add start code for app callback
Merge branch 'yzliao_v0.2_rdc_callback' of https://github.com/s3lsensor/snowflake into yzliao_v0.2_rdc_callback
Merge branch 'yzliao_v0.2_rdc_callback' of https://github.com/s3lsensor/snowflake into yzliao_v0.2_rdc_callback
fixed bug in app callback, passed compile