-
Notifications
You must be signed in to change notification settings - Fork 19
/
fan_out_event_source.go
114 lines (94 loc) · 2.87 KB
/
fan_out_event_source.go
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
// Copyright (c) 2022 Gobalsky Labs Limited
//
// Use of this software is governed by the Business Source License included
// in the LICENSE.DATANODE file and at https://www.mariadb.com/bsl11.
//
// Change Date: 18 months from the later of the date of the first publicly
// available Distribution of this version of the repository, and 25 June 2022.
//
// On the date above, in accordance with the Business Source License, use
// of this software will be governed by version 3 or later of the GNU General
// Public License.
package broker
import (
"context"
"sync"
"code.vegaprotocol.io/vega/core/events"
)
// fanOutEventSource: an event source to fan out an event stream, it is told in advance the number of subscribers to
// expect and only starts publishing events once that number of subscriptions has been received.
type fanOutEventSource struct {
source eventSource
sendChannelBufferSize int
expectedNumSubscribers int
numSubscribers int
eventChannels []chan events.Event
errorChannels []chan error
listening bool
mutex sync.Mutex
}
func NewFanOutEventSource(source eventSource, sendChannelBufferSize int, expectedNumSubscribers int) *fanOutEventSource {
return &fanOutEventSource{
source: source,
sendChannelBufferSize: sendChannelBufferSize,
expectedNumSubscribers: expectedNumSubscribers,
}
}
func (e *fanOutEventSource) Listen() error {
e.mutex.Lock()
defer e.mutex.Unlock()
if !e.listening {
err := e.source.Listen()
if err != nil {
return err
}
e.listening = true
}
return nil
}
func (e *fanOutEventSource) Receive(ctx context.Context) (<-chan events.Event, <-chan error) {
e.mutex.Lock()
defer e.mutex.Unlock()
eventsCh := make(chan events.Event, e.sendChannelBufferSize)
errorCh := make(chan error, 1)
e.eventChannels = append(e.eventChannels, eventsCh)
e.errorChannels = append(e.errorChannels, errorCh)
e.numSubscribers++
if e.numSubscribers > e.expectedNumSubscribers {
panic("number of subscribers exceeded expected subscriber number")
}
// Once the number of subscribers equals the expected number start forwarding events
if e.numSubscribers == e.expectedNumSubscribers {
go e.sendEvents(ctx)
}
return eventsCh, errorCh
}
func (e *fanOutEventSource) sendEvents(ctx context.Context) {
srcEventCh, srcErrorCh := e.source.Receive(ctx)
defer func() {
for _, evtCh := range e.eventChannels {
close(evtCh)
}
for _, errorCh := range e.errorChannels {
close(errorCh)
}
}()
for event := range srcEventCh {
for _, evtCh := range e.eventChannels {
// Listen for context cancels, even if we're blocked sending events
select {
case evtCh <- event:
case <-ctx.Done():
return
}
}
}
select {
case err := <-srcErrorCh:
for _, errorCh := range e.errorChannels {
errorCh <- err
}
default:
// Do nothing, continue
}
}