Add descriptions about signal queue.

1 files changed, 24 insertions, 0 deletions

diff --git a/lib/libc/sys/sigwait.2 b/lib/libc/sys/sigwait.2
index 2d635cbb2cd2..632d9919e031 100644
--- a/lib/libc/sys/sigwait.2
+++ b/lib/libc/sys/sigwait.2
@@ -58,6 +58,24 @@ The signals specified by
 .Fa set
 should be blocked at the time of the call to
 .Fn sigwait .
+.Pp
+If more than one thread is using
+.Fn sigwait
+to wait for the same signal, no more than one of these threads will return from
+.Fn sigwait
+with the signal number. If more than a single thread is blocked in
+.Fn sigwait
+for a signal when that signal is generated for the process, it is unspecified
+which of the waiting threads returns from
+.Fn sigwait .
+If the signal is generated for a specific thread, as by
+.Fn pthread_kill ,
+only that thread will return.
+.Pp
+Should any of the multiple pending signals in the range SIGRTMIN to SIGRTMAX be
+selected, it will be the lowest numbered one. The selection order between realtime
+and non-realtime signals, or between multiple pending non-realtime signals,
+is unspecified.
 .Sh RETURN VALUES
 If successful,
 .Fn sigwait
@@ -75,8 +93,14 @@ The
 .Fa set
 argument
 specifies one or more invalid signal numbers.
+.It Bq Er EFAULT
+Any arguments point outside the allocated address space or there is a
+memory protection fault.
 .El
 .Sh SEE ALSO
+.Xr sigtimedwait 2 ,
+.Xr sigwaitinfo 2 ,
+.Xr sigqueue 2 ,
 .Xr sigaction 2 ,
 .Xr sigpending 2 ,
 .Xr sigsuspend 2 ,