[m463]

For a DSLR the mirror is independent of the shutter.

Mirror lockup mode is usually used to lower vibration or speed up picture taking, but the shutter still has to actuate.

EDIT: details of 1000D and shutter:

https://en.wikipedia.org/wiki/Canon_EOS_1000D

https://en.wikipedia.org/wiki/Focal-plane_shutter