4 * Userspace RCU library
6 * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
8 * Distributed under GPLv2
20 pthread_mutex_t urcu_mutex
= PTHREAD_MUTEX_INITIALIZER
;
23 * Global grace period counter.
24 * Contains the current RCU_GP_CTR_BIT.
25 * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path.
27 long urcu_gp_ctr
= RCU_GP_COUNT
;
29 long __thread urcu_active_readers
;
31 /* Thread IDs of registered readers */
32 #define INIT_NUM_THREADS 4
36 long *urcu_active_readers
;
40 unsigned int yield_active
;
41 unsigned int __thread rand_yield
;
44 static struct reader_data
*reader_data
;
45 static int num_readers
, alloc_readers
;
48 void internal_urcu_lock(void)
51 ret
= pthread_mutex_lock(&urcu_mutex
);
53 perror("Error in pthread mutex lock");
58 void internal_urcu_unlock(void)
62 ret
= pthread_mutex_unlock(&urcu_mutex
);
64 perror("Error in pthread mutex unlock");
70 * called with urcu_mutex held.
72 static void switch_next_urcu_qparity(void)
74 urcu_gp_ctr
^= RCU_GP_CTR_BIT
;
78 static void force_mb_all_threads(void)
83 static void force_mb_all_threads(void)
85 struct reader_data
*index
;
87 * Ask for each threads to execute a mb() so we can consider the
88 * compiler barriers around rcu read lock as real memory barriers.
95 mb(); /* write sig_done before sending the signals */
97 for (index
= reader_data
; index
< reader_data
+ num_readers
; index
++) {
98 pthread_kill(index
->tid
, SIGURCU
);
102 * Wait for sighandler (and thus mb()) to execute on every thread.
105 while (sig_done
< num_readers
)
108 mb(); /* read sig_done before ending the barrier */
113 void wait_for_quiescent_state(void)
115 struct reader_data
*index
;
119 /* Wait for each thread urcu_active_readers count to become 0.
121 for (index
= reader_data
; index
< reader_data
+ num_readers
; index
++) {
125 while (rcu_old_gp_ongoing(index
->urcu_active_readers
))
129 * Locally : read *index->urcu_active_readers before freeing old
131 * Remote (reader threads) : Order urcu_qparity update and other
132 * thread's quiescent state counter read.
134 force_mb_all_threads();
137 static void switch_qparity(void)
139 /* All threads should read qparity before accessing data structure. */
140 /* Write ptr before changing the qparity */
141 force_mb_all_threads();
143 switch_next_urcu_qparity();
147 * Wait for previous parity to be empty of readers.
149 wait_for_quiescent_state();
152 void synchronize_rcu(void)
155 internal_urcu_lock();
161 internal_urcu_unlock();
165 void urcu_add_reader(pthread_t id
)
167 struct reader_data
*oldarray
;
170 alloc_readers
= INIT_NUM_THREADS
;
173 malloc(sizeof(struct reader_data
) * alloc_readers
);
175 if (alloc_readers
< num_readers
+ 1) {
176 oldarray
= reader_data
;
177 reader_data
= malloc(sizeof(struct reader_data
)
178 * (alloc_readers
<< 1));
179 memcpy(reader_data
, oldarray
,
180 sizeof(struct reader_data
) * alloc_readers
);
184 reader_data
[num_readers
].tid
= id
;
185 /* reference to the TLS of _this_ reader thread. */
186 reader_data
[num_readers
].urcu_active_readers
= &urcu_active_readers
;
191 * Never shrink (implementation limitation).
192 * This is O(nb threads). Eventually use a hash table.
194 void urcu_remove_reader(pthread_t id
)
196 struct reader_data
*index
;
198 assert(reader_data
!= NULL
);
199 for (index
= reader_data
; index
< reader_data
+ num_readers
; index
++) {
200 if (pthread_equal(index
->tid
, id
)) {
201 memcpy(index
, &reader_data
[num_readers
- 1],
202 sizeof(struct reader_data
));
203 reader_data
[num_readers
- 1].tid
= 0;
204 reader_data
[num_readers
- 1].urcu_active_readers
= NULL
;
209 /* Hrm not found, forgot to register ? */
213 void urcu_register_thread(void)
215 internal_urcu_lock();
216 urcu_add_reader(pthread_self());
217 internal_urcu_unlock();
220 void urcu_unregister_thread(void)
222 internal_urcu_lock();
223 urcu_remove_reader(pthread_self());
224 internal_urcu_unlock();
227 #ifndef DEBUG_FULL_MB
228 void sigurcu_handler(int signo
, siginfo_t
*siginfo
, void *context
)
231 atomic_inc(&sig_done
);
234 void __attribute__((constructor
)) urcu_init(void)
236 struct sigaction act
;
239 act
.sa_sigaction
= sigurcu_handler
;
240 ret
= sigaction(SIGURCU
, &act
, NULL
);
242 perror("Error in sigaction");
247 void __attribute__((destructor
)) urcu_exit(void)
249 struct sigaction act
;
252 ret
= sigaction(SIGURCU
, NULL
, &act
);
254 perror("Error in sigaction");
257 assert(act
.sa_sigaction
== sigurcu_handler
);