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