forked from Workiva/go-datastructures
-
Notifications
You must be signed in to change notification settings - Fork 0
/
queue.go
411 lines (342 loc) · 9.21 KB
/
queue.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
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
/*
Copyright 2014 Workiva, LLC
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 queue includes a regular queue and a priority queue.
These queues rely on waitgroups to pause listening threads
on empty queues until a message is received. If any thread
calls Dispose on the queue, any listeners are immediately returned
with an error. Any subsequent put to the queue will return an error
as opposed to panicking as with channels. Queues will grow with unbounded
behavior as opposed to channels which can be buffered but will pause
while a thread attempts to put to a full channel.
Recently added is a lockless ring buffer using the same basic C design as
found here:
http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue
Modified for use with Go with the addition of some dispose semantics providing
the capability to release blocked threads. This works for both puts
and gets, either will return an error if they are blocked and the buffer
is disposed. This could serve as a signal to kill a goroutine. All threadsafety
is acheived using CAS operations, making this buffer pretty quick.
Benchmarks:
BenchmarkPriorityQueue-8 2000000 782 ns/op
BenchmarkQueue-8 2000000 671 ns/op
BenchmarkChannel-8 1000000 2083 ns/op
BenchmarkQueuePut-8 20000 84299 ns/op
BenchmarkQueueGet-8 20000 80753 ns/op
BenchmarkExecuteInParallel-8 20000 68891 ns/op
BenchmarkRBLifeCycle-8 10000000 177 ns/op
BenchmarkRBPut-8 30000000 58.1 ns/op
BenchmarkRBGet-8 50000000 26.8 ns/op
TODO: We really need a Fibonacci heap for the priority queue.
TODO: Unify the types of queue to the same interface.
*/
package queue
import (
"runtime"
"sync"
"sync/atomic"
"time"
)
type waiters []*sema
func (w *waiters) get() *sema {
if len(*w) == 0 {
return nil
}
sema := (*w)[0]
copy((*w)[0:], (*w)[1:])
(*w)[len(*w)-1] = nil // or the zero value of T
*w = (*w)[:len(*w)-1]
return sema
}
func (w *waiters) put(sema *sema) {
*w = append(*w, sema)
}
func (w *waiters) remove(sema *sema) {
if len(*w) == 0 {
return
}
// build new slice, copy all except sema
ws := *w
newWs := make(waiters, 0, len(*w))
for i := range ws {
if ws[i] != sema {
newWs = append(newWs, ws[i])
}
}
*w = newWs
}
type items []interface{}
func (items *items) get(number int64) []interface{} {
returnItems := make([]interface{}, 0, number)
index := int64(0)
for i := int64(0); i < number; i++ {
if i >= int64(len(*items)) {
break
}
returnItems = append(returnItems, (*items)[i])
(*items)[i] = nil
index++
}
*items = (*items)[index:]
return returnItems
}
func (items *items) peek() (interface{}, bool) {
length := len(*items)
if length == 0 {
return nil, false
}
return (*items)[0], true
}
func (items *items) getUntil(checker func(item interface{}) bool) []interface{} {
length := len(*items)
if len(*items) == 0 {
// returning nil here actually wraps that nil in a list
// of interfaces... thanks go
return []interface{}{}
}
returnItems := make([]interface{}, 0, length)
index := -1
for i, item := range *items {
if !checker(item) {
break
}
returnItems = append(returnItems, item)
index = i
(*items)[i] = nil // prevent memory leak
}
*items = (*items)[index+1:]
return returnItems
}
type sema struct {
ready chan bool
response *sync.WaitGroup
}
func newSema() *sema {
return &sema{
ready: make(chan bool, 1),
response: &sync.WaitGroup{},
}
}
// Queue is the struct responsible for tracking the state
// of the queue.
type Queue struct {
waiters waiters
items items
lock sync.Mutex
disposed bool
}
// Put will add the specified items to the queue.
func (q *Queue) Put(items ...interface{}) error {
if len(items) == 0 {
return nil
}
q.lock.Lock()
if q.disposed {
q.lock.Unlock()
return ErrDisposed
}
q.items = append(q.items, items...)
for {
sema := q.waiters.get()
if sema == nil {
break
}
sema.response.Add(1)
select {
case sema.ready <- true:
sema.response.Wait()
default:
// This semaphore timed out.
