cri: handle sandbox/container exit event separately

The event monitor handles exit events one by one. If there is something
wrong about deleting task, it will slow down the terminating Pods. In
order to reduce the impact, the exit event watcher should handle exit
event separately. If it failed, the watcher should put it into backoff
queue and retry it.

Signed-off-by: Wei Fu <fuweid89@gmail.com>

pkg/cri/server/container_start.go

@@ -148,10 +148,8 @@ func (c *criService) StartContainer(ctx context.Context, r *runtime.StartContain
 		return nil, errors.Wrapf(err, "failed to update container %q state", id)
 	}
 
-	// start the monitor after updating container state, this ensures that
-	// event monitor receives the TaskExit event and update container state
-	// after this.
-	c.eventMonitor.startExitMonitor(context.Background(), id, task.Pid(), exitCh)
+	// It handles the TaskExit event and update container state after this.
+	c.eventMonitor.startContainerExitMonitor(context.Background(), id, task.Pid(), exitCh)
 
 	return &runtime.StartContainerResponse{}, nil
 }