Note that you must not use @code{sigprocmask} in multi-threaded processes,
because each thread has its own signal mask and there is no single process
signal mask. According to POSIX, the behavior of @code{sigprocmask} in a
-multi-threaded process is ``unspeficied''.
+multi-threaded process is ``unspecified''.
Instead, use @code{pthread_sigmask}.
@ifset linuxthreads
@xref{Threads and Signal Handling}.