3 * Copyright 2015 gRPC authors.
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
9 * http://www.apache.org/licenses/LICENSE-2.0
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
19 #ifndef GRPC_SUPPORT_SYNC_H
20 #define GRPC_SUPPORT_SYNC_H
22 #include <grpc/support/port_platform.h>
24 #include <grpc/impl/codegen/gpr_types.h> /* for gpr_timespec */
25 #include <grpc/impl/codegen/sync.h>
31 /** --- Mutex interface ---
33 At most one thread may hold an exclusive lock on a mutex at any given time.
34 Actions taken by a thread that holds a mutex exclusively happen after
35 actions taken by all previous holders of the mutex. Variables of type
36 gpr_mu are uninitialized when first declared. */
38 /** Initialize *mu. Requires: *mu uninitialized. */
39 GPRAPI void gpr_mu_init(gpr_mu* mu);
41 /** Cause *mu no longer to be initialized, freeing any memory in use. Requires:
42 *mu initialized; no other concurrent operation on *mu. */
43 GPRAPI void gpr_mu_destroy(gpr_mu* mu);
45 /** Wait until no thread has a lock on *mu, cause the calling thread to own an
46 exclusive lock on *mu, then return. May block indefinitely or crash if the
47 calling thread has a lock on *mu. Requires: *mu initialized. */
48 GPRAPI void gpr_mu_lock(gpr_mu* mu);
50 /** Release an exclusive lock on *mu held by the calling thread. Requires: *mu
51 initialized; the calling thread holds an exclusive lock on *mu. */
52 GPRAPI void gpr_mu_unlock(gpr_mu* mu);
54 /** Without blocking, attempt to acquire an exclusive lock on *mu for the
55 calling thread, then return non-zero iff success. Fail, if any thread holds
56 the lock; succeeds with high probability if no thread holds the lock.
57 Requires: *mu initialized. */
58 GPRAPI int gpr_mu_trylock(gpr_mu* mu);
60 /** --- Condition variable interface ---
62 A while-loop should be used with gpr_cv_wait() when waiting for conditions
63 to become true. See the example below. Variables of type gpr_cv are
64 uninitialized when first declared. */
66 /** Initialize *cv. Requires: *cv uninitialized. */
67 GPRAPI void gpr_cv_init(gpr_cv* cv);
69 /** Cause *cv no longer to be initialized, freeing any memory in use. Requires:
70 *cv initialized; no other concurrent operation on *cv.*/
71 GPRAPI void gpr_cv_destroy(gpr_cv* cv);
73 /** Atomically release *mu and wait on *cv. When the calling thread is woken
74 from *cv or the deadline abs_deadline is exceeded, execute gpr_mu_lock(mu)
75 and return whether the deadline was exceeded. Use
76 abs_deadline==gpr_inf_future for no deadline. abs_deadline can be either
77 an absolute deadline, or a GPR_TIMESPAN. May return even when not
78 woken explicitly. Requires: *mu and *cv initialized; the calling thread
79 holds an exclusive lock on *mu. */
80 GPRAPI int gpr_cv_wait(gpr_cv* cv, gpr_mu* mu, gpr_timespec abs_deadline);
82 /** If any threads are waiting on *cv, wake at least one.
83 Clients may treat this as an optimization of gpr_cv_broadcast()
84 for use in the case where waking more than one waiter is not useful.
85 Requires: *cv initialized. */
86 GPRAPI void gpr_cv_signal(gpr_cv* cv);
88 /** Wake all threads waiting on *cv. Requires: *cv initialized. */
89 GPRAPI void gpr_cv_broadcast(gpr_cv* cv);
91 /** --- One-time initialization ---
93 gpr_once must be declared with static storage class, and initialized with
95 static gpr_once once_var = GPR_ONCE_INIT; */
97 /** Ensure that (*init_routine)() has been called exactly once (for the
98 specified gpr_once instance) and then return.
99 If multiple threads call gpr_once() on the same gpr_once instance, one of
100 them will call (*init_routine)(), and the others will block until that call
102 GPRAPI void gpr_once_init(gpr_once* once, void (*init_routine)(void));
104 /** --- One-time event notification ---
106 These operations act on a gpr_event, which should be initialized with
107 gpr_ev_init(), or with GPR_EVENT_INIT if static, e.g.,
108 static gpr_event event_var = GPR_EVENT_INIT;
109 It requires no destruction. */
111 /** Initialize *ev. */
112 GPRAPI void gpr_event_init(gpr_event* ev);
114 /** Set *ev so that gpr_event_get() and gpr_event_wait() will return value.
115 Requires: *ev initialized; value != NULL; no prior or concurrent calls to
116 gpr_event_set(ev, ...) since initialization. */
117 GPRAPI void gpr_event_set(gpr_event* ev, void* value);
119 /** Return the value set by gpr_event_set(ev, ...), or NULL if no such call has
120 completed. If the result is non-NULL, all operations that occurred prior to
121 the gpr_event_set(ev, ...) set will be visible after this call returns.
