meanwhile= in the meantime, during (a span of time) I am going to sleep, you can check my library meanwhile(in the meantime, during the time I use for my sleep).

Meanwhile means during certain interval of time or at the same time . i.e My girlfriend was watching the t.v meanwhile i was listening to some old spanish music .... so basically it refers to some previous statement .

"Meanwhile" indicates an action at the same time, but in a different place. "In the meantime" indicates one activity that was done while waiting for another activity to finish. These are very different meanings.