new driver: kubernetes

Tested with `kind` and GKE.

Note: "nodes" shown in `docker buildx ls` are unrelated to Kubernetes "nodes".
Probably buildx should come up with an alternative term.

Usage:

  $ kind create cluster
  $ export KUBECONFIG="$(kind get kubeconfig-path --name="kind")"

  $ docker buildx create --driver kubernetes --driver-opt replicas=3 --use
  $ docker buildx build -t foo --load .

`--load` loads the image into the local Docker.

Driver opts:

  - `image=IMAGE` - Sets the container image to be used for running buildkit.
  - `namespace=NS` - Sets the Kubernetes namespace. Defaults to the current namespace.
  - `replicas=N` - Sets the number of `Pod` replicas. Defaults to 1.
  - `rootless=(true|false)` - Run the container as a non-root user without `securityContext.privileged`. Defaults to false.
  - `loadbalance=(sticky|random)` - Load-balancing strategy. If set to "sticky", the pod is chosen using the hash of the context path. Defaults to "sticky"

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

vendor/github.com/docker/spdystream/priority.go

@@ -0,0 +1,98 @@
+package spdystream
+
+import (
+	"container/heap"
+	"sync"
+
+	"github.com/docker/spdystream/spdy"
+)
+
+type prioritizedFrame struct {
+	frame    spdy.Frame
+	priority uint8
+	insertId uint64
+}
+
+type frameQueue []*prioritizedFrame
+
+func (fq frameQueue) Len() int {
+	return len(fq)
+}
+
+func (fq frameQueue) Less(i, j int) bool {
+	if fq[i].priority == fq[j].priority {
+		return fq[i].insertId < fq[j].insertId
+	}
+	return fq[i].priority < fq[j].priority
+}
+
+func (fq frameQueue) Swap(i, j int) {
+	fq[i], fq[j] = fq[j], fq[i]
+}
+
+func (fq *frameQueue) Push(x interface{}) {
+	*fq = append(*fq, x.(*prioritizedFrame))
+}
+
+func (fq *frameQueue) Pop() interface{} {
+	old := *fq
+	n := len(old)
+	*fq = old[0 : n-1]
+	return old[n-1]
+}
+
+type PriorityFrameQueue struct {
+	queue        *frameQueue
+	c            *sync.Cond
+	size         int
+	nextInsertId uint64
+	drain        bool
+}
+
+func NewPriorityFrameQueue(size int) *PriorityFrameQueue {
+	queue := make(frameQueue, 0, size)
+	heap.Init(&queue)
+
+	return &PriorityFrameQueue{
+		queue: &queue,
+		size:  size,
+		c:     sync.NewCond(&sync.Mutex{}),
+	}
+}
+
+func (q *PriorityFrameQueue) Push(frame spdy.Frame, priority uint8) {
+	q.c.L.Lock()
+	defer q.c.L.Unlock()
+	for q.queue.Len() >= q.size {
+		q.c.Wait()
+	}
+	pFrame := &prioritizedFrame{
+		frame:    frame,
+		priority: priority,
+		insertId: q.nextInsertId,
+	}
+	q.nextInsertId = q.nextInsertId + 1
+	heap.Push(q.queue, pFrame)
+	q.c.Signal()
+}
+
+func (q *PriorityFrameQueue) Pop() spdy.Frame {
+	q.c.L.Lock()
+	defer q.c.L.Unlock()
+	for q.queue.Len() == 0 {
+		if q.drain {
+			return nil
+		}
+		q.c.Wait()
+	}
+	frame := heap.Pop(q.queue).(*prioritizedFrame).frame
+	q.c.Signal()
+	return frame
+}
+
+func (q *PriorityFrameQueue) Drain() {
+	q.c.L.Lock()
+	defer q.c.L.Unlock()
+	q.drain = true
+	q.c.Broadcast()
+}