| /* |
| * |
| * Copyright 2015 gRPC authors. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| * |
| */ |
| |
| #ifndef GRPC_SUPPORT_SYNC_H |
| #define GRPC_SUPPORT_SYNC_H |
| |
| #include <grpc/impl/codegen/gpr_types.h> /* for gpr_timespec */ |
| #include <grpc/impl/codegen/sync.h> |
| |
| #ifdef __cplusplus |
| extern "C" { |
| #endif |
| |
| /** --- Mutex interface --- |
| |
| At most one thread may hold an exclusive lock on a mutex at any given time. |
| Actions taken by a thread that holds a mutex exclusively happen after |
| actions taken by all previous holders of the mutex. Variables of type |
| gpr_mu are uninitialized when first declared. */ |
| |
| /** Initialize *mu. Requires: *mu uninitialized. */ |
| GPRAPI void gpr_mu_init(gpr_mu *mu); |
| |
| /** Cause *mu no longer to be initialized, freeing any memory in use. Requires: |
| *mu initialized; no other concurrent operation on *mu. */ |
| GPRAPI void gpr_mu_destroy(gpr_mu *mu); |
| |
| /** Wait until no thread has a lock on *mu, cause the calling thread to own an |
| exclusive lock on *mu, then return. May block indefinitely or crash if the |
| calling thread has a lock on *mu. Requires: *mu initialized. */ |
| GPRAPI void gpr_mu_lock(gpr_mu *mu); |
| |
| /** Release an exclusive lock on *mu held by the calling thread. Requires: *mu |
| initialized; the calling thread holds an exclusive lock on *mu. */ |
| GPRAPI void gpr_mu_unlock(gpr_mu *mu); |
| |
| /** Without blocking, attempt to acquire an exclusive lock on *mu for the |
| calling thread, then return non-zero iff success. Fail, if any thread holds |
| the lock; succeeds with high probability if no thread holds the lock. |
| Requires: *mu initialized. */ |
| GPRAPI int gpr_mu_trylock(gpr_mu *mu); |
| |
| /** --- Condition variable interface --- |
| |
| A while-loop should be used with gpr_cv_wait() when waiting for conditions |
| to become true. See the example below. Variables of type gpr_cv are |
| uninitialized when first declared. */ |
| |
| /** Initialize *cv. Requires: *cv uninitialized. */ |
| GPRAPI void gpr_cv_init(gpr_cv *cv); |
| |
| /** Cause *cv no longer to be initialized, freeing any memory in use. Requires: |
| *cv initialized; no other concurrent operation on *cv.*/ |
| GPRAPI void gpr_cv_destroy(gpr_cv *cv); |
| |
| /** Atomically release *mu and wait on *cv. When the calling thread is woken |
| from *cv or the deadline abs_deadline is exceeded, execute gpr_mu_lock(mu) |
| and return whether the deadline was exceeded. Use |
| abs_deadline==gpr_inf_future for no deadline. abs_deadline can be either |
| an absolute deadline, or a GPR_TIMESPAN. May return even when not |
| woken explicitly. Requires: *mu and *cv initialized; the calling thread |
| holds an exclusive lock on *mu. */ |
| GPRAPI int gpr_cv_wait(gpr_cv *cv, gpr_mu *mu, gpr_timespec abs_deadline); |
| |
| /** If any threads are waiting on *cv, wake at least one. |
| Clients may treat this as an optimization of gpr_cv_broadcast() |
| for use in the case where waking more than one waiter is not useful. |
| Requires: *cv initialized. */ |
| GPRAPI void gpr_cv_signal(gpr_cv *cv); |
| |
| /** Wake all threads waiting on *cv. Requires: *cv initialized. */ |
| GPRAPI void gpr_cv_broadcast(gpr_cv *cv); |
| |
| /** --- One-time initialization --- |
| |
| gpr_once must be declared with static storage class, and initialized with |
| GPR_ONCE_INIT. e.g., |
| static gpr_once once_var = GPR_ONCE_INIT; */ |
| |
| /** Ensure that (*init_routine)() has been called exactly once (for the |
| specified gpr_once instance) and then return. |
| If multiple threads call gpr_once() on the same gpr_once instance, one of |
