third_party/grpc/src/core/lib/gpr/mpscq.cc

/*
 *
 * 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 <grpc/support/port_platform.h>

#include "src/core/lib/gpr/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);
}

bool 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);
  return prev == &q->stub;
}

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 == nullptr) {
      *empty = true;
      return nullptr;
    }
    q->tail = next;
    tail = next;
    next = (gpr_mpscq_node*)gpr_atm_acq_load(&tail->next);
  }
  if (next != nullptr) {
    *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 nullptr;
  }
  gpr_mpscq_push(q, &q->stub);
  next = (gpr_mpscq_node*)gpr_atm_acq_load(&tail->next);
  if (next != nullptr) {
    *empty = false;
    q->tail = next;
    return tail;
  }
  // indicates a retry is in order: we're still adding
  *empty = false;
  return nullptr;
}

void gpr_locked_mpscq_init(gpr_locked_mpscq* q) {
  gpr_mpscq_init(&q->queue);
  gpr_mu_init(&q->mu);
}

void gpr_locked_mpscq_destroy(gpr_locked_mpscq* q) {
  gpr_mpscq_destroy(&q->queue);
  gpr_mu_destroy(&q->mu);
}

bool gpr_locked_mpscq_push(gpr_locked_mpscq* q, gpr_mpscq_node* n) {
  return gpr_mpscq_push(&q->queue, n);
}

gpr_mpscq_node* gpr_locked_mpscq_try_pop(gpr_locked_mpscq* q) {
  if (gpr_mu_trylock(&q->mu)) {
    gpr_mpscq_node* n = gpr_mpscq_pop(&q->queue);
    gpr_mu_unlock(&q->mu);
    return n;
  }
  return nullptr;
}

gpr_mpscq_node* gpr_locked_mpscq_pop(gpr_locked_mpscq* q) {
  gpr_mu_lock(&q->mu);
  bool empty = false;
  gpr_mpscq_node* n;
  do {
    n = gpr_mpscq_pop_and_check_end(&q->queue, &empty);
  } while (n == nullptr && !empty);
  gpr_mu_unlock(&q->mu);
  return n;
}