chainntnfs: Implement unbounded concurrent-safe FIFO queue.

This can be used in at least one place in the notifiers to improve
efficiency and reduce complexity.
This commit is contained in:
Jim Posen 2017-09-29 12:09:37 -07:00 committed by Olaoluwa Osuntokun
parent 555cead5ad
commit 726c8b2301
2 changed files with 112 additions and 0 deletions

86
chainntnfs/queue.go Normal file

@ -0,0 +1,86 @@
package chainntnfs
import (
"container/list"
)
// ConcurrentQueue is a concurrent-safe FIFO queue with unbounded capacity.
// Clients interact with the queue by pushing items into the in channel and
// popping items from the out channel. There is a goroutine that manages moving
// items from the in channel to the out channel in the correct order that must
// be started by calling Start().
type ConcurrentQueue struct {
chanIn chan interface{}
chanOut chan interface{}
quit chan struct{}
overflow *list.List
}
// NewConcurrentQueue constructs a ConcurrentQueue. The bufferSize parameter is
// the capacity of the output channel. When the size of the queue is below this
// threshold, pushes do not incur the overhead of the less efficient overflow
// structure.
func NewConcurrentQueue(bufferSize int) *ConcurrentQueue {
return &ConcurrentQueue{
chanIn: make(chan interface{}),
chanOut: make(chan interface{}, bufferSize),
quit: make(chan struct{}),
overflow: list.New(),
}
}
// ChanIn returns a channel that can be used to push new items into the queue.
func (cq *ConcurrentQueue) ChanIn() chan<- interface{} {
return cq.chanIn
}
// ChanOut returns a channel that can be used to pop items from the queue.
func (cq *ConcurrentQueue) ChanOut() <-chan interface{} {
return cq.chanOut
}
// Start begins a goroutine that manages moving items from the in channel to the
// out channel. The queue tries to move items directly to the out channel
// minimize overhead, but if the out channel is full it pushes items to an
// overflow queue. This must be called before using the queue.
func (cq *ConcurrentQueue) Start() {
go func() {
for {
nextElement := cq.overflow.Front()
if nextElement == nil {
// Overflow queue is empty so incoming items can be pushed
// directly to the output channel. If output channel is full
// though, push to overflow.
select {
case item := <-cq.chanIn:
select {
case cq.chanOut <- item:
// Optimistically push directly to chanOut
default:
cq.overflow.PushBack(item)
}
case <-cq.quit:
return
}
} else {
// Overflow queue is not empty, so any new items get pushed to
// the back to preserve order.
select {
case item := <-cq.chanIn:
cq.overflow.PushBack(item)
case cq.chanOut <- nextElement.Value:
cq.overflow.Remove(nextElement)
case <-cq.quit:
return
}
}
}
}()
}
// Stop ends the goroutine that moves items from the in channel to the out
// channel. This does not clear the queue state, so the queue can be restarted
// without dropping items.
func (cq *ConcurrentQueue) Stop() {
cq.quit <- struct{}{}
}

26
chainntnfs/queue_test.go Normal file

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package chainntnfs_test
import (
"testing"
"github.com/lightningnetwork/lnd/chainntnfs"
)
func TestConcurrentQueue(t *testing.T) {
queue := chainntnfs.NewConcurrentQueue(100)
queue.Start()
defer queue.Stop()
// Pushes should never block for long.
for i := 0; i < 1000; i++ {
queue.ChanIn() <- i
}
// Pops also should not block for long. Expect elements in FIFO order.
for i := 0; i < 1000; i++ {
item := <-queue.ChanOut()
if i != item.(int) {
t.Fatalf("Dequeued wrong value: expected %d, got %d", i, item.(int))
}
}
}