vitess.io/vitess@v0.16.2/go/sync2/batcher.go (about)

     1  /*
     2  Copyright 2019 The Vitess 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  package sync2
    18  
    19  import (
    20  	"time"
    21  )
    22  
    23  // Batcher delays concurrent operations for a configurable interval in order to
    24  // batch them up or otherwise clock their operation to run concurrently.
    25  //
    26  // It is implemented as a channel of int32s. Each waiter blocks on the channel
    27  // from which it gets a sequentially increasing batch ID when the timer elapses.
    28  //
    29  // Hence a waiter is delayed for at most the batch interval.
    30  type Batcher struct {
    31  	interval time.Duration
    32  	queue    chan int
    33  	waiters  AtomicInt32
    34  	nextID   AtomicInt32
    35  	after    func(time.Duration) <-chan time.Time
    36  }
    37  
    38  // NewBatcher returns a new Batcher
    39  func NewBatcher(interval time.Duration) *Batcher {
    40  	return &Batcher{
    41  		interval: interval,
    42  		queue:    make(chan int),
    43  		waiters:  NewAtomicInt32(0),
    44  		nextID:   NewAtomicInt32(0),
    45  		after:    time.After,
    46  	}
    47  }
    48  
    49  // newBatcherForTest returns a Batcher for testing where time.After can
    50  // be replaced by a fake alternative.
    51  func newBatcherForTest(interval time.Duration, after func(time.Duration) <-chan time.Time) *Batcher {
    52  	return &Batcher{
    53  		interval: interval,
    54  		queue:    make(chan int),
    55  		waiters:  NewAtomicInt32(0),
    56  		nextID:   NewAtomicInt32(0),
    57  		after:    after,
    58  	}
    59  }
    60  
    61  // Wait adds a new waiter to the queue and blocks until the next batch
    62  func (b *Batcher) Wait() int {
    63  	numWaiters := b.waiters.Add(1)
    64  	if numWaiters == 1 {
    65  		b.newBatch()
    66  	}
    67  	return <-b.queue
    68  }
    69  
    70  // newBatch starts a new batch
    71  func (b *Batcher) newBatch() {
    72  	go func() {
    73  		<-b.after(b.interval)
    74  
    75  		id := b.nextID.Add(1)
    76  
    77  		// Make sure to atomically reset the number of waiters to make
    78  		// sure that all incoming requests either make it into the
    79  		// current batch or the next one.
    80  		waiters := b.waiters.Get()
    81  		for !b.waiters.CompareAndSwap(waiters, 0) {
    82  			waiters = b.waiters.Get()
    83  		}
    84  
    85  		for i := int32(0); i < waiters; i++ {
    86  			b.queue <- int(id)
    87  		}
    88  	}()
    89  }