1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
|
/*
*
* Copyright 2022 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package grpcsync
import (
"context"
"sync"
"google.golang.org/grpc/internal/buffer"
)
// CallbackSerializer provides a mechanism to schedule callbacks in a
// synchronized manner. It provides a FIFO guarantee on the order of execution
// of scheduled callbacks. New callbacks can be scheduled by invoking the
// Schedule() method.
//
// This type is safe for concurrent access.
type CallbackSerializer struct {
// Done is closed once the serializer is shut down completely, i.e all
// scheduled callbacks are executed and the serializer has deallocated all
// its resources.
Done chan struct{}
callbacks *buffer.Unbounded
closedMu sync.Mutex
closed bool
}
// NewCallbackSerializer returns a new CallbackSerializer instance. The provided
// context will be passed to the scheduled callbacks. Users should cancel the
// provided context to shutdown the CallbackSerializer. It is guaranteed that no
// callbacks will be added once this context is canceled, and any pending un-run
// callbacks will be executed before the serializer is shut down.
func NewCallbackSerializer(ctx context.Context) *CallbackSerializer {
t := &CallbackSerializer{
Done: make(chan struct{}),
callbacks: buffer.NewUnbounded(),
}
go t.run(ctx)
return t
}
// Schedule adds a callback to be scheduled after existing callbacks are run.
//
// Callbacks are expected to honor the context when performing any blocking
// operations, and should return early when the context is canceled.
//
// Return value indicates if the callback was successfully added to the list of
// callbacks to be executed by the serializer. It is not possible to add
// callbacks once the context passed to NewCallbackSerializer is cancelled.
func (t *CallbackSerializer) Schedule(f func(ctx context.Context)) bool {
t.closedMu.Lock()
defer t.closedMu.Unlock()
if t.closed {
return false
}
t.callbacks.Put(f)
return true
}
func (t *CallbackSerializer) run(ctx context.Context) {
var backlog []func(context.Context)
defer close(t.Done)
for ctx.Err() == nil {
select {
case <-ctx.Done():
// Do nothing here. Next iteration of the for loop will not happen,
// since ctx.Err() would be non-nil.
case callback, ok := <-t.callbacks.Get():
if !ok {
return
}
t.callbacks.Load()
callback.(func(ctx context.Context))(ctx)
}
}
// Fetch pending callbacks if any, and execute them before returning from
// this method and closing t.Done.
t.closedMu.Lock()
t.closed = true
backlog = t.fetchPendingCallbacks()
t.callbacks.Close()
t.closedMu.Unlock()
for _, b := range backlog {
b(ctx)
}
}
func (t *CallbackSerializer) fetchPendingCallbacks() []func(context.Context) {
var backlog []func(context.Context)
for {
select {
case b := <-t.callbacks.Get():
backlog = append(backlog, b.(func(context.Context)))
t.callbacks.Load()
default:
return backlog
}
}
}
|
