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 (
22 "errors"
23 "sync"
24)
25
26// Unbounded is an implementation of an unbounded buffer which does not use
27// extra goroutines. This is typically used for passing updates from one entity
28// to another within gRPC.
29//
30// All methods on this type are thread-safe and don't block on anything except
31// the underlying mutex used for synchronization.
32//
33// Unbounded supports values of any type to be stored in it by using a channel
34// of `any`. This means that a call to Put() incurs an extra memory allocation,
35// and also that users need a type assertion while reading. For performance
36// critical code paths, using Unbounded is strongly discouraged and defining a
37// new type specific implementation of this buffer is preferred. See
38// internal/transport/transport.go for an example of this.
39type Unbounded struct {
40 c chan any
41 closed bool
42 closing bool
43 mu sync.Mutex
44 backlog []any
45}
46
47// NewUnbounded returns a new instance of Unbounded.
48func NewUnbounded() *Unbounded {
49 return &Unbounded{c: make(chan any, 1)}
50}
51
52var errBufferClosed = errors.New("Put called on closed buffer.Unbounded")
53
54// Put adds t to the unbounded buffer.
55func (b *Unbounded) Put(t any) error {
56 b.mu.Lock()
57 defer b.mu.Unlock()
58 if b.closing {
59 return errBufferClosed
60 }
61 if len(b.backlog) == 0 {
62 select {
63 case b.c <- t:
64 return nil
65 default:
66 }
67 }
68 b.backlog = append(b.backlog, t)
69 return nil
70}
71
72// Load sends the earliest buffered data, if any, onto the read channel returned
73// by Get(). Users are expected to call this every time they successfully read a
74// value from the read channel.
75func (b *Unbounded) Load() {
76 b.mu.Lock()
77 defer b.mu.Unlock()
78 if len(b.backlog) > 0 {
79 select {
80 case b.c <- b.backlog[0]:
81 b.backlog[0] = nil
82 b.backlog = b.backlog[1:]
83 default:
84 }
85 } else if b.closing && !b.closed {
86 close(b.c)
87 }
88}
89
90// Get returns a read channel on which values added to the buffer, via Put(),
91// are sent on.
92//
93// Upon reading a value from this channel, users are expected to call Load() to
94// send the next buffered value onto the channel if there is any.
95//
96// If the unbounded buffer is closed, the read channel returned by this method
97// is closed after all data is drained.
98func (b *Unbounded) Get() <-chan any {
99 return b.c
100}
101
102// Close closes the unbounded buffer. No subsequent data may be Put(), and the
103// channel returned from Get() will be closed after all the data is read and
104// Load() is called for the final time.
105func (b *Unbounded) Close() {
106 b.mu.Lock()
107 defer b.mu.Unlock()
108 if b.closing {
109 return
110 }
111 b.closing = true
112 if len(b.backlog) == 0 {
113 b.closed = true
114 close(b.c)
115 }
116}