Synchronous Signals

Traps, such as SIGILL, SIGFPE, and SIGSEGV, result from an operation on the thread, such as dividing by zero or making reference to nonexistent memory. A trap is handled only by the thread that caused the trap. Several threads in a process can generate and handle the same type of trap simultaneously.

The idea of signals to individual threads is easily extended for synchronously generated signals. The handler is invoked on the thread that generated the synchronous signal.

However, if the process chooses not to establish an appropriate signal handler, the default action is taken when a trap occurs. The default action occurs even if the offending thread is blocked on the generated signal. The default action for such signals is to terminate the process, perhaps with a core dump.

Such a synchronous signal usually means that something is seriously wrong with the whole process, not just with a thread. In this case, terminating the process is often a good choice.