/* * * 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 #include /* for gpr_timespec */ #include #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" #endif #endif /* GRPC_SUPPORT_SYNC_H */