| them will call (*init_routine)(), and the others will block until that call |
| finishes.*/ |
| GPRAPI void gpr_once_init(gpr_once *once, void (*init_routine)(void)); |
| |
| /** --- One-time event notification --- |
| |
| These operations act on a gpr_event, which should be initialized with |
| gpr_ev_init(), or with GPR_EVENT_INIT if static, e.g., |
| static gpr_event event_var = GPR_EVENT_INIT; |
| It requires no destruction. */ |
| |
| /** Initialize *ev. */ |
| GPRAPI void gpr_event_init(gpr_event *ev); |
| |
| /** Set *ev so that gpr_event_get() and gpr_event_wait() will return value. |
| Requires: *ev initialized; value != NULL; no prior or concurrent calls to |
| gpr_event_set(ev, ...) since initialization. */ |
| GPRAPI void gpr_event_set(gpr_event *ev, void *value); |
| |
| /** Return the value set by gpr_event_set(ev, ...), or NULL if no such call has |
| completed. If the result is non-NULL, all operations that occurred prior to |
| the gpr_event_set(ev, ...) set will be visible after this call returns. |
| Requires: *ev initialized. This operation is faster than acquiring a mutex |
| on most platforms. */ |
| GPRAPI void *gpr_event_get(gpr_event *ev); |
| |
| /** Wait until *ev is set by gpr_event_set(ev, ...), or abs_deadline is |
| exceeded, then return gpr_event_get(ev). Requires: *ev initialized. Use |
| abs_deadline==gpr_inf_future for no deadline. When the event has been |
| signalled before the call, this operation is faster than acquiring a mutex |
| on most platforms. */ |
| GPRAPI void *gpr_event_wait(gpr_event *ev, gpr_timespec abs_deadline); |
| |
| /** --- Reference counting --- |
| |
| These calls act on the type gpr_refcount. It requires no destruction. */ |
| |
| /** Initialize *r to value n. */ |
| GPRAPI void gpr_ref_init(gpr_refcount *r, int n); |
| |
| /** Increment the reference count *r. Requires *r initialized. */ |
| GPRAPI void gpr_ref(gpr_refcount *r); |
| |
| /** Increment the reference count *r. Requires *r initialized. |
| Crashes if refcount is zero */ |
| GPRAPI void gpr_ref_non_zero(gpr_refcount *r); |
| |
| /** Increment the reference count *r by n. Requires *r initialized, n > 0. */ |
| GPRAPI void gpr_refn(gpr_refcount *r, int n); |
| |
| /** Decrement the reference count *r and return non-zero iff it has reached |
| zero. . Requires *r initialized. */ |
| GPRAPI int gpr_unref(gpr_refcount *r); |
| |
| /** Return non-zero iff the reference count of *r is one, and thus is owned |
| by exactly one object. */ |
| GPRAPI int gpr_ref_is_unique(gpr_refcount *r); |
| |
| /** --- Stats counters --- |
| |
| These calls act on the integral type gpr_stats_counter. It requires no |
| destruction. Static instances may be initialized with |
| gpr_stats_counter c = GPR_STATS_INIT; |
| Beware: These operations do not imply memory barriers. Do not use them to |
| synchronize other events. */ |
| |
| /** Initialize *c to the value n. */ |
| GPRAPI void gpr_stats_init(gpr_stats_counter *c, intptr_t n); |
| |
| /** *c += inc. Requires: *c initialized. */ |
| GPRAPI void gpr_stats_inc(gpr_stats_counter *c, intptr_t inc); |
| |
| /** Return *c. Requires: *c initialized. */ |
| GPRAPI intptr_t gpr_stats_read(const gpr_stats_counter *c); |
| |
| /** ==================Example use of interface=================== |
| A producer-consumer queue of up to N integers, |
| illustrating the use of the calls in this interface. */ |
| #if 0 |
| |
| #define N 4 |
| |
| typedef struct queue { |
| gpr_cv non_empty; /* Signalled when length becomes non-zero. */ |
| gpr_cv non_full; /* Signalled when length becomes non-N. */ |
| gpr_mu mu; /* Protects all fields below. |
