Infinite loop on broken pipe

I tried the command line that you mention but nothing happens. I tried it on Mac OS X and Debian and it was terminating as usual:

$ echo | ikarus | (read;read)
$ echo | ikarus | (read;read)
$ echo | ikarus | (read;read)

Can you list what happens when you issue that command line. Also, can you provide more information about your operating system/environment. Thanks.

On Sun, 2008-07-27 at 07:02 +0000, Abdulaziz Ghuloum wrote:
> I tried the command line that you mention but nothing happens.

The problem happens to me on Ubuntu 8.04.

$ strace ikarus 2>/tmp/ikarus-read-read.strace | (read;read)

ikarus-read-read.strace:

execve("/home/d/bin/ikarus", ["ikarus"], [/* 45 vars */]) = 0
[...all the start-up stuff...]
write(1, "Ikarus Scheme version 0.0.3+ (re"..., 62) = 62
write(1, "\n", 1) = 1
write(1, "Copyright (c) 2006-2008 Abdulazi"..., 43) = 43
write(1, ">", 1) = -1 EPIPE (Broken pipe)
write(1, ">", 1) = -1 EPIPE (Broken pipe)
write(1, ">>", 2) = -1 EPIPE (Broken pipe)
write(1, ">>", 2) = -1 EPIPE (Broken pipe)
write(1, ">>>", 3) = -1 EPIPE (Broken pipe)
write(1, ">>>", 3) = -1 EPIPE (Broken pipe)
write(1, ">>>>", 4) = -1 EPIPE (Broken pipe)
write(1, ">>>>", 4) = -1 EPIPE (Broken pipe)
write(1, ">>>>>", 5) = -1 EPIPE (Broken pipe)
write(1, ">>>>>", 5) = -1 EPIPE (Broken pipe)
write(1, ">>>>>>", 6) = -1 EPIPE (Broken pipe)
write(1, ">>>>>>", 6) = -1 EPIPE (Broken pipe)
write(1, ">>>>>>>", 7) = -1 EPIPE (Broken pipe)
write(1, ">>>>>>>", 7) = -1 EPIPE (Broken pipe)
write(1, ">>>>>>>>", 8) = -1 EPIPE (Broken pipe)
write(1, ">>>>>>>>", 8) = -1 EPIPE (Broken pipe)
[...]
write(1, ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>"..., 4775) = -1 EPIPE (Broken pipe)
write(1, ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>"..., 4775) = -1 EPIPE (Broken pipe)
write(1, ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>"..., 4776) = -1 EPIPE (Broken pipe)
write(1, ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>"..., 4776) = -1 EPIPE (Broken pipe)

The cause is in ikarus.cafe.ss. The (read;read) consumes the first two
lines of the banner, then when (display-prompt 0) is attempted it raises
a broken pipe exception, the handler then attempts (flush-output-port
(console-output-port)) which raises a broken pipe exception, the next
handler invokes the reset continuation which loops back to attempting
another (display-prompt 0).

On Sun, 2008-07-27 at 03:30 -0700, Derick Eddington wrote:
> The cause is in ikarus.cafe.ss.

Do you think the handlers which do the reset behavior should only be
around the (eval-proc x)? That way any bizarre exceptions raised by
non- user code propagate to the base handler which just exits.

On Sun, 2008-07-27 at 04:07 -0700, Derick Eddington wrote:
> Do you think the handlers which do the reset behavior should only be
> around the (eval-proc x)?

No. Reader exceptions need to reset the REPL too.

There are two other situations that make the cafe go berserk. Try:
  (close-output-port (current-output-port))
and
  (close-input-port (current-input-port))

I think that the cafe handler around "read" should only handle &lexical and &interrupted conditions and propagate the rest upwards while the handler around eval should trap all conditions. Need to try it out.

On Sun, 2008-07-27 at 16:39 +0000, Abdulaziz Ghuloum wrote:
> There are two other situations that make the cafe go berserk. Try:
> (close-output-port (current-output-port))
> and
> (close-input-port (current-input-port))

Hehe :)

> I think that the cafe handler around "read" should only handle &lexical
> and &interrupted conditions and propagate the rest upwards while the
> handler around eval should trap all conditions. Need to try it out.

I've tried this:

=== modified file 'scheme/ikarus.cafe.ss'
--- scheme/ikarus.cafe.ss 2008-07-13 03:05:45 +0000
+++ scheme/ikarus.cafe.ss 2008-07-28 02:34:31 +0000
@@ -53,48 +53,58 @@
             (display ">" (console-output-port))
             (display-prompt (fx+ i 1))))))

- (define my-read
- (lambda (k)
- (parameterize ([interrupt-handler
- (lambda ()
- (flush-output-port (console-output-port))
- (reset-input-port! (console-input-port))
- (newline (console-output-port))
- (k))])
- (read (console-input-port)))))
-
+ (define (print-ex ex)
+ (flush-output-port (console-output-port))
+ (display "Unhandled exception\n" (console-error-port))
+ (print-condition ex (console-error-port)))
+
+ (define (reset k)
+ (reset-input-port! (console-input-port))
+ (k))
+
   (define wait
     (lambda (eval-proc escape-k)
       (call/cc
         (lambda (k)
- (with-exception-handler
- (lambda (con)
- (reset-input-port! (console-input-port))
- (k (void)))
- (lambda ()
- (with-exception-handler
- (lambda (con)
- (flush-output-port (console-output-port))
- (display "Unhandled exception\n" (console-error-port))
- (print-condition con (console-error-port))
- (when (interrupted-condition? con)
- (raise-continuable con)))
- (lambda ()
- (display-prompt 0)
- (let ([x (my-read k)])
- (cond
- [(eof-object? x)
- (newline (console-output-port))
- (escape-k (void))]
- [else
- (call-with-values
- (lambda () (eval-proc x))
- (lambda v*
- (unless (andmap (lambda (v) (eq? v (void))) v*)
- (for-each
- (lambda (v)
- (pretty-print v (console-output-port)))
- v*))))]))))))))
+ (display-prompt 0)
+ (let ([x (with-exception-handler
+ (lambda (ex)
+ (cond [(lexical-violation? ex)
+ (print-ex ex)
+ (reset k)]
+ [(interrupted-condition? ex)
+ (flush-output-port (console-output-port))
+ (newline (console-output-port))
+ ...

Applied Derick's patch in revision 1569. Thanks to the both of you.