code: func RunExclusive(ctx context.Context, env subcommands.Env, command func(context.Context) error) error {
  	lockFilePath, drainFilePath, err := computeMutexPaths(env)
  	if err != nil {
  		return err
  	}
  
  	if len(lockFilePath) == 0 {
  		return command(ctx)
  	}
  
  	file, err := os.OpenFile(drainFilePath, os.O_RDONLY|os.O_CREATE, 0666)
  	if err != nil {
  		return err
  	}
  	if err = file.Close(); err != nil {
  		return err
  	}
  
  	// Remove the drain file in case the lock can never be acquired.
  	defer os.Remove(drainFilePath)
  
  	blocker := createLockBlocker(ctx)
  	return fslock.WithBlocking(lockFilePath, blocker, func() error {
  		// Remove the drain file immediately after acquiring the lock in order
  		// to decrease the likelihood that a crash occurs, leaving the drain
  		// file sitting around indefinitely.
  		if err := os.Remove(drainFilePath); err != nil {
  			return err
  		}
  
  		return command(ctx)
  	})
  }
docs: // RunExclusive runs the command with the specified context and environment while
  // holding an exclusive mmutex lock.