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.
29//
30// Unbounded supports values of any type to be stored in it by using a channel
31// of `interface{}`. This means that a call to Put() incurs an extra memory
32// allocation, and also that users need a type assertion while reading. For
33// performance critical code paths, using Unbounded is strongly discouraged and
34// defining a new type specific implementation of this buffer is preferred. See
35// internal/transport/transport.go for an example of this.
36type Unbounded struct {
37	c       chan interface{}
38	mu      sync.Mutex
39	backlog []interface{}
40}
41
42// NewUnbounded returns a new instance of Unbounded.
43func NewUnbounded() *Unbounded {
44	return &Unbounded{c: make(chan interface{}, 1)}
45}
46
47// Put adds t to the unbounded buffer.
48func (b *Unbounded) Put(t interface{}) {
49	b.mu.Lock()
50	if len(b.backlog) == 0 {
51		select {
52		case b.c <- t:
53			b.mu.Unlock()
54			return
55		default:
56		}
57	}
58	b.backlog = append(b.backlog, t)
59	b.mu.Unlock()
60}
61
62// Load sends the earliest buffered data, if any, onto the read channel
63// returned by Get(). Users are expected to call this every time they read a
64// value from the read channel.
65func (b *Unbounded) Load() {
66	b.mu.Lock()
67	if len(b.backlog) > 0 {
68		select {
69		case b.c <- b.backlog[0]:
70			b.backlog[0] = nil
71			b.backlog = b.backlog[1:]
72		default:
73		}
74	}
75	b.mu.Unlock()
76}
77
78// Get returns a read channel on which values added to the buffer, via Put(),
79// are sent on.
80//
81// Upon reading a value from this channel, users are expected to call Load() to
82// send the next buffered value onto the channel if there is any.
83func (b *Unbounded) Get() <-chan interface{} {
84	return b.c
85}
86