1 files changed, 141 insertions, 0 deletions
diff --git a/internal/queue/simple.go b/internal/queue/simple.go
new file mode 100644
index 000000000..9307183f2
--- /dev/null
+++ b/internal/queue/simple.go
@@ -0,0 +1,141 @@
+// 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"
+)
+
+// 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 []*list.Elem[T]
+	w chan struct{}
+	m sync.Mutex
+}
+
+// Push will push given value to the queue.
+func (q *SimpleQueue[T]) Push(value T) {
+	q.m.Lock()
+	elem := q.alloc()
+	elem.Value = value
+	q.l.PushElemFront(elem)
+	if q.w != nil {
+		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()
+	if ok = (q.l.Tail != nil); ok {
+		tail := q.l.Tail
+		value = tail.Value
+		q.l.Remove(tail)
+		q.free(tail)
+	}
+	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.free(elem)
+
+	// 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
+}
+
+// alloc will allocate new list element (relying on memory pool).
+func (q *SimpleQueue[T]) alloc() *list.Elem[T] {
+	if len(q.p) > 0 {
+		elem := q.p[len(q.p)-1]
+		q.p = q.p[:len(q.p)-1]
+		return elem
+	}
+	return new(list.Elem[T])
+}
+
+// free will free list element and release to pool.
+func (q *SimpleQueue[T]) free(elem *list.Elem[T]) {
+	var zero T
+	elem.Next = nil
+	elem.Prev = nil
+	elem.Value = zero
+	q.p = append(q.p, elem)
+}