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//
// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2026
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#pragma once
#include "td/utils/common.h"
#include <atomic>
namespace td {
//NB: holder of the queue holds all responsibility of freeing its nodes
class MpscLinkQueueImpl {
public:
class Node;
class Reader;
void push(Node *node) {
node->next_ = head_.load(std::memory_order_relaxed);
while (!head_.compare_exchange_strong(node->next_, node, std::memory_order_release, std::memory_order_relaxed)) {
}
}
void push_unsafe(Node *node) {
node->next_ = head_.load(std::memory_order_relaxed);
head_.store(node, std::memory_order_relaxed);
}
void pop_all(Reader &reader) {
return reader.add(head_.exchange(nullptr, std::memory_order_acquire));
}
void pop_all_unsafe(Reader &reader) {
return reader.add(head_.exchange(nullptr, std::memory_order_relaxed));
}
class Node {
friend class MpscLinkQueueImpl;
Node *next_{nullptr};
};
class Reader {
public:
Node *read() {
auto old_head = head_;
if (head_) {
head_ = head_->next_;
}
return old_head;
}
void delay(Node *node) {
node->next_ = head_;
if (!head_) {
tail_ = node;
}
head_ = node;
}
size_t calc_size() const {
size_t res = 0;
for (auto it = head_; it != nullptr; it = it->next_, res++) {
}
return res;
}
private:
friend class MpscLinkQueueImpl;
void add(Node *node) {
if (node == nullptr) {
return;
}
// Reverse list
Node *tail = node;
Node *head = nullptr;
while (node) {
auto next = node->next_;
node->next_ = head;
head = node;
node = next;
}
if (head_ == nullptr) {
head_ = head;
} else {
tail_->next_ = head;
}
tail_ = tail;
}
Node *head_{nullptr};
Node *tail_{nullptr};
};
private:
std::atomic<Node *> head_{nullptr};
};
// Uses MpscLinkQueueImpl.
// Node should have to_mpsc_link_queue_node and from_mpsc_link_queue_node functions
template <class Node>
class MpscLinkQueue {
public:
void push(Node node) {
impl_.push(node.to_mpsc_link_queue_node());
}
void push_unsafe(Node node) {
impl_.push_unsafe(node.to_mpsc_link_queue_node());
}
class Reader {
public:
~Reader() {
CHECK(!read());
}
Node read() {
auto node = impl_.read();
if (!node) {
return {};
}
return Node::from_mpsc_link_queue_node(node);
}
void delay(Node node) {
impl_.delay(node.to_mpsc_link_queue_node());
}
size_t calc_size() const {
return impl_.calc_size();
}
private:
friend class MpscLinkQueue;
MpscLinkQueueImpl::Reader impl_;
MpscLinkQueueImpl::Reader &impl() {
return impl_;
}
};
void pop_all(Reader &reader) {
return impl_.pop_all(reader.impl());
}
void pop_all_unsafe(Reader &reader) {
return impl_.pop_all_unsafe(reader.impl());
}
private:
MpscLinkQueueImpl impl_;
};
template <class Value>
class MpscLinkQueueUniquePtrNode {
public:
MpscLinkQueueUniquePtrNode() = default;
explicit MpscLinkQueueUniquePtrNode(unique_ptr<Value> ptr) : ptr_(std::move(ptr)) {
}
MpscLinkQueueImpl::Node *to_mpsc_link_queue_node() {
return ptr_.release()->to_mpsc_link_queue_node();
}
static MpscLinkQueueUniquePtrNode<Value> from_mpsc_link_queue_node(MpscLinkQueueImpl::Node *node) {
return MpscLinkQueueUniquePtrNode<Value>(unique_ptr<Value>(Value::from_mpsc_link_queue_node(node)));
}
explicit operator bool() const noexcept {
return ptr_ != nullptr;
}
Value &value() {
return *ptr_;
}
private:
unique_ptr<Value> ptr_;
};
} // namespace td
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