poll/select: document portability problems not fixed by Gnulib.

* doc/posix-functions/poll.texi: poll does not work well on
pipes under Windows.  It has the same limitations as select on
BeOS.
* doc/posix-functions/select.texi: select does not work well
on pipes under Windows.

2 files changed, 12 insertions, 0 deletions

diff --git a/doc/posix-functions/poll.texi b/doc/posix-functions/poll.texi
index 1c3da5bb2c..da619b99dd 100644
--- a/doc/posix-functions/poll.texi
+++ b/doc/posix-functions/poll.texi
@@ -19,4 +19,12 @@ Mac OS X 10.4.0, AIX 5.3.
 
 Portability problems not fixed by Gnulib:
 @itemize
+@item
+Under BeOS, Gnulib's @code{poll} replacement can only be called on descriptors
+created by the @code{socket} function, not on regular file descriptors.
+
+@item
+Under Windows, when passing a pipe, Gnulib's @code{poll} replacement might
+return 0 even before the timeout has passed.  Programs using it with pipes can
+thus busy wait.
 @end itemize
diff --git a/doc/posix-functions/select.texi b/doc/posix-functions/select.texi
index e59b3cf8e6..c13b30f55a 100644
--- a/doc/posix-functions/select.texi
+++ b/doc/posix-functions/select.texi
@@ -31,6 +31,10 @@ unmodified.
 On BeOS, @code{select} can only be called on descriptors created by the
 @code{socket} function, not on regular file descriptors.
 @item
+Under Windows, when passing a pipe, Gnulib's @code{select} replacement might
+return 0 even before the timeout has passed.  Programs using it with pipes can
+thus busy wait.
+@item
 On Solaris 2.6 and older, @code{select} applied to a file descriptor opened
 for reading and associated with @code{/dev/null} hangs, waiting for input,
 when instead it should return immediately.