About the ambiguous description of sigwait()

Question

If no signal in set is pending at the time of the call, the thread shall be suspended until one or more becomes pending. The signals defined by s

Answer 1

From the signal(7) man page:

Signal Mask and Pending Signals
    A  signal  may  be  blocked,  which means that it will not be delivered
    until it is later unblocked.  Between the time when it is generated and
    when it is delivered a signal is said to be pending.

"Pending" and "blocked" are not mutually exclusive.

Also from the signal(7) man page:

Synchronously Accepting a Signal
    Rather than asynchronously catching a signal via a signal  handler,  it
    is  possible to synchronously accept the signal, that is, to block exe-
    cution until the signal is delivered, at which point the kernel returns
    information about the signal to the caller.  There are two general ways
    to do this:

    * sigwaitinfo(2), sigtimedwait(2),  and  sigwait(3)  suspend  execution
      until  one  of  the signals in a specified set is delivered.  Each of
      these calls returns information about the delivered signal.

So sigaction() is used to allow other code to run until a signal is pending, whereas sigwait() suspends execution of the thread until a signal is pending but blocked.