I am trying to implement a priority queue to send json objects through a network socket based on priority. I am using the container/heap package to implement the queue. I came up with something like this:
for {
if pq.Len() > 0 {
item := heap.Pop(&pq).(*Item)
jsonEncoder.Encode(&item)
} else {
time.Sleep(10 * time.Millisecond)
}
}
Are there better ways to wait for a new item than just polling the priority queue?
分享 I'd probably use a couple a queuing goroutine. Starting with the data structures in the PriorityQueue example, I'd build a function like this:
http://play.golang.org/p/hcNFX8ehBW
func queue(in <-chan *Item, out chan<- *Item) {
// Make us a queue!
pq := make(PriorityQueue, 0)
heap.Init(&pq)
var currentItem *Item // Our item "in hand"
var currentIn = in // Current input channel (may be nil sometimes)
var currentOut chan<- *Item // Current output channel (starts nil until we have something)
defer close(out)
for {
select {
// Read from the input
case item, ok := <-currentIn:
if !ok {
// The input has been closed. Don't keep trying to read it
currentIn = nil
// If there's nothing pending to write, we're done
if currentItem == nil {
return
}
continue
}
// Were we holding something to write? Put it back.
if currentItem != nil {
heap.Push(&pq, currentItem)
}
// Put our new thing on the queue
heap.Push(&pq, item)
// Turn on the output queue if it's not turned on
currentOut = out
// Grab our best item. We know there's at least one. We just put it there.
currentItem = heap.Pop(&pq).(*Item)
// Write to the output
case currentOut <- currentItem:
// OK, we wrote. Is there anything else?
if len(pq) > 0 {
// Hold onto it for next time
currentItem = heap.Pop(&pq).(*Item)
} else {
// Oh well, nothing to write. Is the input stream done?
if currentIn == nil {
// Then we're done
return
}
// Otherwise, turn off the output stream for now.
currentItem = nil
currentOut = nil
}
}
}
}
Here's an example of using it:
func main() {
// Some items and their priorities.
items := map[string]int{
"banana": 3, "apple": 2, "pear": 4,
}
in := make(chan *Item, 10) // Big input buffer and unbuffered output should give best sort ordering.
out := make(chan *Item) // But the system will "work" for any particular values
// Start the queuing engine!
go queue(in, out)
// Stick some stuff on in another goroutine
go func() {
i := 0
for value, priority := range items {
in <- &Item{
value: value,
priority: priority,
index: i,
}
i++
}
close(in)
}()
// Read the results
for item := range out {
fmt.Printf("%.2d:%s ", item.priority, item.value)
}
fmt.Println()
}
Note that if you run this example, the order will be a little different every time. That's of course expected. It depends on exactly how fast the input and output channels run.
分享
