Server Threads Model

ClearBox Server is a multithreaded application; its threads perform different tasks.

1. Thread used to control ClearBox Server service. It is created by system only when server runs as a service. It doesn't affect server extension activity.
2. Main application thread, referred as MAIN in this document. At server startup all initialization takes place in this thread. When server has read its parameters from registry, created and initialized server extension object and RADIUS dictionary object (if RADIUS is started), RADIUS and/or TACACS+ manager threads are created, and MAIN thread is blocked until application termination.
3. RADIUS manager thread (referred as RAD). It is created when RADIUS is started. This thread performs a loop, receiving UDP datagrams from sockets, reading packets from network buffer, writing packets to network buffer and sending socket data. It's terminated on request of MAIN thread when server stops.
4. TACACS+ manager thread (referred as TAC). It is created when TACACS+ is started. This thread performs a loop, accepting client TCP connections, reading data from sockets, reading packets from buffer and writing them to buffer, sending data back to TCP clients. It's terminated on request of MAIN thread when server stops.
5. RADIUS proxy manager thread (referred as PROX). It is created when RADIUS proxy manager is started and RADIUS packet forwarding is enabled. This thread receives tasks for packet forwarding from WORK thread, sends/receives packets from remote hosts and returns them to RAD thread.
6. Pool of threads that perform main processing of TACACS+/RADIUS packets. They are referred as WORK. These threads stay blocked until they receive task to process a packet. After a packet is processed, it is returned to TAC/RAD thread, and WORK thread is blocked again. Note that several WORK threads may exist, depending on server configuration. All calls to server extension methods for one packet processing are executed in context of one WORK thread.
7. Schedule agent thread (referred as SCHEDULE). It's started from MAIN thread at startup and performs periodic scheduled tasks.
8. Synchronization agent thread (referred as SYNC). It's started from MAIN thread at startup and performs synchronization of extension's users database with actual users list on a NAS.
9. Monitoring agent thread (referred as MONITOR). It's started from MAIN thread at startup and is responsible for communications with Server Manager.

Server extension is a free-threaded COM-server, so no call synchronization is performed by COM. Server extension must protect resources shared between several threads as extension's methods are called from almost all the threads listed above. Extension may use critical sections as a lightweight mechanism for this purpose.