the following:
24 a. read_unlock hb-> write_lock
25 b. write_unlock hb-> write_lock
26 c. write_unlock hb-> read_lock
30 Interesting point for locks:
31 a. If the users unlock() before any lock(), then the model checker will fail.
32 For this case, we can not say that the data structure is buggy, how can we
33 tell them from a real data structure bug???
34 b. We should specify that for a specific thread, successful locks and
35 unlocks should always come in pairs. We could make this check as an
36 auxiliary check since it is an extra rule for how the interfaces should called.
43 bool writer_lock_acquired;
46 writer_lock_acquired = false;
49 # Since commit_point_set has no ID attached, A -> B means that for any B,
50 # the previous A happens before B.
51 Read_Unlock -> Write_Lock
52 Read_Unlock -> Write_Trylock(HB_Write_Trylock_Succ)
54 Write_Unlock -> Write_Lock
55 Write_Unlock -> Write_Trylock(HB_Write_Trylock_Succ)
57 Write_Unlock -> Read_Lock
58 Write_Unlock -> Read_Trylock(HB_Read_Trylock_Succ)
69 static inline int read_can_lock(rwlock_t *lock)
71 return atomic_load_explicit(&lock->lock, memory_order_relaxed) > 0;
74 static inline int write_can_lock(rwlock_t *lock)
76 return atomic_load_explicit(&lock->lock, memory_order_relaxed) == RW_LOCK_BIAS;
84 Read_Lock_Success_1 | Read_Lock_Success_2
91 static inline void read_lock(rwlock_t *rw)
93 int priorvalue = atomic_fetch_sub_explicit(&rw->lock, 1, memory_order_acquire);
96 @Commit_point_define_check: __ATOMIC_RET__ > 0
97 @Label:Read_Lock_Success_1
100 while (priorvalue <= 0) {
101 atomic_fetch_add_explicit(&rw->lock, 1, memory_order_relaxed);
102 while (atomic_load_explicit(&rw->lock, memory_order_relaxed) <= 0) {
105 priorvalue = atomic_fetch_sub_explicit(&rw->lock, 1, memory_order_acquire);
108 @Commit_point_define_check: __ATOMIC_RET__ > 0
109 @Label:Read_Lock_Success_2
118 @Interface: Write_Lock
120 Write_Lock_Success_1 | Write_Lock_Success_2
122 !writer_lock_acquired && reader_lock_cnt == 0
124 writer_lock_acquired = true;
127 static inline void write_lock(rwlock_t *rw)
129 int priorvalue = atomic_fetch_sub_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_acquire);
132 @Commit_point_define_check: __ATOMIC_RET__ == RW_LOCK_BIAS
133 @Label: Write_Lock_Success_1
136 while (priorvalue != RW_LOCK_BIAS) {
137 atomic_fetch_add_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_relaxed);
138 while (atomic_load_explicit(&rw->lock, memory_order_relaxed) != RW_LOCK_BIAS) {
141 priorvalue = atomic_fetch_sub_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_acquire);
144 @Commit_point_define_check: __ATOMIC_RET__ == RW_LOCK_BIAS
145 @Label: Write_Lock_Success_2
153 @Interface: Read_Trylock
157 writer_lock_acquired == false
159 HB_Read_Trylock_Succ :: __RET__ == 1
164 __COND_SAT__ ? __RET__ == 1 : __RET__ == 0
167 static inline int read_trylock(rwlock_t *rw)
169 int priorvalue = atomic_fetch_sub_explicit(&rw->lock, 1, memory_order_acquire);
172 @Commit_point_define_check: true
173 @Label:Read_Trylock_Point
179 atomic_fetch_add_explicit(&rw->lock, 1, memory_order_relaxed);
185 @Interface: Write_Trylock
189 !writer_lock_acquired && reader_lock_cnt == 0
191 HB_Write_Trylock_Succ :: __RET__ == 1
194 writer_lock_acquired = true;
196 __COND_SAT__ ? __RET__ == 1 : __RET__ == 0
199 static inline int write_trylock(rwlock_t *rw)
201 int priorvalue = atomic_fetch_sub_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_acquire);
204 @Commit_point_define_check: true
205 @Label: Write_Trylock_Point
208 if (priorvalue == RW_LOCK_BIAS)
211 atomic_fetch_add_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_relaxed);
217 @Interface: Read_Unlock
218 @Commit_point_set: Read_Unlock_Point
220 reader_lock_cnt > 0 && !writer_lock_acquired
225 static inline void read_unlock(rwlock_t *rw)
227 atomic_fetch_add_explicit(&rw->lock, 1, memory_order_release);
230 @Commit_point_define_check: true
231 @Label: Read_Unlock_Point
238 @Interface: Write_Unlock
239 @Commit_point_set: Write_Unlock_Point
241 reader_lock_cnt == 0 && writer_lock_acquired
243 writer_lock_acquired = false;
247 static inline void write_unlock(rwlock_t *rw)
249 atomic_fetch_add_explicit(&rw->lock, RW_LOCK_BIAS, memory_order_release);
252 @Commit_point_define_check: true
253 @Label: Write_Unlock_Point
261 static void a(void *obj)
264 for(i = 0; i < 2; i++) {
267 load_32(&shareddata);
268 read_unlock(&mylock);
271 store_32(&shareddata,(unsigned int)i);
272 write_unlock(&mylock);
277 int user_main(int argc, char **argv)
280 atomic_init(&mylock.lock, RW_LOCK_BIAS);
282 thrd_create(&t1, (thrd_start_t)&a, NULL);
283 thrd_create(&t2, (thrd_start_t)&a, NULL);