Subject: Re: bug#10664: 24.0.93; JIT font-lock infloops in a C file

From: Eli Zaretskii <[email-masked]>
Date: Wed, 08 Feb 2012 19:49:58 +0200

> Date: Wed, 8 Feb 2012 11:47:49 +0000
> Cc: Eli Zaretskii <[email-masked]>, [email-masked]
> From: Alan Mackenzie <[email-masked]>
> 
> #########################################################################
> 1 template <typename T>
> 2
> 3
> 4 void myfunc(T* p) {}
> #########################################################################
> 
> This is fontified correctly.  Type a space on L2.  This is OK for half a
> second, then context fontification messes up L4.  The correct
> fontification can only be restored by a change to L4.
> 
> Revision #106729 fixes this problem, after a space on L2, by making the
> fontification start at L1 rather than L2.
> 
> The exact mechanism of why the problem happened is buried in my log, and
> I could dredge it up if you're really interested.
> 
> The problem with this approach is demonstrated in Eli's socket.c:
> 
> SCM_DEFINE (scm_inet_pton, "inet-pton", 2, 0, 0,
>             (SCM family, SCM address),
>             "Convert a string containing a printable network address to\n"
>             "an integer address.  Note that unlike the C version of this\n"
>             "function,\n"
>             "the result is an integer with normal host byte ordering.\n"
>             "@var{family} can be @code{AF_INET} or @code{AF_INET6}.  E.g.,\n\n"
>             "@lisp\n"
>             "(inet-pton AF_INET \"127.0.0.1\") @result{} 2130706433\n"
>             "(inet-pton AF_INET6 \"::1\") @result{} 1\n"
>             "@end lisp")
> #define FUNC_NAME s_scm_inet_pton
> {
> 
> A 500 byte chunk of fontification ends just before "@end lisp".  For
> this line, the start of the next chunk is "pushed back" to the
> SCM_DEFINE line to get a proper context for "@end lisp".  It then
> repeatedly fontifies the same chunk.
> 
> Interestingly, EOL just before "@end lisp" is exactly 500 bytes after
> the initial scm_inet_pton.

Thanks for explaining this.

Would it fix the problem if, when jit-lock is "pushed back" by N >= 500
characters, it will fontify N + n characters, where n > 0 ?  (E.g., set
n = 100.)