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/*
*
* Copyright 2016, Google Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
#include "src/core/lib/support/mpscq.h"
#include <grpc/support/log.h>
void gpr_mpscq_init(gpr_mpscq *q) {
gpr_atm_no_barrier_store(&q->head, (gpr_atm)&q->stub);
q->tail = &q->stub;
gpr_atm_no_barrier_store(&q->stub.next, (gpr_atm)NULL);
}
void gpr_mpscq_destroy(gpr_mpscq *q) {
GPR_ASSERT(gpr_atm_no_barrier_load(&q->head) == (gpr_atm)&q->stub);
GPR_ASSERT(q->tail == &q->stub);
}
void gpr_mpscq_push(gpr_mpscq *q, gpr_mpscq_node *n) {
gpr_atm_no_barrier_store(&n->next, (gpr_atm)NULL);
gpr_mpscq_node *prev =
(gpr_mpscq_node *)gpr_atm_full_xchg(&q->head, (gpr_atm)n);
gpr_atm_rel_store(&prev->next, (gpr_atm)n);
}
gpr_mpscq_node *gpr_mpscq_pop(gpr_mpscq *q) {
gpr_mpscq_node *tail = q->tail;
gpr_mpscq_node *next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
if (tail == &q->stub) {
// indicates the list is actually (ephemerally) empty
if (next == NULL) return NULL;
q->tail = next;
tail = next;
next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
}
if (next != NULL) {
q->tail = next;
return tail;
}
gpr_mpscq_node *head = (gpr_mpscq_node *)gpr_atm_acq_load(&q->head);
if (tail != head) {
// indicates a retry is in order: we're still adding
return NULL;
}
gpr_mpscq_push(q, &q->stub);
next = (gpr_mpscq_node *)gpr_atm_acq_load(&tail->next);
if (next != NULL) {
q->tail = next;
return tail;
}
// indicates a retry is in order: we're still adding
return NULL;
}
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