"os"
	"os/signal"
	"syscall"

	"istio.io/istio/cni/pkg/cmd"
	"istio.io/istio/pkg/log"
)

func main() {
	// Create context that cancels on termination signal
	ctx, cancel := context.WithCancel(context.Background())
	sigChan := make(chan os.Signal, 1)
	signal.Notify(sigChan, os.Interrupt, syscall.SIGTERM)
	go func(sigChan chan os.Signal, cancel context.CancelFunc) {
		sig := <-sigChan
		log.Infof("Exit signal received: %s", sig)

			target.loggerOnce(context.Background(), err, target.ID().String())
		}
		return err
	}

	if target.natsConn != nil && args.JetStream.Enable {
		var jstream nats.JetStream
		jstream, err = target.natsConn.JetStream()
		if err != nil {
			if err.Error() != nats.ErrNoServers.Error() {
				target.loggerOnce(context.Background(), err, target.ID().String())
			}
			return err
		}

		DB:       db,
		ConnPool: db.ConnPool,
		Context:  context.Background(),
		Clauses:  map[string]clause.Clause{},
	}

	if err == nil && !config.DisableAutomaticPing {
		if pinger, ok := db.ConnPool.(interface{ Ping() error }); ok {
			err = pinger.Ping()
		}
	}

	if err != nil {
		config.Logger.Error(context.Background(), "failed to initialize database, got error %v", err)
	}

	return
}

    Note over client,operation: Response is already sent, can't change it anymore
    opt Tasks
        operation -->> tasks: Send background tasks
    end
    opt Raise other exception
        tasks -->> tasks: Handle exceptions in the background task code
    end
```

/// info | 说明

只会向客户端发送 **一次响应** ，可能是一个错误响应，也可能是来自 *路由函数* 的响应。

在发送了其中一个响应之后，就无法再发送其他响应了。

///

		RunE: func(cmd *cobra.Command, args []string) error {
			kubeClient, err := ctx.CLIClient()
			if err != nil {
				return fmt.Errorf("failed to create Kubernetes client: %v", err)
			}

			return setTag(context.Background(), kubeClient, args[0], revision, ctx.IstioNamespace(), false, cmd.OutOrStdout(), cmd.OutOrStderr())
		},
	}

	cmd.PersistentFlags().BoolVar(&overwrite, "overwrite", false, overrideHelpStr)

import java.net.Socket
import okhttp3.Connection
import okhttp3.Handshake
import okhttp3.HttpUrl
import okhttp3.Protocol
import okhttp3.Route

/**
 * A user that is a connection pool creating connections in the background
 * without an intent to immediately use them.
 */
object PoolConnectionUser : ConnectionUser {
  override fun addPlanToCancel(connectPlan: ConnectPlan) {
  }

	for _, i := range r.Perm(len(disks)) {
		i := i
		wg.Add(1)
		go func() {
			defer wg.Done()
			if disks[i] == nil {
				return
			}
			di, err := disks[i].DiskInfo(context.Background(), DiskInfoOptions{})
			if err != nil || di.Healing {
				// - Do not consume disks which are not reachable
				//   unformatted or simply not accessible for some reason.
				//

		RunE: func(cmd *cobra.Command, args []string) error {
			kubeClient, err := ctx.CLIClientWithRevision(opts.Revision)
			if err != nil {
				return err
			}
			res, err := kubeClient.AllDiscoveryDo(context.Background(), ctx.IstioNamespace(), "debug/clusterz")
			if err != nil {
				return err
			}
			return writeMulticlusterStatus(cmd.OutOrStdout(), res)
		},
	}
	opts.AttachControlPlaneFlags(cmd)
	return cmd
}

import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import javax.annotation.CheckForNull;

/**
 * Phantom reference with a {@code finalizeReferent()} method which a background thread invokes
 * after the garbage collector reclaims the referent. This is a simpler alternative to using a
 * {@link ReferenceQueue}.
 *
 * <p>Unlike a normal phantom reference, this reference will be cleared automatically.

              public Boolean call() {
                return blockingCallable.isRunning();
              }
            },
            directExecutor());

    // Wait for the first task to be started in the background. It will block until we explicitly
    // stop it.
    blockingCallable.waitForStart();

    // Give the second task a chance to (incorrectly) start up while the first task is running.