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FOR_EACH_TAIL now checks for quit

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As per Eli Zaretskii (Bug#25606#20).  Although these calls to
maybe_quit are unnecessary in practice, Eli was not convinced
that the calls are unnecessary.
* src/lisp.h (FOR_EACH_TAIL, FOR_EACH_TAIL_CONS):
Call maybe_quit every so often.
(FOR_EACH_TAIL_INTERNAL): New arg CHECK_QUIT.  All callers changed.
This commit is contained in:
Paul Eggert 2017-02-05 13:25:37 -08:00 committed by Paul Eggert
parent 14dd9101ec
commit b491322ed0
1 changed files with 32 additions and 20 deletions
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52
src/lisp.h
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@ -4580,44 +4580,56 @@ enum
Lisp_String)) \
: make_unibyte_string (str, len))
/* Loop over tails of LIST, checking for dotted lists and cycles.
/* Loop over tails of LIST, checking for dotted lists and cycles,
and possibly quitting after each loop iteration.
In the loop body, ‘li.tail’ is the current cons; the name ‘li’ is
short for “list iterator”. The expression LIST may be evaluated
more than once, and so should not have side effects. The loop body
should not modify the list’s top level structure other than by
perhaps deleting the current cons.
Use Brent’s teleporting tortoise-hare algorithm. See:
Brent RP. BIT. 1980;20(2):176-84. doi:10.1007/BF01933190
http://maths-people.anu.edu.au/~brent/pd/rpb051i.pdf */
perhaps deleting the current cons. */
#define FOR_EACH_TAIL(list) \
FOR_EACH_TAIL_INTERNAL (list, CHECK_LIST_END (li.tail, list), \
circular_list (list))
circular_list (list), true)
/* Like FOR_EACH_TAIL (LIST), except check only for cycles. */
/* Like FOR_EACH_TAIL (LIST), except do not check for dotted lists. */
#define FOR_EACH_TAIL_CONS(list) \
FOR_EACH_TAIL_INTERNAL (list, (void) 0, circular_list (list))
#define FOR_EACH_TAIL_CONS(list) \
FOR_EACH_TAIL_INTERNAL (list, (void) 0, circular_list (list), true)
/* Like FOR_EACH_TAIL (LIST), except check for neither dotted lists
nor cycles. */
nor cycles, and do not quit. */
#define FOR_EACH_TAIL_SAFE(list) \
FOR_EACH_TAIL_INTERNAL (list, (void) 0, (void) (li.tail = Qnil))
FOR_EACH_TAIL_INTERNAL (list, (void) 0, (void) (li.tail = Qnil), false)
/* Like FOR_EACH_TAIL (LIST), except evaluate DOTTED or CYCLE,
respectively, if a dotted list or cycle is found. This is an
internal macro intended for use only by the above macros. */
respectively, if a dotted list or cycle is found, and check for
quit if CHECK_QUIT. This is an internal macro intended for use
only by the above macros.
#define FOR_EACH_TAIL_INTERNAL(list, dotted, cycle) \
for (struct { Lisp_Object tail, tortoise; intptr_t n, max; } li \
= { list, list, 2, 2 }; \
Use Brent’s teleporting tortoise-hare algorithm. See:
Brent RP. BIT. 1980;20(2):176-84. doi:10.1007/BF01933190
http://maths-people.anu.edu.au/~brent/pd/rpb051i.pdf
This macro uses maybe_quit because of an excess of caution. The
call to maybe_quit should not be needed in practice, as a very long
list, whether circular or not, will cause Emacs to be so slow in
other noninterruptible areas (e.g., garbage collection) that there
is little point to calling maybe_quit here. */
#define FOR_EACH_TAIL_INTERNAL(list, dotted, cycle, check_quit) \
for (struct { Lisp_Object tail, tortoise; intptr_t max, n; \
unsigned short int q; \
} li = { list, list, 2, 0, 2 }; \
CONSP (li.tail) || (dotted, false); \
(li.tail = XCDR (li.tail), \
(li.n-- == 0 \
? (void) (li.n = li.max <<= 1, li.tortoise = li.tail) \
: EQ (li.tail, li.tortoise) ? (cycle) : (void) 0)))
((--li.q != 0 \
|| ((check_quit) ? maybe_quit () : (void) 0, 0 < --li.n) \
|| (li.q = li.n = li.max <<= 1, li.n >>= USHRT_WIDTH, \
li.tortoise = li.tail, false)) \
&& EQ (li.tail, li.tortoise)) \
? (cycle) : (void) 0))
/* Do a `for' loop over alist values. */