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Re: [Bug-readline] documentation of signal handling

From: Chet Ramey
Subject: Re: [Bug-readline] documentation of signal handling
Date: Thu, 28 Apr 2016 15:36:43 -0400
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:45.0) Gecko/20100101 Thunderbird/45.0

On 4/26/16 2:54 PM, address@hidden wrote:

> I have a short example program that I attached. I haven't added
> SIGWINCH handling yet. You can see that I use siglongjmp to get out of
> the SIGINT handler - a tip I found on stackoverflow - and then I try a
> few miscellaneous Readline cleanup functions. I'm trying to get
> behavior like Bash - ^C should cancel anything I've entered on a line,
> an give me a new prompt. (I notice that GDB has different, somewhat
> annoying behavior, of keeping the input line on ^C)
> The example that I wrote has a bug which both R and Python suffer
> from. The problematic behavior is that when the user hits ^C during a
> reverse-isearch, the last isearch proposal is kept as a "hidden" input.
> For R, I reported this bug in
> <https://bugs.r-project.org/bugzilla/show_bug.cgi?id=16603>.
> I'm a bit curious to know if this bug has always been present, or if
> it appeared with Readline 6.3 or some other recent version.

It's always been present.

You can fix your problem in readline-6.3 and earlier by making your code
look like this:

    if(sigsetjmp(env, 1)) {
        rl_free_line_state ();
        rl_cleanup_after_signal ();

        rl_done = 1;
        rl_callback_handler_remove ();

If you want a little more control, you can replace rl_done = 1 with

rl_line_buffer[rl_point = rl_end = rl_mark = 0] = 0;

That part clears out the line buffer.  The call to UNSETSTATE cleans up the
readline state it uses to keep track of where it is between calls to
rl_callback_read_char().  Without that, readline's state tells it it's
still in the middle of the incremental search.

#ifdef to taste if some of the RL_STATE values aren't defined in the
readline version you're interested in.

Bash is not a good example to look at for this code, since it doesn't use
the callback interface.

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/

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