func HandleEngineEvents(taskEngine engine.TaskEngine, client api.ECSClient, saver statemanager.Saver) {
	statesaver = saver
	for {
		taskEvents, containerEvents := taskEngine.TaskEvents()

		for taskEvents != nil && containerEvents != nil {
			select {
			case event, open := <-containerEvents:
				if !open {
					containerEvents = nil
					log.Error("Container events closed")
					break
				}

				AddContainerEvent(event, client)
			case event, open := <-taskEvents:
				if !open {
					taskEvents = nil
					log.Crit("Task events closed")
					break
				}

				AddTaskEvent(event, client)
			}
		}
	}
}

// FinalSave should be called immediately before exiting, and only before
// exiting, in order to flush tasks to disk. It waits a short timeout for state
// to settle if necessary. If unable to reach a steady-state and save within
// this short timeout, it returns an error
func FinalSave(saver statemanager.Saver, taskEngine engine.TaskEngine) error {
	engineDisabled := make(chan error)

	disableTimer := time.AfterFunc(engineDisableTimeout, func() {
		engineDisabled <- errors.New("Timed out waiting for TaskEngine to settle")
	})

	go func() {
		log.Debug("Shutting down task engine")
		taskEngine.Disable()
		disableTimer.Stop()
		engineDisabled <- nil
	}()

	disableErr := <-engineDisabled

	stateSaved := make(chan error)
	saveTimer := time.AfterFunc(finalSaveTimeout, func() {
		stateSaved <- errors.New("Timed out trying to save to disk")
	})
	go func() {
		log.Debug("Saving state before shutting down")
		stateSaved <- saver.ForceSave()
		saveTimer.Stop()
	}()

	saveErr := <-stateSaved

	if disableErr != nil || saveErr != nil {
		return utils.NewMultiError(disableErr, saveErr)
	}
	return nil
}

func addNonstoppedTasks(tasks []*api.Task, taskEngine engine.TaskEngine) bool {
	allTasksOk := true
	for _, task := range tasks {
		if task.DesiredStatus == api.TaskStopped {
			continue
		}
		err := taskEngine.AddTask(task)
		if err != nil {
			log.Warn("Could not add task; taskengine probably disabled")
			// Don't ack
			allTasksOk = false
		}
	}
	return allTasksOk
}

// AcsWsUrl returns the websocket url for ACS given the endpoint.
func AcsWsUrl(endpoint, cluster, containerInstanceArn string, taskEngine engine.TaskEngine) string {
	acsUrl := endpoint
	if endpoint[len(endpoint)-1] != '/' {
		acsUrl += "/"
	}
	acsUrl += "ws"
	query := url.Values{}
	query.Set("clusterArn", cluster)
	query.Set("containerInstanceArn", containerInstanceArn)
	query.Set("agentHash", version.GitHashString())
	query.Set("agentVersion", version.Version)
	query.Set("seqNum", strconv.FormatInt(SequenceNumber.Get(), 10))
	if dockerVersion, err := taskEngine.Version(); err == nil {
		query.Set("dockerVersion", dockerVersion)
	}
	return acsUrl + "?" + query.Encode()
}

// acsWsURL returns the websocket url for ACS given the endpoint
func acsWsURL(endpoint, cluster, containerInstanceArn string, taskEngine engine.TaskEngine, acsSessionState sessionState) string {
	acsUrl := endpoint
	if endpoint[len(endpoint)-1] != '/' {
		acsUrl += "/"
	}
	acsUrl += "ws"
	query := url.Values{}
	query.Set("clusterArn", cluster)
	query.Set("containerInstanceArn", containerInstanceArn)
	query.Set("agentHash", version.GitHashString())
	query.Set("agentVersion", version.Version)
	query.Set("seqNum", "1")
	if dockerVersion, err := taskEngine.Version(); err == nil {
		query.Set("dockerVersion", dockerVersion)
	}
	query.Set(sendCredentialsURLParameterName, acsSessionState.getSendCredentialsURLParameter())
	return acsUrl + "?" + query.Encode()
}

func _main() int {
	defer log.Flush()
	versionFlag := flag.Bool("version", false, "Print the agent version information and exit")
	acceptInsecureCert := flag.Bool("k", false, "Do not verify ssl certs")
	logLevel := flag.String("loglevel", "", "Loglevel: [<crit>|<error>|<warn>|<info>|<debug>]")
	flag.Parse()

	logger.SetLevel(*logLevel)

