Fix ‘epoll instance is dead #61’

fibers/epoll.scm

@@ -1,6 +1,7 @@
 ;; epoll
 
 ;;;; Copyright (C) 2016 Andy Wingo <wingo@pobox.com>
+;;;; Copyright (C) 2022 Maxime Devos <maximedevos@telenet.be>
 ;;;; 
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -135,7 +136,12 @@ epoll wait (if appropriate)."
     ('waiting
      (primitive-epoll-wake (fileno (epoll-wake-write-pipe epoll))))
     ('not-waiting #t)
-    ('dead (error "epoll instance is dead"))))
+    ;; This can happen if a fiber was waiting on a condition and
+    ;; run-fibers completes before the fiber completes and afterwards
+    ;; the condition is signalled.  In that case, we don't have to
+    ;; resurrect the fiber or something, we can just do nothing.
+    ;; (Bug report: https://github.com/wingo/fibers/issues/61)
+    ('dead #t)))
 
 (define (epoll-default-folder fd events seed)
   (acons fd events seed))

tests/conditions.scm

@@ -1,6 +1,7 @@
 ;; Fibers: cooperative, event-driven user-space threads.
 
 ;;;; Copyright (C) 2016 Free Software Foundation, Inc.
+;;;; Copyright (C) 2022 Maxime Devos <maximedevos@telenet.be>
 ;;;;
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -21,6 +22,7 @@
   #:use-module (fibers)
   #:use-module (fibers conditions)
   #:use-module (fibers operations)
+  #:use-module (fibers scheduler)
   #:use-module (fibers timers))
 
 (define failed? #f)
@@ -78,4 +80,22 @@
                              (wait cv)
                              #t))
 
+;; Make a condition, wait for it inside a fiber, let the fiber abruptly
+;; terminate and signal the condition afterwards.  This tests for the bug
+;; noticed at <https://github.com/wingo/fibers/issues/61>.
+(assert-equal #t
+	      (let ((cv (make-condition)))
+		(run-fibers
+		 (lambda ()
+		   (spawn-fiber (lambda () (wait cv)))
+		   (yield-current-task)) ; let the other fiber wait forever
+		 ;; This test relies on not draining -- this is the default,
+		 ;; but let's make this explicit.
+		 #:drain? #false ;
+		 ;; For simplicity, disable concurrency and preemption.
+		 ;; That way, we can use 'yield-current-task' instead of an
+		 ;; arbitrary sleep time.
+		 #:hz 0 #:parallelism 1)
+		(signal-condition! cv)))
+
 (exit (if failed? 1 0))