Add eventloop package

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

eventloop/eventloop.go

@@ -0,0 +1,51 @@
+package eventloop
+
+import (
+	"runtime"
+	"sync"
+)
+
+// Event is receiving notification from loop with Handle() call.
+type Event interface {
+	Handle()
+}
+
+// EventLoop is interface for event loops.
+// Start starting events processing
+// Send adding event to loop
+type EventLoop interface {
+	Start() error
+	Send(Event) error
+}
+
+// ChanLoop is implementation of EventLoop based on channels.
+type ChanLoop struct {
+	events chan Event
+	once   sync.Once
+}
+
+// NewChanLoop returns ChanLoop with internal channel buffer set to q.
+func NewChanLoop(q int) EventLoop {
+	return &ChanLoop{
+		events: make(chan Event, q),
+	}
+}
+
+// Start starting to read events from channel in separate goroutines.
+// All calls after first is no-op.
+func (el *ChanLoop) Start() error {
+	go el.once.Do(func() {
+		// allocate whole OS thread, so nothing can get scheduled over eventloop
+		runtime.LockOSThread()
+		for ev := range el.events {
+			ev.Handle()
+		}
+	})
+	return nil
+}
+
+// Send sends event to channel. Will block if buffer is full.
+func (el *ChanLoop) Send(ev Event) error {
+	el.events <- ev
+	return nil
+}