	log.Infof("Starting Agent: %v", version.String())

	log.Info("Loading configuration")
	cfg, err := config.NewConfig()
	// Load cfg before doing 'versionFlag' so that it has the DOCKER_HOST
	// variable loaded if needed
	if *versionFlag {
		versionableEngine := engine.NewTaskEngine(cfg)
		version.PrintVersion(versionableEngine)
		return exitcodes.ExitSuccess
	}

	if err != nil {
		log.Criticalf("Error loading config: %v", err)
		// All required config values can be inferred from EC2 Metadata, so this error could be transient.
		return exitcodes.ExitError
	}
	log.Debug("Loaded config: " + cfg.String())

	var currentEc2InstanceID, containerInstanceArn string
	var taskEngine engine.TaskEngine

	if cfg.Checkpoint {
		log.Info("Checkpointing is enabled. Attempting to load state")
		var previousCluster, previousEc2InstanceID, previousContainerInstanceArn string
		previousTaskEngine := engine.NewTaskEngine(cfg)
		// previousState is used to verify that our current runtime configuration is
		// compatible with our past configuration as reflected by our state-file
		previousState, err := initializeStateManager(cfg, previousTaskEngine, &previousCluster, &previousContainerInstanceArn, &previousEc2InstanceID, acshandler.SequenceNumber)
		if err != nil {
			log.Criticalf("Error creating state manager: %v", err)
			return exitcodes.ExitTerminal
		}

		err = previousState.Load()
		if err != nil {
			log.Criticalf("Error loading previously saved state: %v", err)
			return exitcodes.ExitTerminal
		}

		if previousCluster != "" {
			// TODO Handle default cluster in a sane and unified way across the codebase
			configuredCluster := cfg.Cluster
			if configuredCluster == "" {
				log.Debug("Setting cluster to default; none configured")
				configuredCluster = config.DEFAULT_CLUSTER_NAME
			}
			if previousCluster != configuredCluster {
				log.Criticalf("Data mismatch; saved cluster '%v' does not match configured cluster '%v'. Perhaps you want to delete the configured checkpoint file?", previousCluster, configuredCluster)
				return exitcodes.ExitTerminal
			}
			cfg.Cluster = previousCluster
			log.Infof("Restored cluster '%v'", cfg.Cluster)
		}

		if instanceIdentityDoc, err := ec2.GetInstanceIdentityDocument(); err == nil {
			currentEc2InstanceID = instanceIdentityDoc.InstanceId
		} else {
			log.Criticalf("Unable to access EC2 Metadata service to determine EC2 ID: %v", err)
		}

		if previousEc2InstanceID != "" && previousEc2InstanceID != currentEc2InstanceID {
			log.Warnf("Data mismatch; saved InstanceID '%v' does not match current InstanceID '%v'. Overwriting old datafile", previousEc2InstanceID, currentEc2InstanceID)

			// Reset taskEngine; all the other values are still default
			taskEngine = engine.NewTaskEngine(cfg)
		} else {
			// Use the values we loaded if there's no issue
			containerInstanceArn = previousContainerInstanceArn
			taskEngine = previousTaskEngine
		}
	} else {
		log.Info("Checkpointing not enabled; a new container instance will be created each time the agent is run")
		taskEngine = engine.NewTaskEngine(cfg)
	}

	stateManager, err := initializeStateManager(cfg, taskEngine, &cfg.Cluster, &containerInstanceArn, &currentEc2InstanceID, acshandler.SequenceNumber)
	if err != nil {
		log.Criticalf("Error creating state manager: %v", err)
		return exitcodes.ExitTerminal
	}

	credentialProvider := auth.NewBasicAWSCredentialProvider()
	awsCreds := auth.ToSDK(credentialProvider)
	// Preflight request to make sure they're good
	if preflightCreds, err := awsCreds.Credentials(); err != nil || preflightCreds.AccessKeyID == "" {
		if preflightCreds != nil {
			log.Warnf("Error getting valid credentials (AKID %v): %v", preflightCreds.AccessKeyID, err)
		} else {
			log.Warnf("Error getting preflight credentials: %v", err)
		}
//.........这里部分代码省略.........