| (That is, except during initialization or |
| destruction, the fields below should be accessed |
| only by a thread that holds mu.) */ |
| int head; /* Index of head of queue 0..N-1. */ |
| int length; /* Number of valid elements in queue 0..N. */ |
| int elem[N]; /* elem[head .. head+length-1] are queue elements. */ |
| } queue; |
| |
| /* Initialize *q. */ |
| void queue_init(queue *q) { |
| gpr_mu_init(&q->mu); |
| gpr_cv_init(&q->non_empty); |
| gpr_cv_init(&q->non_full); |
| q->head = 0; |
| q->length = 0; |
| } |
| |
| /* Free storage associated with *q. */ |
| void queue_destroy(queue *q) { |
| gpr_mu_destroy(&q->mu); |
| gpr_cv_destroy(&q->non_empty); |
| gpr_cv_destroy(&q->non_full); |
| } |
| |
| /* Wait until there is room in *q, then append x to *q. */ |
| void queue_append(queue *q, int x) { |
| gpr_mu_lock(&q->mu); |
| /* To wait for a predicate without a deadline, loop on the negation of the |
| predicate, and use gpr_cv_wait(..., gpr_inf_future) inside the loop |
| to release the lock, wait, and reacquire on each iteration. Code that |
| makes the condition true should use gpr_cv_broadcast() on the |
| corresponding condition variable. The predicate must be on state |
| protected by the lock. */ |
| while (q->length == N) { |
| gpr_cv_wait(&q->non_full, &q->mu, gpr_inf_future); |
| } |
| if (q->length == 0) { /* Wake threads blocked in queue_remove(). */ |
| /* It's normal to use gpr_cv_broadcast() or gpr_signal() while |
| holding the lock. */ |
| gpr_cv_broadcast(&q->non_empty); |
| } |
| q->elem[(q->head + q->length) % N] = x; |
| q->length++; |
| gpr_mu_unlock(&q->mu); |
| } |
| |
| /* If it can be done without blocking, append x to *q and return non-zero. |
| Otherwise return 0. */ |
| int queue_try_append(queue *q, int x) { |
| int result = 0; |
| if (gpr_mu_trylock(&q->mu)) { |
| if (q->length != N) { |
| if (q->length == 0) { /* Wake threads blocked in queue_remove(). */ |
| gpr_cv_broadcast(&q->non_empty); |
| } |
| q->elem[(q->head + q->length) % N] = x; |
| q->length++; |
| result = 1; |
| } |
| gpr_mu_unlock(&q->mu); |
| } |
| return result; |
| } |
| |
| /* Wait until the *q is non-empty or deadline abs_deadline passes. If the |
| queue is non-empty, remove its head entry, place it in *head, and return |
| non-zero. Otherwise return 0. */ |
| int queue_remove(queue *q, int *head, gpr_timespec abs_deadline) { |
| int result = 0; |
| gpr_mu_lock(&q->mu); |
| /* To wait for a predicate with a deadline, loop on the negation of the |
| predicate or until gpr_cv_wait() returns true. Code that makes |
| the condition true should use gpr_cv_broadcast() on the corresponding |
| condition variable. The predicate must be on state protected by the |
| lock. */ |
| while (q->length == 0 && |
| !gpr_cv_wait(&q->non_empty, &q->mu, abs_deadline)) { |
| } |
| if (q->length != 0) { /* Queue is non-empty. */ |
| result = 1; |
| if (q->length == N) { /* Wake threads blocked in queue_append(). */ |
| gpr_cv_broadcast(&q->non_full); |
| } |
| *head = q->elem[q->head]; |
| q->head = (q->head + 1) % N; |
| q->length--; |
| } /* else deadline exceeded */ |
| gpr_mu_unlock(&q->mu); |
| return result; |
| } |
| #endif /* 0 */ |
| |
| #ifdef __cplusplus |
| } // extern "C" |
| |
| namespace grpc_core { |
| |
| class mu_guard { |
| public: |
| mu_guard(gpr_mu *mu) : mu_(mu) { gpr_mu_lock(mu); } |
| ~mu_guard() { gpr_mu_unlock(mu_); } |
| |
| mu_guard(const mu_guard &) = delete; |
| mu_guard &operator=(const mu_guard &) = delete; |
| |
| private: |
| gpr_mu *const mu_; |
| }; |
| |
| } // namespace grpc_core |
| #endif |
| |
| #endif /* GRPC_SUPPORT_SYNC_H */ |