regular expression matching can now be reliably interrupted using CTRL+CHEADmaster-fmsbw-cimaster

* The previous checks for interruptions only helped in a few corner cases
  like for very high search-repeat counts or during backwards searches across
  the entire buffer.
* But even with terex' more predictable runtime properties
  a single regex execution can hang quite a long time.
  E.g. `S^EM^X$` on a huge buffer or even more so with backreferences as in
  `S^~(.*)\1$`.
* We now use the new tere_set_is_interrupted_cb() to register
  teco_interface_is_interrupted(). Types should be compatible as long
  as gboolean resolves to int.
* It's no longer necessary to manually check for teco_interface_is_interrupted()
  since tere_exec() now returns REG_EINTR in case the callback returned TRUE
  in which case it's handled by teco_error_regex_set().

3 files changed, 7 insertions, 22 deletions

diff --git a/TODO b/TODO
index b2de61c..ec65898 100644
--- a/TODO
+++ b/TODO
@@ -74,12 +74,6 @@ Known Bugs:
    and b) the file mode and ownership of re-created files can be preserved.
    We should fall back silently to an (inefficient) memory copy or temporary
    file strategy if this is detected.
- * It is still possible to hang searches on huge files since a single match
-   could still scan too much memory - e.g. try searching for a word that
-   occurs only at the end of the huge file.
-   Can probably be avoided by including `(*MATCH_LIMIT=d)` in the pattern.
-   A new regexp engine should also allow interruptions within a single match,
-   so we don't have to invent limits like that.
  * It is still possible to crash SciTECO using recursive functions,
    since they map to the C program's call stack.
    It is perhaps best to use another stack of
diff --git a/contrib/terex b/contrib/terex
-Subproject fa3d463a4cd563f3c5f29331f48a0161bf58686
+Subproject d71d7527a8be8654560867d761036598408bfe1
diff --git a/src/search.c b/src/search.c
index 491ddbb..1ab925c 100644
--- a/src/search.c
+++ b/src/search.c
@@ -708,14 +708,6 @@ teco_do_search_forward(regex_t *re, gsize from, gsize to, gint *count, GError **
 	                       1+re->re_nsub, info, eflags)) == REG_OKAY && --(*count)) {
 		buffer += info[0].rm_eo;
 		from += info[0].rm_eo;
-
-		/*
-		 * FIXME: A single pathological match could already be excessively slow.
-		 */
-		if (G_UNLIKELY(teco_interface_is_interrupted())) {
-			teco_error_interrupted_set(error);
-			return FALSE;
-		}
 	}
 
 	if (rc == REG_OKAY) {
@@ -810,14 +802,6 @@ teco_do_search_backwards(regex_t *re, gsize from, gsize to, gint *count, GError
 		gint rc;
 
 		for (;;) {
-			/*
-			 * FIXME: A single pathological match could already be excessively slow.
-			 */
-			if (G_UNLIKELY(teco_interface_is_interrupted())) {
-				teco_error_interrupted_set(error);
-				return FALSE;
-			}
-
 			rc = tere_exec(re, (const chr *)buffer+from_block+offset, to_block-from_block-offset,
 			               &details, 1+re->re_nsub, info, eflags);
 			if (rc != REG_OKAY)
@@ -1000,6 +984,13 @@ teco_state_search_process(teco_machine_main_t *ctx, teco_string_t str, gsize new
 	if (rc != REG_OKAY)
 		goto failure;
 
+	/*
+	 * Check for interruptions during matching since they can be quite slow
+	 * especially when matching with regular expressions and backreferences
+	 * (e.g. @S/^~(.*)\1/).
+	 */
+	tere_set_is_interrupted_cb(&re, teco_interface_is_interrupted);
+
 	if (!teco_qreg_current &&
 	    teco_ring_current != teco_search_parameters.from_buffer) {
 		teco_ring_undo_edit();