The Framework of BESIII Event Filter

The BES III (Beijing Spectrometer III) is a general purpose detector at BEPC II (Beijing Electron Positron Collider II) currently under construction in Beijing. Based on the framework of Atlas TDAQ (trigger and data acquisition) software, the BESIII event filter software consists of the EFD (event filter dataflow) component and the PT (processing task) component which invokes the offline event selection procedure to analyze the events and make decisions. The primary function of event filter is to fetch full events from the event builder, analyze them with physics event selection algorithms, and send the accepted events to the event storage sub-system. In particular, in order to increase system reliability, two methods are introduced: (1) timeout PT will be killed by the corresponding EFD. (2) Standby lines will be automatically opened when normal lines cannot satisfy the rated data flow. This paper focuses on the framework architecture, system reliability and stability of the BES III event filter software.