1 /* 2 * 3 * Copyright 2015 gRPC authors. 4 * 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 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 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. 16 * 17 */ 18 19 #ifndef GRPC_SUPPORT_SYNC_H 20 #define GRPC_SUPPORT_SYNC_H 21 22 #include <grpc/support/port_platform.h> 23 24 #include <grpc/impl/codegen/gpr_types.h> /* for gpr_timespec */ 25 #include <grpc/impl/codegen/sync.h> 26 27 #ifdef __cplusplus 28 extern "C" { 29 #endif 30 31 /** --- Mutex interface --- 32 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. */ 37 38 /** Initialize *mu. Requires: *mu uninitialized. */ 39 GPRAPI void gpr_mu_init(gpr_mu* mu); 40 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); 44 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); 49 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); 53 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); 59 60 /** --- Condition variable interface --- 61 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. */ 65 66 /** Initialize *cv. Requires: *cv uninitialized. */ 67 GPRAPI void gpr_cv_init(gpr_cv* cv); 68 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); 72 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); 81 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); 87 88 /** Wake all threads waiting on *cv. Requires: *cv initialized. */ 89 GPRAPI void gpr_cv_broadcast(gpr_cv* cv); 90 91 /** --- One-time initialization --- 92 93 gpr_once must be declared with static storage class, and initialized with 94 GPR_ONCE_INIT. e.g., 95 static gpr_once once_var = GPR_ONCE_INIT; */ 96 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 101 finishes.*/ 102 GPRAPI void gpr_once_init(gpr_once* once, void (*init_routine)(void)); 103 104 /** --- One-time event notification --- 105 106 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. */ 110 111 /** Initialize *ev. */ 112 GPRAPI void gpr_event_init(gpr_event* ev); 113 114 /** 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); 118 119 /** 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); 125 126 /** 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); 132 133 /** --- Reference counting --- 134 135 These calls act on the type gpr_refcount. It requires no destruction. */ 136 137 /** Initialize *r to value n. */ 138 GPRAPI void gpr_ref_init(gpr_refcount* r, int n); 139 140 /** Increment the reference count *r. Requires *r initialized. */ 141 GPRAPI void gpr_ref(gpr_refcount* r); 142 143 /** Increment the reference count *r. Requires *r initialized. 144 Crashes if refcount is zero */ 145 GPRAPI void gpr_ref_non_zero(gpr_refcount* r); 146 147 /** Increment the reference count *r by n. Requires *r initialized, n > 0. */ 148 GPRAPI void gpr_refn(gpr_refcount* r, int n); 149 150 /** 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); 153 154 /** 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); 157 158 /** --- Stats counters --- 159 160 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. */ 165 166 /** Initialize *c to the value n. */ 167 GPRAPI void gpr_stats_init(gpr_stats_counter* c, intptr_t n); 168 169 /** *c += inc. Requires: *c initialized. */ 170 GPRAPI void gpr_stats_inc(gpr_stats_counter* c, intptr_t inc); 171 172 /** Return *c. Requires: *c initialized. */ 173 GPRAPI intptr_t gpr_stats_read(const gpr_stats_counter* c); 174 175 /** ==================Example use of interface=================== 176 A producer-consumer queue of up to N integers, 177 illustrating the use of the calls in this interface. */ 178 #if 0 179 180 #define N 4 181 182 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. */ 192 } queue; 193 194 /* Initialize *q. */ 195 void queue_init(queue *q) { 196 gpr_mu_init(&q->mu); 197 gpr_cv_init(&q->non_empty); 198 gpr_cv_init(&q->non_full); 199 q->head = 0; 200 q->length = 0; 201 } 202 203 /* 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); 208 } 209 210 /* Wait until there is room in *q, then append x to *q. */ 211 void queue_append(queue *q, int x) { 212 gpr_mu_lock(&q->mu); 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); 221 } 222 if (q->length == 0) { /* Wake threads blocked in queue_remove(). */ 223 /* It's normal to use gpr_cv_broadcast() or gpr_signal() while 224 holding the lock. */ 225 gpr_cv_broadcast(&q->non_empty); 226 } 227 q->elem[(q->head + q->length) % N] = x; 228 q->length++; 229 gpr_mu_unlock(&q->mu); 230 } 231 232 /* 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) { 235 int result = 0; 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); 240 } 241 q->elem[(q->head + q->length) % N] = x; 242 q->length++; 243 result = 1; 244 } 245 gpr_mu_unlock(&q->mu); 246 } 247 return result; 248 } 249 250 /* 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) { 254 int result = 0; 255 gpr_mu_lock(&q->mu); 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 260 lock. */ 261 while (q->length == 0 && 262 !gpr_cv_wait(&q->non_empty, &q->mu, abs_deadline)) { 263 } 264 if (q->length != 0) { /* Queue is non-empty. */ 265 result = 1; 266 if (q->length == N) { /* Wake threads blocked in queue_append(). */ 267 gpr_cv_broadcast(&q->non_full); 268 } 269 *head = q->elem[q->head]; 270 q->head = (q->head + 1) % N; 271 q->length--; 272 } /* else deadline exceeded */ 273 gpr_mu_unlock(&q->mu); 274 return result; 275 } 276 #endif /* 0 */ 277 278 #ifdef __cplusplus 279 } // extern "C" 280 #endif 281 282 #endif /* GRPC_SUPPORT_SYNC_H */ 283