controller_manager.go

/*
Copyright 2020 Elotl Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package server

import (
	"sync"

	"go.uber.org/atomic"
	"k8s.io/klog"
)

// The ControllerManager was created to make the interaction
// between leader election and controllers easier.  It takes
// care of starting and stopping controllers based on the
// leader elector.
type ControllerManager struct {
	controllers         map[string]Controller
	controllersRunning  *atomic.Bool
	startChan           chan struct{}
	stopChan            chan struct{}
	controllerQuit      chan struct{}
	controllerWaitGroup *sync.WaitGroup
}

func NewControllerManager(controllers map[string]Controller) *ControllerManager {
	return &ControllerManager{
		controllers:         controllers,
		startChan:           make(chan struct{}),
		stopChan:            make(chan struct{}),
		controllersRunning:  atomic.NewBool(false),
		controllerQuit:      nil,
		controllerWaitGroup: nil,
	}
}

func (cm *ControllerManager) StartControllers() {
	cm.startChan <- struct{}{}
}

func (cm *ControllerManager) StopControllers() {
	cm.stopChan <- struct{}{}
}

func (cm *ControllerManager) ControllersRunning() bool {
	return cm.controllersRunning.Load()
}

func (cm *ControllerManager) GetController(name string) (Controller, bool) {
	c, exists := cm.controllers[name]
	return c, exists
}

func (cm *ControllerManager) GetAllControllers() map[string]Controller {
	cpy := map[string]Controller{}
	for k, v := range cm.controllers {
		cpy[k] = v
	}
	return cpy
}

// This doesn't take a quit channel on purpose. This is because if you
// start listening for quit, it becomes difficult to handle starting
// and stopping controllers through the channel as well so we just let
// this goroutine run until the end of the milpa process
func (cm *ControllerManager) Start() {
	for {
		select {
		case <-cm.startChan:
			cm.startControllersHelper()
		case <-cm.stopChan:
			cm.stopControllersHelper()
		}
	}
}

// Our leader election used to tell our controller manager to shutdown
// now this takes care of that. We could simplify the controller
// manager a fair amount...  I'm concerned we'll need a clustered
// system again eventually.
func (cm *ControllerManager) WaitForShutdown(systemShutdown <-chan struct{}, systemWG *sync.WaitGroup) {
	systemWG.Add(1)
	defer systemWG.Done()

	select {
	case <-systemShutdown:
		klog.V(2).Infof("Shutting down controllers")
		cm.StopControllers()
		return
	}
}

func (cm *ControllerManager) startControllersHelper() {
	if cm.ControllersRunning() {
		klog.Warning("Asked to start controllers but they are already running")
		return
	}
	klog.V(2).Info("Starting controllers")
	cm.controllerQuit = make(chan struct{})
	cm.controllerWaitGroup = &sync.WaitGroup{}
	cm.controllersRunning.Store(true)
	for name, controller := range cm.controllers {
		klog.V(2).Infof("Starting %s", name)
		go controller.Start(cm.controllerQuit, cm.controllerWaitGroup)
	}
	klog.V(2).Info("Finished starting controllers")
}

func (cm *ControllerManager) stopControllersHelper() {
	if !cm.ControllersRunning() {
		klog.Warning("Asked to stop controllers but they are not running")
		return
	}
	klog.V(2).Info("Starting to stop controllers")
	close(cm.controllerQuit)
	cm.controllerWaitGroup.Wait()
	cm.controllersRunning.Store(false)
	klog.V(2).Info("All controllers stopped")
}