~ chicken-core (master) fe1448856f6e6a0ef830391dcc3683864faaa089

commit fe1448856f6e6a0ef830391dcc3683864faaa089
Author:     Peter Bex <peter@more-magic.net>
AuthorDate: Mon Sep 28 17:01:10 2015 +0200
Commit:     Peter Bex <peter@more-magic.net>
CommitDate: Mon Sep 28 17:09:26 2015 +0200

    Always call fdset_add for every entry in ##sys#fd-list, to ensure positions match.
    
    In some situations (forced interrupt handler onto primordial thread?)
    fd-list may have items that aren't waiting for an fd to become ready
    for read/write.

diff --git a/scheduler.scm b/scheduler.scm
index f89805fa..8c0976cd 100644
--- a/scheduler.scm
+++ b/scheduler.scm
@@ -393,6 +393,8 @@ EOF
 	(for-each
 	 (lambda (t)
 	   (let ((p (##sys#slot t 11)))
+	     ;; XXX: This should never be false, because otherwise the
+	     ;; thread is not supposed to be on ##sys#fd-list!
 	     (when (pair? p) ; (FD . RWFLAGS)? (can also be mutex or thread)
 	       (let ((i/o (cdr p)))
 		 (case i/o
@@ -407,8 +409,9 @@ EOF
 		    (panic
 		     (sprintf "create-fdset: invalid i/o direction: ~S (fd = ~S)" i/o fd))))))))
 	 (cdar lst))
-	(when (or input output)
-	  ((foreign-lambda void "C_fdset_add" int bool bool) fd input output))
+	;; Our position in fd-list must match fdset array position, so
+	;; always add an fdset entry, even if input & output are #f.
+	((foreign-lambda void "C_fdset_add" int bool bool) fd input output)
 	(loop (cdr lst))))))
 
 (define (fdset-test inf outf i/o)