1/*
2 * Copyright 2019 gRPC authors.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *     http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 *
16 */
17
18// Package buffer provides an implementation of an unbounded buffer.
19package buffer
20
21import "sync"
22
23// Unbounded is an implementation of an unbounded buffer which does not use
24// extra goroutines. This is typically used for passing updates from one entity
25// to another within gRPC.
26//
27// All methods on this type are thread-safe and don't block on anything except
28// the underlying mutex used for synchronization.
29type Unbounded struct {
30	c       chan interface{}
31	mu      sync.Mutex
32	backlog []interface{}
33}
34
35// NewUnbounded returns a new instance of Unbounded.
36func NewUnbounded() *Unbounded {
37	return &Unbounded{c: make(chan interface{}, 1)}
38}
39
40// Put adds t to the unbounded buffer.
41func (b *Unbounded) Put(t interface{}) {
42	b.mu.Lock()
43	if len(b.backlog) == 0 {
44		select {
45		case b.c <- t:
46			b.mu.Unlock()
47			return
48		default:
49		}
50	}
51	b.backlog = append(b.backlog, t)
52	b.mu.Unlock()
53}
54
55// Load sends the earliest buffered data, if any, onto the read channel
56// returned by Get(). Users are expected to call this every time they read a
57// value from the read channel.
58func (b *Unbounded) Load() {
59	b.mu.Lock()
60	if len(b.backlog) > 0 {
61		select {
62		case b.c <- b.backlog[0]:
63			b.backlog[0] = nil
64			b.backlog = b.backlog[1:]
65		default:
66		}
67	}
68	b.mu.Unlock()
69}
70
71// Get returns a read channel on which values added to the buffer, via Put(),
72// are sent on.
73//
74// Upon reading a value from this channel, users are expected to call Load() to
75// send the next buffered value onto the channel if there is any.
76func (b *Unbounded) Get() <-chan interface{} {
77	return b.c
78}
79