151 lines
3.6 KiB
Go
151 lines
3.6 KiB
Go
//go:build go1.19
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// +build go1.19
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package xsync
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import (
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"runtime"
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"sync/atomic"
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"unsafe"
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)
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// A MPMCQueueOf is a bounded multi-producer multi-consumer concurrent
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// queue. It's a generic version of MPMCQueue.
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//
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// MPMCQueue instances must be created with NewMPMCQueueOf function.
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// A MPMCQueueOf must not be copied after first use.
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//
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// Based on the data structure from the following C++ library:
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// https://github.com/rigtorp/MPMCQueue
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type MPMCQueueOf[I any] struct {
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cap uint64
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head uint64
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//lint:ignore U1000 prevents false sharing
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hpad [cacheLineSize - 8]byte
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tail uint64
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//lint:ignore U1000 prevents false sharing
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tpad [cacheLineSize - 8]byte
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slots []slotOfPadded[I]
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}
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type slotOfPadded[I any] struct {
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slotOf[I]
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// Unfortunately, proper padding like the below one:
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//
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// pad [cacheLineSize - (unsafe.Sizeof(slotOf[I]{}) % cacheLineSize)]byte
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//
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// won't compile, so here we add a best-effort padding for items up to
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// 56 bytes size.
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//lint:ignore U1000 prevents false sharing
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pad [cacheLineSize - unsafe.Sizeof(atomic.Uint64{})]byte
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}
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type slotOf[I any] struct {
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// atomic.Uint64 is used here to get proper 8 byte alignment on
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// 32-bit archs.
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turn atomic.Uint64
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item I
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}
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// NewMPMCQueueOf creates a new MPMCQueueOf instance with the given
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// capacity.
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func NewMPMCQueueOf[I any](capacity int) *MPMCQueueOf[I] {
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if capacity < 1 {
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panic("capacity must be positive number")
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}
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return &MPMCQueueOf[I]{
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cap: uint64(capacity),
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slots: make([]slotOfPadded[I], capacity),
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}
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}
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// Enqueue inserts the given item into the queue.
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// Blocks, if the queue is full.
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func (q *MPMCQueueOf[I]) Enqueue(item I) {
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head := atomic.AddUint64(&q.head, 1) - 1
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slot := &q.slots[q.idx(head)]
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turn := q.turn(head) * 2
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for slot.turn.Load() != turn {
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runtime.Gosched()
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}
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slot.item = item
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slot.turn.Store(turn + 1)
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}
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// Dequeue retrieves and removes the item from the head of the queue.
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// Blocks, if the queue is empty.
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func (q *MPMCQueueOf[I]) Dequeue() I {
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var zeroedI I
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tail := atomic.AddUint64(&q.tail, 1) - 1
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slot := &q.slots[q.idx(tail)]
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turn := q.turn(tail)*2 + 1
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for slot.turn.Load() != turn {
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runtime.Gosched()
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}
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item := slot.item
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slot.item = zeroedI
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slot.turn.Store(turn + 1)
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return item
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}
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// TryEnqueue inserts the given item into the queue. Does not block
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// and returns immediately. The result indicates that the queue isn't
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// full and the item was inserted.
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func (q *MPMCQueueOf[I]) TryEnqueue(item I) bool {
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head := atomic.LoadUint64(&q.head)
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for {
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slot := &q.slots[q.idx(head)]
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turn := q.turn(head) * 2
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if slot.turn.Load() == turn {
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if atomic.CompareAndSwapUint64(&q.head, head, head+1) {
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slot.item = item
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slot.turn.Store(turn + 1)
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return true
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}
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} else {
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prevHead := head
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head = atomic.LoadUint64(&q.head)
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if head == prevHead {
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return false
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}
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}
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runtime.Gosched()
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}
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}
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// TryDequeue retrieves and removes the item from the head of the
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// queue. Does not block and returns immediately. The ok result
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// indicates that the queue isn't empty and an item was retrieved.
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func (q *MPMCQueueOf[I]) TryDequeue() (item I, ok bool) {
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tail := atomic.LoadUint64(&q.tail)
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for {
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slot := &q.slots[q.idx(tail)]
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turn := q.turn(tail)*2 + 1
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if slot.turn.Load() == turn {
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if atomic.CompareAndSwapUint64(&q.tail, tail, tail+1) {
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var zeroedI I
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item = slot.item
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ok = true
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slot.item = zeroedI
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slot.turn.Store(turn + 1)
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return
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}
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} else {
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prevTail := tail
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tail = atomic.LoadUint64(&q.tail)
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if tail == prevTail {
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return
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}
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}
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runtime.Gosched()
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}
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}
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func (q *MPMCQueueOf[I]) idx(i uint64) uint64 {
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return i % q.cap
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}
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func (q *MPMCQueueOf[I]) turn(i uint64) uint64 {
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return i / q.cap
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}
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