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// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build go1.21
package quic
import "context"
// A queue is an unbounded queue of some item (new connections and streams).
type queue[T any] struct {
// The gate condition is set if the queue is non-empty or closed.
gate gate
err error
q []T
func newQueue[T any]() queue[T] {
return queue[T]{gate: newGate()}
// close closes the queue, causing pending and future pop operations
// to return immediately with err.
func (q *queue[T]) close(err error) {
defer q.unlock()
if q.err == nil {
q.err = err
// put appends an item to the queue.
// It returns true if the item was added, false if the queue is closed.
func (q *queue[T]) put(v T) bool {
defer q.unlock()
if q.err != nil {
return false
q.q = append(q.q, v)
return true
// get removes the first item from the queue, blocking until ctx is done, an item is available,
// or the queue is closed.
func (q *queue[T]) get(ctx context.Context) (T, error) {
return q.getWithHooks(ctx, nil)
// getWithHooks is get, but uses testHooks for locking when non-nil.
// This is a bit of an layer violation, but a simplification overall.
func (q *queue[T]) getWithHooks(ctx context.Context, testHooks connTestHooks) (T, error) {
var zero T
var err error
if testHooks != nil {
err = testHooks.waitAndLockGate(ctx, &q.gate)
} else {
err = q.gate.waitAndLockContext(ctx)
if err != nil {
return zero, err
defer q.unlock()
if q.err != nil {
return zero, q.err
v := q.q[0]
copy(q.q[:], q.q[1:])
q.q[len(q.q)-1] = zero
q.q = q.q[:len(q.q)-1]
return v, nil
func (q *queue[T]) unlock() {
q.gate.unlock(q.err != nil || len(q.q) > 0)