Hello,
As of Guile 2.2.3, the Scheme-level ‘select’ can return non-empty sets
when the C-level ‘select’ returns EINTR or EAGAIN. The program below
illustrates this:
--8<---------------cut here---------------start------------->8---
(use-modules (ice-9 match))
(sigaction SIGINT (lambda args
(pk 'signal! args)))
(let ((target (getpid)))
(match (primitive-fork)
((? zero?)
(sleep 4)
(kill target SIGINT)
(primitive-exit 0))
(_ #t)))
(match (select (list (current-input-port)) '() '())
(((port) () ())
(pk 'reading-from port)
(read-char port))
(lst
(pk 'done lst)))
--8<---------------cut here---------------end--------------->8---
On 2.2.3, it prints:
--8<---------------cut here---------------start------------->8---
$ guile select.scm
;;; (signal! (2))
;;; (reading-from #<input: file /dev/pts/9>)
--8<---------------cut here---------------end--------------->8---
>From there on it’s stuck in a read(0, …) call.
The attached patch fixes it by clearing the returned FD sets on
EINTR/EAGAIN.
(Besides it seems that select(2) never returns EAGAIN.)
I’m not sure how to write a test for this; the one above is
timing-sensitive, which wouldn’t be great.
Thoughts?
Ludo’.
diff --git a/libguile/filesys.c b/libguile/filesys.c
index e39dc4a0d..05dd2bd16 100644
--- a/libguile/filesys.c
+++ b/libguile/filesys.c
@@ -1,5 +1,5 @@
/* Copyright (C) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2004, 2006,
- * 2009, 2010, 2011, 2012, 2013, 2014, 2016, 2017 Free Software Foundation, Inc.
+ * 2009, 2010, 2011, 2012, 2013, 2014, 2016, 2017, 2018 Free Software Foundation, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
@@ -900,10 +900,20 @@ SCM_DEFINE (scm_select, "select", 3, 2, 0,
int rv = scm_std_select (max_fd + 1,
&read_set, &write_set, &except_set,
time_ptr);
- /* Let EINTR / EAGAIN cause a return to the user and let them loop
- to run any asyncs that might be pending. */
- if (rv < 0 && errno != EINTR && errno != EAGAIN)
- SCM_SYSERROR;
+ if (rv < 0)
+ {
+ /* Let EINTR / EAGAIN cause a return to the user and let them
+ loop to run any asyncs that might be pending. */
+ if (errno != EINTR && errno != EAGAIN)
+ SCM_SYSERROR;
+ else
+ {
+ /* Return empty sets. */
+ FD_ZERO (&read_set);
+ FD_ZERO (&write_set);
+ FD_ZERO (&except_set);
+ }
+ }
}
return scm_list_3 (retrieve_select_type (&read_set, read_ports_ready, reads),
