/*
*
* 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/support/port_platform.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"
#endif
#endif /* GRPC_SUPPORT_SYNC_H */