Among the devices on which an event happened on 2016/5/1, how many of them are used by a male user?
on 2016/5/1 refers to timestamp = '2016-05-01'; male refers to gender = 'M';
SELECT COUNT(T1.device_id) FROM events AS T1 INNER JOIN gender_age AS T2 ON T1.device_id = T2.device_id WHERE T1.timestamp = '2016-05-01' AND T2.gender = 'M'