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package channels
import "github.com/eapache/queue"
// ResizableChannel implements the Channel interface with a resizable buffer between the input and the output.
// The channel initially has a buffer size of 1, but can be resized by calling Resize().
//
// Resizing to a buffer capacity of None is, unfortunately, not supported and will panic
// (see https://github.com/eapache/channels/issues/1).
// Resizing back and forth between a finite and infinite buffer is fully supported.
type ResizableChannel struct {
input, output chan interface{}
length chan int
capacity, resize chan BufferCap
size BufferCap
buffer *queue.Queue
}
func NewResizableChannel() *ResizableChannel {
ch := &ResizableChannel{
input: make(chan interface{}),
output: make(chan interface{}),
length: make(chan int),
capacity: make(chan BufferCap),
resize: make(chan BufferCap),
size: 1,
buffer: queue.New(),
}
go ch.magicBuffer()
return ch
}
func (ch *ResizableChannel) In() chan<- interface{} {
return ch.input
}
func (ch *ResizableChannel) Out() <-chan interface{} {
return ch.output
}
func (ch *ResizableChannel) Len() int {
return <-ch.length
}
func (ch *ResizableChannel) Cap() BufferCap {
val, open := <-ch.capacity
if open {
return val
} else {
return ch.size
}
}
func (ch *ResizableChannel) Close() {
close(ch.input)
}
func (ch *ResizableChannel) Resize(newSize BufferCap) {
if newSize == None {
panic("channels: ResizableChannel does not support unbuffered behaviour")
}
if newSize < 0 && newSize != Infinity {
panic("channels: invalid negative size trying to resize channel")
}
ch.resize <- newSize
}
func (ch *ResizableChannel) magicBuffer() {
var input, output, nextInput chan interface{}
var next interface{}
nextInput = ch.input
input = nextInput
for input != nil || output != nil {
select {
case elem, open := <-input:
if open {
ch.buffer.Add(elem)
} else {
input = nil
nextInput = nil
}
case output <- next:
ch.buffer.Remove()
case ch.size = <-ch.resize:
case ch.length <- ch.buffer.Length():
case ch.capacity <- ch.size:
}
if ch.buffer.Length() == 0 {
output = nil
next = nil
} else {
output = ch.output
next = ch.buffer.Peek()
}
if ch.size != Infinity && ch.buffer.Length() >= int(ch.size) {
input = nil
} else {
input = nextInput
}
}
close(ch.output)
close(ch.resize)
close(ch.length)
close(ch.capacity)
}
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