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/*
*
* Copyright 2016 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.
*
*/
#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) {
bool empty;
return gpr_mpscq_pop_and_check_end(q, &empty);
}
gpr_mpscq_node* gpr_mpscq_pop_and_check_end(gpr_mpscq* q, bool* empty) {
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) {
*empty = true;
return NULL;
}
q->tail = next;
tail = next;
next = (gpr_mpscq_node*)gpr_atm_acq_load(&tail->next);
}
if (next != NULL) {
*empty = false;
q->tail = next;
return tail;
}
gpr_mpscq_node* head = (gpr_mpscq_node*)gpr_atm_acq_load(&q->head);
if (tail != head) {
*empty = false;
// 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
*empty = false;
return NULL;
}
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