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#pragma once
/*
http://www.1024cores.net/home/lock-free-algorithms/queues/non-intrusive-mpsc-node-based-queue
Simple semi-wait-free queue. Many producers - one consumer.
Tracking of allocated memory is not required.
No CAS. Only atomic swap (exchange) operations.
WARNING: a sleeping producer can stop progress for consumer.
WARNING: there is no wait¬ify mechanic for consumer,
consumer receives nullptr if queue was empty.
WARNING: the algorithm itself is lock-free
but producers and consumer could be blocked by memory allocator
Reference design: rtmapreduce/libs/threading/lfqueue.h
*/
#include <util/generic/noncopyable.h>
#include <util/system/types.h>
#include <util/system/atomic.h>
#include "tune.h"
namespace NThreading {
namespace NHTSwapPrivate {
template <typename T, typename TTuneup>
struct TNode
: public TTuneup::TNodeBase,
public TTuneup::template TNodeLayout<TNode<T, TTuneup>, T> {
TNode(const T& item) {
this->Next = nullptr;
this->Item = item;
}
TNode(T&& item) {
this->Next = nullptr;
this->Item = std::move(item);
}
};
struct TDefaultTuneup {
struct TNodeBase: private TNonCopyable {
};
template <typename TNode, typename T>
struct TNodeLayout {
TNode* Next;
T Item;
};
template <typename TNode>
struct TQueueLayout {
TNode* Head;
TNode* Tail;
};
};
template <typename T, typename TTuneup>
class THTSwapQueueImpl
: protected TTuneup::template TQueueLayout<TNode<T, TTuneup>> {
protected:
using TTunedNode = TNode<T, TTuneup>;
public:
using TItem = T;
THTSwapQueueImpl() {
this->Head = new TTunedNode(T());
this->Tail = this->Head;
}
~THTSwapQueueImpl() {
TTunedNode* node = this->Head;
while (node != nullptr) {
TTunedNode* next = node->Next;
delete node;
node = next;
}
}
template <typename TT>
void Push(TT&& item) {
Enqueue(new TTunedNode(std::forward<TT>(item)));
}
T Peek() {
TTunedNode* next = AtomicGet(this->Head->Next);
if (next == nullptr) {
return T();
}
return next->Item;
}
void Enqueue(TTunedNode* node) {
// our goal is to avoid expensive CAS here,
// but now consumer will be blocked until new tail linked.
// fortunately 'window of inconsistency' is extremely small.
TTunedNode* prev = AtomicSwap(&this->Tail, node);
AtomicSet(prev->Next, node);
}
T Pop() {
TTunedNode* next = AtomicGet(this->Head->Next);
if (next == nullptr) {
return nullptr;
}
auto item = std::move(next->Item);
std::swap(this->Head, next); // no need atomic here
delete next;
return item;
}
bool IsEmpty() const {
TTunedNode* next = AtomicGet(this->Head->Next);
return (next == nullptr);
}
};
}
DeclareTuneTypeParam(THTSwapNodeBase, TNodeBase);
DeclareTuneTypeParam(THTSwapNodeLayout, TNodeLayout);
DeclareTuneTypeParam(THTSwapQueueLayout, TQueueLayout);
template <typename T = void*, typename... TParams>
class THTSwapQueue
: public NHTSwapPrivate::THTSwapQueueImpl<T,
TTune<NHTSwapPrivate::TDefaultTuneup, TParams...>> {
};
}
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