Signal handler

Each signal has signal handler function

• 10, 12 is slot for user-defined signal

• When a process executes a signal-handler function, it blocks the signal until the handler terminates.

• Every process should know where the handler function is in
  Process Descriptor.

• All pending signals are processed before go back to user mode (When return from interrupt or exception including system call).

• Signal may remain pending for an unpredictable amount of time.