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#include "mpsc_intrusive_unordered.h"
#include <util/system/atomic.h>
namespace NThreading {
void TMPSCIntrusiveUnordered::Push(TIntrusiveNode* node) noexcept {
auto head = AtomicGet(HeadForCaS);
for (ui32 i = NUMBER_OF_TRIES_FOR_CAS; i-- > 0;) {
// no ABA here, because Next is exactly head
// it does not matter how many travels head was made/
node->Next = head;
auto prev = AtomicGetAndCas(&HeadForCaS, node, head);
if (head == prev) {
return;
}
head = prev;
}
// boring of trying to do cas, let's just swap
// no need for atomic here, because the next is atomic swap
node->Next = 0;
head = AtomicSwap(&HeadForSwap, node);
if (head != nullptr) {
AtomicSet(node->Next, head);
} else {
// consumer must know if no other thread may access the memory,
// setting Next to node is a way to notify consumer
AtomicSet(node->Next, node);
}
}
TIntrusiveNode* TMPSCIntrusiveUnordered::PopMany() noexcept {
if (NotReadyChain == nullptr) {
auto head = AtomicSwap(&HeadForSwap, nullptr);
NotReadyChain = head;
}
if (NotReadyChain != nullptr) {
auto next = AtomicGet(NotReadyChain->Next);
if (next != nullptr) {
auto ready = NotReadyChain;
TIntrusiveNode* cut;
do {
cut = NotReadyChain;
NotReadyChain = next;
next = AtomicGet(NotReadyChain->Next);
if (next == NotReadyChain) {
cut = NotReadyChain;
NotReadyChain = nullptr;
break;
}
} while (next != nullptr);
cut->Next = nullptr;
return ready;
}
}
if (AtomicGet(HeadForCaS) != nullptr) {
return AtomicSwap(&HeadForCaS, nullptr);
}
return nullptr;
}
TIntrusiveNode* TMPSCIntrusiveUnordered::Pop() noexcept {
if (PopOneQueue != nullptr) {
auto head = PopOneQueue;
PopOneQueue = PopOneQueue->Next;
return head;
}
PopOneQueue = PopMany();
if (PopOneQueue != nullptr) {
auto head = PopOneQueue;
PopOneQueue = PopOneQueue->Next;
return head;
}
return nullptr;
}
}
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