Add initial controller boilerplate and example controller

Signed-off-by: Monis Khan <mok@vmware.com>

internal/controller/manager.go

@@ -0,0 +1,59 @@
+/*
+Copyright 2020 VMware, Inc.
+SPDX-License-Identifier: Apache-2.0
+*/
+
+package controller
+
+import (
+	"context"
+	"sync"
+
+	"k8s.io/klog/v2"
+)
+
+type Manager interface {
+	Start(ctx context.Context)
+	WithController(controller Controller, workers int) Manager
+}
+
+func NewManager() Manager {
+	return &controllerManager{}
+}
+
+// runnableController represents single controller runnable configuration.
+type runnableController struct {
+	controller Controller
+	workers    int
+}
+
+type controllerManager struct {
+	controllers []runnableController
+}
+
+var _ Manager = &controllerManager{}
+
+func (c *controllerManager) WithController(controller Controller, workers int) Manager {
+	c.controllers = append(c.controllers, runnableController{
+		controller: controller,
+		workers:    workers,
+	})
+	return c
+}
+
+// Start will run all managed controllers and block until all controllers shutdown.
+// When the context passed is cancelled, all controllers are signalled to shutdown.
+func (c *controllerManager) Start(ctx context.Context) {
+	var wg sync.WaitGroup
+	wg.Add(len(c.controllers))
+	for i := range c.controllers {
+		idx := i
+		go func() {
+			r := c.controllers[idx]
+			defer klog.InfoS("controller terminated", "controller", r.controller.Name())
+			defer wg.Done()
+			r.controller.Run(ctx, r.workers)
+		}()
+	}
+	wg.Wait()
+}