func _main() int {
	defer log.Flush()
	flagset := flag.NewFlagSet("Amazon ECS Agent", flag.ContinueOnError)
	versionFlag := flagset.Bool("version", false, "Print the agent version information and exit")
	logLevel := flagset.String("loglevel", "", "Loglevel: [<crit>|<error>|<warn>|<info>|<debug>]")
	acceptInsecureCert := flagset.Bool("k", false, "Disable SSL certificate verification. We do not recommend setting this option.")
	licenseFlag := flagset.Bool("license", false, "Print the LICENSE and NOTICE files and exit")
	blackholeEc2Metadata := flagset.Bool("blackhole-ec2-metadata", false, "Blackhole the EC2 Metadata requests. Setting this option can cause the ECS Agent to fail to work properly.  We do not recommend setting this option")
	err := flagset.Parse(os.Args[1:])
	if err != nil {
		return exitcodes.ExitTerminal
	}

	if *licenseFlag {
		license := utils.NewLicenseProvider()
		text, err := license.GetText()
		if err != nil {
			fmt.Fprintln(os.Stderr, err)
			return exitcodes.ExitError
		}
		fmt.Println(text)
		return exitcodes.ExitSuccess
	}

	logger.SetLevel(*logLevel)
	ec2MetadataClient := ec2.DefaultClient
	if *blackholeEc2Metadata {
		ec2MetadataClient = ec2.NewBlackholeEC2MetadataClient()
	}

	log.Infof("Starting Agent: %s", version.String())
	if *acceptInsecureCert {
		log.Warn("SSL certificate verification disabled. This is not recommended.")
	}
	log.Info("Loading configuration")
	cfg, cfgErr := config.NewConfig(ec2MetadataClient)
	// Load cfg and create Docker client before doing 'versionFlag' so that it has the DOCKER_HOST variable loaded if needed
	clientFactory := dockerclient.NewFactory(cfg.DockerEndpoint)
	dockerClient, err := engine.NewDockerGoClient(clientFactory, *acceptInsecureCert, cfg)
	if err != nil {
		log.Criticalf("Error creating Docker client: %v", err)
		return exitcodes.ExitError
	}

	ctx := context.Background()
	// Create the DockerContainerChange event stream for tcs
	containerChangeEventStream := eventstream.NewEventStream(ContainerChangeEventStream, ctx)
	containerChangeEventStream.StartListening()

	// Create credentials manager. This will be used by the task engine and
	// the credentials handler
	credentialsManager := credentials.NewManager()
	// Create image manager. This will be used by the task engine for saving image states
	state := dockerstate.NewDockerTaskEngineState()
	imageManager := engine.NewImageManager(cfg, dockerClient, state)
	if *versionFlag {
		versionableEngine := engine.NewTaskEngine(cfg, dockerClient, credentialsManager, containerChangeEventStream, imageManager, state)
		version.PrintVersion(versionableEngine)
		return exitcodes.ExitSuccess
	}

	sighandlers.StartDebugHandler()

	if cfgErr != nil {
		log.Criticalf("Error loading config: %v", err)
		// All required config values can be inferred from EC2 Metadata, so this error could be transient.
		return exitcodes.ExitError
	}
	log.Debug("Loaded config: " + cfg.String())

	var currentEc2InstanceID, containerInstanceArn string
	var taskEngine engine.TaskEngine

	if cfg.Checkpoint {
		log.Info("Checkpointing is enabled. Attempting to load state")
		var previousCluster, previousEc2InstanceID, previousContainerInstanceArn string
		previousTaskEngine := engine.NewTaskEngine(cfg, dockerClient, credentialsManager, containerChangeEventStream, imageManager, state)
		// previousState is used to verify that our current runtime configuration is
		// compatible with our past configuration as reflected by our state-file
		previousState, err := initializeStateManager(cfg, previousTaskEngine, &previousCluster, &previousContainerInstanceArn, &previousEc2InstanceID)
		if err != nil {
			log.Criticalf("Error creating state manager: %v", err)
			return exitcodes.ExitTerminal
		}

		err = previousState.Load()
		if err != nil {
			log.Criticalf("Error loading previously saved state: %v", err)
			return exitcodes.ExitTerminal
		}

		if previousCluster != "" {
			// TODO Handle default cluster in a sane and unified way across the codebase
			configuredCluster := cfg.Cluster
			if configuredCluster == "" {
				log.Debug("Setting cluster to default; none configured")
				configuredCluster = config.DefaultClusterName
			}
			if previousCluster != configuredCluster {
				log.Criticalf("Data mismatch; saved cluster '%v' does not match configured cluster '%v'. Perhaps you want to delete the configured checkpoint file?", previousCluster, configuredCluster)
//.........这里部分代码省略.........