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// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package queue
import (
"context"
"sync"
"codeberg.org/gruf/go-list"
)
// frequency of GC cycles
// per no. unlocks. i.e.
// every 'gcfreq' unlocks.
const gcfreq = 1024
// SimpleQueue provides a simple concurrency safe
// queue using generics and a memory pool of list
// elements to reduce overall memory usage.
type SimpleQueue[T any] struct {
l list.List[T]
p elemPool[T]
w chan struct{}
m sync.Mutex
n uint32 // pop counter (safely wraps around)
}
// Push will push given value to the queue.
func (q *SimpleQueue[T]) Push(value T) {
q.m.Lock()
// Wrap in element.
elem := q.p.alloc()
elem.Value = value
// Push new elem to queue.
q.l.PushElemFront(elem)
if q.w != nil {
// Notify any goroutines
// blocking on q.Wait(),
// or on PopCtx(...).
close(q.w)
q.w = nil
}
q.m.Unlock()
}
// Pop will attempt to pop value from the queue.
func (q *SimpleQueue[T]) Pop() (value T, ok bool) {
q.m.Lock()
// Check for a tail (i.e. not empty).
if ok = (q.l.Tail != nil); ok {
// Extract value.
tail := q.l.Tail
value = tail.Value
// Remove tail.
q.l.Remove(tail)
q.p.free(tail)
// Every 'gcfreq' pops perform
// a garbage collection to keep
// us squeaky clean :]
if q.n++; q.n%gcfreq == 0 {
q.p.GC()
}
}
q.m.Unlock()
return
}
// PopCtx will attempt to pop value from queue, else blocking on context.
func (q *SimpleQueue[T]) PopCtx(ctx context.Context) (value T, ok bool) {
// Acquire lock.
q.m.Lock()
var elem *list.Elem[T]
for {
// Get next elem.
elem = q.l.Tail
if ok = (elem != nil); ok {
break
}
if q.w == nil {
// Create new wait channel.
q.w = make(chan struct{})
}
// Get current
// ch pointer.
ch := q.w
// Done with lock.
q.m.Unlock()
select {
// Context canceled.
case <-ctx.Done():
return
// Pushed!
case <-ch:
}
// Relock queue.
q.m.Lock()
}
// Extract value.
value = elem.Value
// Remove element.
q.l.Remove(elem)
q.p.free(elem)
// Every 'gcfreq' pops perform
// a garbage collection to keep
// us squeaky clean :]
if q.n++; q.n%gcfreq == 0 {
q.p.GC()
}
// Done with lock.
q.m.Unlock()
return
}
// Len returns the current length of the queue.
func (q *SimpleQueue[T]) Len() int {
q.m.Lock()
l := q.l.Len()
q.m.Unlock()
return l
}
// elemPool is a very simple
// list.Elem[T] memory pool.
type elemPool[T any] struct {
current []*list.Elem[T]
victim []*list.Elem[T]
}
func (p *elemPool[T]) alloc() *list.Elem[T] {
// First try the current queue
if l := len(p.current) - 1; l >= 0 {
mu := p.current[l]
p.current = p.current[:l]
return mu
}
// Next try the victim queue.
if l := len(p.victim) - 1; l >= 0 {
mu := p.victim[l]
p.victim = p.victim[:l]
return mu
}
// Lastly, alloc new.
mu := new(list.Elem[T])
return mu
}
// free will release given element to pool.
func (p *elemPool[T]) free(elem *list.Elem[T]) {
var zero T
elem.Next = nil
elem.Prev = nil
elem.Value = zero
p.current = append(p.current, elem)
}
// GC will clear out unused entries from the elemPool.
func (p *elemPool[T]) GC() {
current := p.current
p.current = nil
p.victim = current
}
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