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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 <grpc/support/port_platform.h>
#include "src/core/lib/gprpp/mpscq.h"
namespace grpc_core {
//
// MultiProducerSingleConsumerQueue
//
bool MultiProducerSingleConsumerQueue::Push(Node* node) {
node->next.Store(nullptr, MemoryOrder::RELAXED);
Node* prev = head_.Exchange(node, MemoryOrder::ACQ_REL);
prev->next.Store(node, MemoryOrder::RELEASE);
return prev == &stub_;
}
MultiProducerSingleConsumerQueue::Node*
MultiProducerSingleConsumerQueue::Pop() {
bool empty;
return PopAndCheckEnd(&empty);
}
MultiProducerSingleConsumerQueue::Node*
MultiProducerSingleConsumerQueue::PopAndCheckEnd(bool* empty) {
Node* tail = tail_;
Node* next = tail_->next.Load(MemoryOrder::ACQUIRE);
if (tail == &stub_) {
// indicates the list is actually (ephemerally) empty
if (next == nullptr) {
*empty = true;
return nullptr;
}
tail_ = next;
tail = next;
next = tail->next.Load(MemoryOrder::ACQUIRE);
}
if (next != nullptr) {
*empty = false;
tail_ = next;
return tail;
}
Node* head = head_.Load(MemoryOrder::ACQUIRE);
if (tail != head) {
*empty = false;
// indicates a retry is in order: we're still adding
return nullptr;
}
Push(&stub_);
next = tail->next.Load(MemoryOrder::ACQUIRE);
if (next != nullptr) {
*empty = false;
tail_ = next;
return tail;
}
// indicates a retry is in order: we're still adding
*empty = false;
return nullptr;
}
//
// LockedMultiProducerSingleConsumerQueue
//
bool LockedMultiProducerSingleConsumerQueue::Push(Node* node) {
return queue_.Push(node);
}
LockedMultiProducerSingleConsumerQueue::Node*
LockedMultiProducerSingleConsumerQueue::TryPop() {
if (gpr_mu_trylock(mu_.get())) {
Node* node = queue_.Pop();
gpr_mu_unlock(mu_.get());
return node;
}
return nullptr;
}
LockedMultiProducerSingleConsumerQueue::Node*
LockedMultiProducerSingleConsumerQueue::Pop() {
MutexLock lock(&mu_);
bool empty = false;
Node* node;
do {
node = queue_.PopAndCheckEnd(&empty);
} while (node == nullptr && !empty);
return node;
}
} // namespace grpc_core
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