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// Copyright 2015 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.
// Package event provides an infinitely buffered double-ended queue of events.
package event // import "golang.org/x/exp/shiny/driver/internal/event"
import (
"sync"
)
// Deque is an infinitely buffered double-ended queue of events. The zero value
// is usable, but a Deque value must not be copied.
type Deque struct {
mu sync.Mutex
cond sync.Cond // cond.L is lazily initialized to &Deque.mu.
back []interface{} // FIFO.
front []interface{} // LIFO.
}
func (q *Deque) lockAndInit() {
q.mu.Lock()
if q.cond.L == nil {
q.cond.L = &q.mu
}
}
// NextEvent implements the screen.EventDeque interface.
func (q *Deque) NextEvent() interface{} {
q.lockAndInit()
defer q.mu.Unlock()
for {
if n := len(q.front); n > 0 {
e := q.front[n-1]
q.front[n-1] = nil
q.front = q.front[:n-1]
return e
}
if n := len(q.back); n > 0 {
e := q.back[0]
q.back[0] = nil
q.back = q.back[1:]
return e
}
q.cond.Wait()
}
}
// Send implements the screen.EventDeque interface.
func (q *Deque) Send(event interface{}) {
q.lockAndInit()
defer q.mu.Unlock()
q.back = append(q.back, event)
q.cond.Signal()
}
// SendFirst implements the screen.EventDeque interface.
func (q *Deque) SendFirst(event interface{}) {
q.lockAndInit()
defer q.mu.Unlock()
q.front = append(q.front, event)
q.cond.Signal()
}
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