122 Requires: *ev initialized. This operation is faster than acquiring a mutex
123 on most platforms. */
124 GPRAPI void* gpr_event_get(gpr_event* ev);
126 /** Wait until *ev is set by gpr_event_set(ev, ...), or abs_deadline is
127 exceeded, then return gpr_event_get(ev). Requires: *ev initialized. Use
128 abs_deadline==gpr_inf_future for no deadline. When the event has been
129 signalled before the call, this operation is faster than acquiring a mutex
130 on most platforms. */
131 GPRAPI void* gpr_event_wait(gpr_event* ev, gpr_timespec abs_deadline);
133 /** --- Reference counting ---
135 These calls act on the type gpr_refcount. It requires no destruction. */
137 /** Initialize *r to value n. */
138 GPRAPI void gpr_ref_init(gpr_refcount* r, int n);
140 /** Increment the reference count *r. Requires *r initialized. */
141 GPRAPI void gpr_ref(gpr_refcount* r);
143 /** Increment the reference count *r. Requires *r initialized.
144 Crashes if refcount is zero */
145 GPRAPI void gpr_ref_non_zero(gpr_refcount* r);
147 /** Increment the reference count *r by n. Requires *r initialized, n > 0. */
148 GPRAPI void gpr_refn(gpr_refcount* r, int n);
150 /** Decrement the reference count *r and return non-zero iff it has reached
151 zero. . Requires *r initialized. */
152 GPRAPI int gpr_unref(gpr_refcount* r);
154 /** Return non-zero iff the reference count of *r is one, and thus is owned
155 by exactly one object. */
156 GPRAPI int gpr_ref_is_unique(gpr_refcount* r);
158 /** --- Stats counters ---
160 These calls act on the integral type gpr_stats_counter. It requires no
161 destruction. Static instances may be initialized with
162 gpr_stats_counter c = GPR_STATS_INIT;
163 Beware: These operations do not imply memory barriers. Do not use them to
164 synchronize other events. */
166 /** Initialize *c to the value n. */
167 GPRAPI void gpr_stats_init(gpr_stats_counter* c, intptr_t n);
169 /** *c += inc. Requires: *c initialized. */
170 GPRAPI void gpr_stats_inc(gpr_stats_counter* c, intptr_t inc);
172 /** Return *c. Requires: *c initialized. */
173 GPRAPI intptr_t gpr_stats_read(const gpr_stats_counter* c);
175 /** ==================Example use of interface===================
176 A producer-consumer queue of up to N integers,
177 illustrating the use of the calls in this interface. */
182 typedef struct queue {
183 gpr_cv non_empty; /* Signalled when length becomes non-zero. */
184 gpr_cv non_full; /* Signalled when length becomes non-N. */
185 gpr_mu mu; /* Protects all fields below.
186 (That is, except during initialization or
187 destruction, the fields below should be accessed
188 only by a thread that holds mu.) */
189 int head; /* Index of head of queue 0..N-1. */
190 int length; /* Number of valid elements in queue 0..N. */
191 int elem[N]; /* elem[head .. head+length-1] are queue elements. */
195 void queue_init(queue *q) {
197 gpr_cv_init(&q->non_empty);
198 gpr_cv_init(&q->non_full);
203 /* Free storage associated with *q. */
204 void queue_destroy(queue *q) {
205 gpr_mu_destroy(&q->mu);
206 gpr_cv_destroy(&q->non_empty);
207 gpr_cv_destroy(&q->non_full);
210 /* Wait until there is room in *q, then append x to *q. */
211 void queue_append(queue *q, int x) {
213 /* To wait for a predicate without a deadline, loop on the negation of the
214 predicate, and use gpr_cv_wait(..., gpr_inf_future) inside the loop
215 to release the lock, wait, and reacquire on each iteration. Code that
216 makes the condition true should use gpr_cv_broadcast() on the
217 corresponding condition variable. The predicate must be on state
218 protected by the lock. */
219 while (q->length == N) {
220 gpr_cv_wait(&q->non_full, &q->mu, gpr_inf_future);
222 if (q->length == 0) { /* Wake threads blocked in queue_remove(). */
223 /* It's normal to use gpr_cv_broadcast() or gpr_signal() while
225 gpr_cv_broadcast(&q->non_empty);
227 q->elem[(q->head + q->length) % N] = x;
229 gpr_mu_unlock(&q->mu);
232 /* If it can be done without blocking, append x to *q and return non-zero.
233 Otherwise return 0. */
234 int queue_try_append(queue *q, int x) {
236 if (gpr_mu_trylock(&q->mu)) {
237 if (q->length != N) {
238 if (q->length == 0) { /* Wake threads blocked in queue_remove(). */
239 gpr_cv_broadcast(&q->non_empty);
241 q->elem[(q->head + q->length) % N] = x;
245 gpr_mu_unlock(&q->mu);
250 /* Wait until the *q is non-empty or deadline abs_deadline passes. If the
251 queue is non-empty, remove its head entry, place it in *head, and return
252 non-zero. Otherwise return 0. */
253 int queue_remove(queue *q, int *head, gpr_timespec abs_deadline) {
256 /* To wait for a predicate with a deadline, loop on the negation of the
257 predicate or until gpr_cv_wait() returns true. Code that makes
258 the condition true should use gpr_cv_broadcast() on the corresponding
259 condition variable. The predicate must be on state protected by the
261 while (q->length == 0 &&
262 !gpr_cv_wait(&q->non_empty, &q->mu, abs_deadline)) {
264 if (q->length != 0) { /* Queue is non-empty. */
266 if (q->length == N) { /* Wake threads blocked in queue_append(). */
267 gpr_cv_broadcast(&q->non_full);
269 *head = q->elem[q->head];
270 q->head = (q->head + 1) % N;
272 } /* else deadline exceeded */
273 gpr_mu_unlock(&q->mu);
282 #endif /* GRPC_SUPPORT_SYNC_H */