126 lines
3.3 KiB
Go
126 lines
3.3 KiB
Go
package queue
|
|
|
|
import (
|
|
"container/list"
|
|
"sync"
|
|
)
|
|
|
|
// 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 {
|
|
started sync.Once
|
|
stopped sync.Once
|
|
|
|
chanIn chan interface{}
|
|
chanOut chan interface{}
|
|
overflow *list.List
|
|
|
|
wg sync.WaitGroup
|
|
quit chan struct{}
|
|
}
|
|
|
|
// 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),
|
|
overflow: list.New(),
|
|
quit: make(chan struct{}),
|
|
}
|
|
}
|
|
|
|
// 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() {
|
|
cq.started.Do(cq.start)
|
|
}
|
|
|
|
func (cq *ConcurrentQueue) start() {
|
|
cq.wg.Add(1)
|
|
go func() {
|
|
defer cq.wg.Done()
|
|
|
|
readLoop:
|
|
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, ok := <-cq.chanIn:
|
|
if !ok {
|
|
break readLoop
|
|
}
|
|
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, ok := <-cq.chanIn:
|
|
if !ok {
|
|
break readLoop
|
|
}
|
|
cq.overflow.PushBack(item)
|
|
case cq.chanOut <- nextElement.Value:
|
|
cq.overflow.Remove(nextElement)
|
|
case <-cq.quit:
|
|
return
|
|
}
|
|
}
|
|
}
|
|
|
|
// Incoming channel has been closed. Empty overflow queue into
|
|
// the outgoing channel.
|
|
nextElement := cq.overflow.Front()
|
|
for nextElement != nil {
|
|
select {
|
|
case cq.chanOut <- nextElement.Value:
|
|
cq.overflow.Remove(nextElement)
|
|
case <-cq.quit:
|
|
return
|
|
}
|
|
nextElement = cq.overflow.Front()
|
|
}
|
|
|
|
// Close outgoing channel.
|
|
close(cq.chanOut)
|
|
}()
|
|
}
|
|
|
|
// 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.stopped.Do(func() {
|
|
close(cq.quit)
|
|
cq.wg.Wait()
|
|
})
|
|
}
|