Sybase libraries treat the asynchronous signal SIGTRAP as a synchronous signal.
If it were treated as an asynchronous signal, the signal would be masked on the calling thread when an application called srv_init or ct_init. That would disable debugging, because many debuggers use SIGTRAP to communicate with the application being debugged. To avoid interfering with debugging, SIGTRAP is treated as a synchronous signal.
UNIX does not allow asynchronous signals to be handled like synchronous signals. You cannot install signal handlers for SIGTRAP using Sybase-provided calls.