'Start collecting stats for current batch.
Call before calling forward.'

def tic(self):

    if ((self.step % self.interval) == 0):
        for exe in self.exes:
            for array in exe.arg_arrays:
                array.wait_to_read()
            for array in exe.aux_arrays:
                array.wait_to_read()
        self.queue = []
        self.activated = True
    self.step += 1
