About killcursors

I’ve got this log like this, and I don’t know how to interpret this log.

killcursors […] numYields:0 locks:{ Global: { acquireCount: { r: 2 } }, Database: { acquireCount: { r: 1 } }, Collection: { acquireCount: { r: 1 } } } 4176ms

And I’ve confirmed that killcursors are implemented in client-side, but have not called killcursors in business logic.

Is there a case when mongodb driver calls killcursors itself?