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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.
//
//
#ifndef GRPC_SRC_CORE_LIB_GPRPP_MPSCQ_H
#define GRPC_SRC_CORE_LIB_GPRPP_MPSCQ_H
#include <grpc/support/port_platform.h>
#include <atomic>
#include <grpc/support/log.h>
#include "src/core/lib/gprpp/sync.h"
namespace grpc_core {
// Multiple-producer single-consumer lock free queue, based upon the
// implementation from Dmitry Vyukov here:
// http://www.1024cores.net/home/lock-free-algorithms/queues/intrusive-mpsc-node-based-queue
class MultiProducerSingleConsumerQueue {
public:
// List node. Application node types can inherit from this.
struct Node {
std::atomic<Node*> next{nullptr};
};
MultiProducerSingleConsumerQueue() : head_{&stub_}, tail_(&stub_) {}
~MultiProducerSingleConsumerQueue() {
GPR_ASSERT(head_.load(std::memory_order_relaxed) == &stub_);
GPR_ASSERT(tail_ == &stub_);
}
// Push a node
// Thread safe - can be called from multiple threads concurrently
// Returns true if this was possibly the first node (may return true
// sporadically, will not return false sporadically)
bool Push(Node* node);
// Pop a node (returns NULL if no node is ready - which doesn't indicate that
// the queue is empty!!)
// Thread compatible - can only be called from one thread at a time
Node* Pop();
// Pop a node; sets *empty to true if the queue is empty, or false if it is
// not.
Node* PopAndCheckEnd(bool* empty);
private:
// make sure head & tail don't share a cacheline
union {
char padding_[GPR_CACHELINE_SIZE];
std::atomic<Node*> head_{nullptr};
};
Node* tail_;
Node stub_;
};
// An mpscq with a lock: it's safe to pop from multiple threads, but doing
// only one thread will succeed concurrently.
class LockedMultiProducerSingleConsumerQueue {
public:
typedef MultiProducerSingleConsumerQueue::Node Node;
// Push a node
// Thread safe - can be called from multiple threads concurrently
// Returns true if this was possibly the first node (may return true
// sporadically, will not return false sporadically)
bool Push(Node* node);
// Pop a node (returns NULL if no node is ready - which doesn't indicate that
// the queue is empty!!)
// Thread safe - can be called from multiple threads concurrently
Node* TryPop();
// Pop a node. Returns NULL only if the queue was empty at some point after
// calling this function
Node* Pop();
private:
MultiProducerSingleConsumerQueue queue_;
Mutex mu_;
};
} // namespace grpc_core
#endif // GRPC_SRC_CORE_LIB_GPRPP_MPSCQ_H
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