fsmonitor: optimize processing of directory events

Teach Git to perform binary search over the cache-entries for a directory
notification and then linearly scan forward to find the immediate children.

Previously, when the FSMonitor reported a modified directory Git would
perform a linear search on the entire cache-entry array for all
entries matching that directory prefix and invalidate them.  Since the
cache-entry array is already sorted, we can use a binary search to
find the first matching entry and then only linearly walk forward and
invalidate entries until the prefix changes.

Also, the original code would invalidate anything having the same
directory prefix.  Since a directory event should only be received for
items that are immediately within the directory (and not within
sub-directories of it), only invalidate those entries and not the
whole subtree.

Signed-off-by: Jeff Hostetler <[email protected]>

Author: jeffhostetler

fsmonitor.c

@@ -199,25 +199,24 @@ static void fsmonitor_refresh_callback(struct index_state *istate, char *name)
 {
 	int i, len = strlen(name);
 	if (name[len - 1] == '/') {
-
-		/*
-		 * TODO We should binary search to find the first path with
-		 * TODO this directory prefix.  Then linearly update entries
-		 * TODO while the prefix matches.  Taking care to search without
-		 * TODO the trailing slash -- because '/' sorts after a few
-		 * TODO interesting special chars, like '.' and ' '.
-		 */
+		const char *rel;
+		int pos = index_name_pos(istate, name, len);
+		if (pos < 0)
+			pos = -pos - 1;
 
 		/* Mark all entries for the folder invalid */
-		for (i = 0; i < istate->cache_nr; i++) {
-			if (istate->cache[i]->ce_flags & CE_FSMONITOR_VALID &&
-			    starts_with(istate->cache[i]->name, name))
+		for (i = pos; i < istate->cache_nr; i++) {
+			if (!starts_with(istate->cache[i]->name, name))
+				break;
+			/* Only mark the immediate children in the folder */
+			rel = istate->cache[i]->name + len;
+			if (!strchr(rel, '/'))
 				istate->cache[i]->ce_flags &= ~CE_FSMONITOR_VALID;
 		}
 		/* Need to remove the / from the path for the untracked cache */
 		name[len - 1] = '\0';
 	} else {
-		int pos = index_name_pos(istate, name, strlen(name));
+		int pos = index_name_pos(istate, name, len);
 
 		if (pos >= 0) {
 			struct cache_entry *ce = istate->cache[pos];