}
if len(q.items) == 0 {
break
}
}
q.lock.Unlock()
return nil
}
// Get retrieves items from the queue. If there are some items in the
// queue, get will return a number UP TO the number passed in as a
// parameter. If no items are in the queue, this method will pause
// until items are added to the queue.
func (q *Queue) Get(number int64) ([]interface{}, error) {
return q.Poll(number, 0)
}
// Poll retrieves items from the queue. If there are some items in the queue,
// Poll will return a number UP TO the number passed in as a parameter. If no
// items are in the queue, this method will pause until items are added to the
// queue or the provided timeout is reached. A non-positive timeout will block
// until items are added. If a timeout occurs, ErrTimeout is returned.
func (q *Queue) Poll(number int64, timeout time.Duration) ([]interface{}, error) {
if number < 1 {
// thanks again go
return []interface{}{}, nil
}
q.lock.Lock()
if q.disposed {
q.lock.Unlock()
return nil, ErrDisposed
}
var items []interface{}
if len(q.items) == 0 {
sema := newSema()
q.waiters.put(sema)
q.lock.Unlock()
var timeoutC <-chan time.Time
if timeout > 0 {
timeoutC = time.After(timeout)
}
select {
case <-sema.ready:
// we are now inside the put's lock
if q.disposed {
return nil, ErrDisposed
}
items = q.items.get(number)
sema.response.Done()
return items, nil
case <-timeoutC:
// cleanup the sema that was added to waiters
select {
case sema.ready <- true:
// we called this before Put() could
// Remove sema from waiters.
q.lock.Lock()
q.waiters.remove(sema)
q.lock.Unlock()
default:
// Put() got it already, we need to call Done() so Put() can move on
sema.response.Done()
}
return nil, ErrTimeout
}
}
items = q.items.get(number)
q.lock.Unlock()
return items, nil
}
// Peek returns a the first item in the queue by value
// without modifying the queue.
func (q *Queue) Peek() (interface{}, error) {
q.lock.Lock()
defer q.lock.Unlock()
if q.disposed {
return nil, ErrDisposed
}
peekItem, ok := q.items.peek()
if !ok {
return nil, ErrEmptyQueue
}
return peekItem, nil
}
// TakeUntil takes a function and returns a list of items that
// match the checker until the checker returns false. This does not
// wait if there are no items in the queue.
func (q *Queue) TakeUntil(checker func(item interface{}) bool) ([]interface{}, error) {
if checker == nil {
return nil, nil
}
q.lock.Lock()
if q.disposed {
q.lock.Unlock()
return nil, ErrDisposed
}
result := q.items.getUntil(checker)
q.lock.Unlock()
return result, nil
}
// Empty returns a bool indicating if this bool is empty.
func (q *Queue) Empty() bool {
q.lock.Lock()
defer q.lock.Unlock()
return len(q.items) == 0
}
// Len returns the number of items in this queue.
func (q *Queue) Len() int64 {
q.lock.Lock()
defer q.lock.Unlock()
return int64(len(q.items))
}
// Disposed returns a bool indicating if this queue
// has had disposed called on it.
func (q *Queue) Disposed() bool {
q.lock.Lock()
defer q.lock.Unlock()
return q.disposed
}
// Dispose will dispose of this queue and returns
// the items disposed. Any subsequent calls to Get
// or Put will return an error.
func (q *Queue) Dispose() []interface{} {
q.lock.Lock()
defer q.lock.Unlock()
q.disposed = true
for _, waiter := range q.waiters {
waiter.response.Add(1)
select {
case waiter.ready <- true:
// release Poll immediately
default:
// ignore if it's a timeout or in the get
}
}
disposedItems := q.items
q.items = nil
q.waiters = nil
return disposedItems
}
// New is a constructor for a new threadsafe queue.
func New(hint int64) *Queue {
return &Queue{
items: make([]interface{}, 0, hint),
}
}
// ExecuteInParallel will (in parallel) call the provided function
// with each item in the queue until the queue is exhausted. When the queue
// is exhausted execution is complete and all goroutines will be killed.
// This means that the queue will be disposed so cannot be used again.
func ExecuteInParallel(q *Queue, fn func(interface{})) {
if q == nil {
return
}
q.lock.Lock() // so no one touches anything in the middle
// of this process
todo, done := uint64(len(q.items)), int64(-1)
// this is important or we might face an infinite loop
if todo == 0 {
return
}
numCPU := 1
if runtime.NumCPU() > 1 {
numCPU = runtime.NumCPU() - 1
}
var wg sync.WaitGroup
wg.Add(numCPU)
items := q.items
for i := 0; i < numCPU; i++ {
go func() {
for {
index := atomic.AddInt64(&done, 1)
if index >= int64(todo) {
wg.Done()
break
}
fn(items[index])
items[index] = 0
}
}()
}
wg.Wait()
q.lock.Unlock()
q.Dispose()
}