'Invokes global barrier among all worker nodes.
For example, assume there are `n` machines. We would like machine `0` to first
`init` the values and then have all the workers `pull` the initialized value.
Before pulling, we can place invoke `_barrier()` to guarantee that the
initialization is finished.'

def _barrier(self):

    check_call(_LIB.MXKVStoreBarrier(self.handle))
