cubefs

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.
19
package buffer
20

21
import "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.
36
type Unbounded struct {
37
	c       chan interface{}
38
	mu      sync.Mutex
39
	backlog []interface{}
40
}
41

42
// NewUnbounded returns a new instance of Unbounded.
43
func NewUnbounded() *Unbounded {
44
	return &Unbounded{c: make(chan interface{}, 1)}
45
}
46

47
// Put adds t to the unbounded buffer.
48
func (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.
65
func (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.
83
func (b *Unbounded) Get() <-chan interface{} {
84
	return b.c
85
}
86