forked from scionproto/scion
-
Notifications
You must be signed in to change notification settings - Fork 0
/
ringbuf.go
184 lines (172 loc) · 5.1 KB
/
ringbuf.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
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
// Copyright 2017 ETH Zurich
//
// 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 ringbuf
import (
"sync"
"github.com/scionproto/scion/go/lib/ringbuf/internal/metrics"
)
type Entry interface{}
type EntryList []Entry
type NewEntryF func() interface{}
// Ring is a classic generic ring buffer on top of a fixed-sized slice. It is thread-safe.
type Ring struct {
mutex sync.Mutex
writableC *sync.Cond
readableC *sync.Cond
entries EntryList
writeIndex int
readIndex int
writable int
readable int
closed bool
metrics metrics.Ringbuf
}
// New allocates a new Ring instance, with capacity for count entries. If newf
// is non-nil, it is called count times to pre-allocate the entries.
// Metrics are exported with a 'ring_id" label.
func New(count int, newf NewEntryF, ringID string) *Ring {
r := &Ring{}
r.writableC = sync.NewCond(&r.mutex)
r.readableC = sync.NewCond(&r.mutex)
r.entries = make(EntryList, count)
// Only allocate memory if caller requested it
if newf != nil {
for i := 0; i < count; i++ {
r.entries[i] = newf()
}
// A ring buffer that allocates data starts off as full
r.readable = count
} else {
// A ring buffer that does not allocate starts off as empty
r.writable = count
}
r.closed = false
r.metrics = metrics.NewRingbuf(&metrics.RingbufLabels{RingID: ringID})
r.metrics.MaxEntries.Set(float64(count))
r.metrics.UsedEntries.Set(float64(r.readable))
return r
}
// Write copies entries to the internal ring buffer. If block is true, then
// Write will block until it is able to write at least one entry (or the Ring
// is closed). Otherwise it will return immediately if there's on space left
// for writing.
// In case entries is of length zero, the call returns immediately.
// Returns the number of entries written, or -1 if the RingBuf is closed, and a
// bool indicating if the write blocked.
func (r *Ring) Write(entries EntryList, block bool) (int, bool) {
r.mutex.Lock()
defer r.mutex.Unlock()
var blocked bool
r.metrics.WriteCalls.Inc()
if len(entries) > 0 && r.writable == 0 && !r.closed {
if !block {
return 0, blocked
}
r.metrics.WritesBlocked.Inc()
for r.writable == 0 && !r.closed {
blocked = true
r.writableC.Wait()
}
}
if r.closed {
return -1, blocked
}
n := min(r.writable, len(entries))
r.write(entries[:n])
r.writable -= n
r.readable += n
r.readableC.Broadcast()
r.metrics.WriteEntries.Observe(float64(n))
r.metrics.UsedEntries.Set(float64(r.readable))
return n, blocked
}
// Read copies entries from the internal ring buffer. If block is true, then
// Read will block until it is able to read at least one entry (or the Ring
// is closed). Otherwise it will return immediately if there's no entries
// available for reading.
// In case entries is of length zero, the call returns immediately.
// Returns the number of entries read, or -1 if the RingBuf is closed, and a
// bool indicating if the read blocked.
func (r *Ring) Read(entries EntryList, block bool) (int, bool) {
r.mutex.Lock()
defer r.mutex.Unlock()
var blocked bool
r.metrics.ReadCalls.Inc()
if len(entries) > 0 && r.readable == 0 && !r.closed {
if !block {
return 0, blocked
}
r.metrics.ReadsBlocked.Inc()
for r.readable == 0 && !r.closed {
blocked = true
r.readableC.Wait()
}
}
if r.closed && r.readable == 0 {
// Don't return -1 so long as there are still readable entries
// available.
return -1, blocked
}
n := min(r.readable, len(entries))
r.read(entries[:n])
r.readable -= n
r.writable += n
r.writableC.Broadcast()
r.metrics.ReadEntries.Observe(float64(n))
r.metrics.UsedEntries.Set(float64(r.readable))
return n, blocked
}
// Close closes the ring buffer, and causes all blocked readers/writers to be
// notified.
func (r *Ring) Close() {
r.mutex.Lock()
defer r.mutex.Unlock()
r.closed = true
r.writableC.Broadcast()
r.readableC.Broadcast()
}
func (r *Ring) write(entries EntryList) {
n := copy(r.entries[r.writeIndex:], entries)
r.writeIndex += n
// Wraparound if we need to write more slice references
if n < len(entries) {
n = copy(r.entries, entries[n:])
// Reset write index
r.writeIndex = n
}
}
func (r *Ring) read(entries EntryList) {
n := copy(entries, r.entries[r.readIndex:])
// Remove references that were just read.
for i := r.readIndex; i < r.readIndex+n; i++ {
r.entries[i] = nil
}
r.readIndex += n
// Wraparound if we need to read more slice references
if n < len(entries) {
n = copy(entries[n:], r.entries)
// Remove references that were just read.
for i := 0; i < n; i++ {
r.entries[i] = nil
}
// Reset read index
r.readIndex = n
}
}
func min(x, y int) int {
if x < y {
return x
}
return y
}