core: avoid writing objects.cache if set to /dev/null

refs #3819

Changelog

@@ -24,6 +24,7 @@ ENHANCEMENTS
 * core: enhance illegal macro character processing performance (Andreas Ericsson) #3389 - MF
 * core: add the notification type by string to debug logs; set CUSTOM=8, STALKING=9 (Andreas Ericsson) #3818 - MF
 * core: skip writing status.dat if explicitely set to /dev/null (e.g. when using alternate data retrieval methods like IDOUtils) (Andreas Ericsson) #3819 - MF
+* core: avoid writing objects.cache if set to /dev/null (Andreas Ericsson) #3819 - MF
 
 * classic ui: Add "set_expire_ack_by_default" to cgi configuration #3476 - CF
 * classic ui: Add "send_ack_notifications" to cgi configuration (TheCry) #3467 - CF
@@ -87,6 +88,7 @@ CHANGES
 
 * icinga.cfg - enable_state_based_escalation_ranges=0 (disabled if not set) fix for #3441
 * icinga.cfg - set status_file=/dev/null to disable its creation #3819
+* icinga.cfg - set object_cache_file=/dev/null to disable its creation #3819
 
 * core: -v param can be used more than once #3510
 * core: 'Warning: Host ... has no service associated with it!' now happens only in icinga -vv icinga.cfg #3510

sample-config/icinga.cfg.in

@@ -71,6 +71,10 @@ cfg_dir=@sysconfdir@/modules
 # this cache file (rather than looking at the object config files
 # directly) in order to prevent inconsistencies that can occur
 # when the config files are modified after Icinga starts.
+# If you explicitely set it to /dev/null the core will skip writing
+# the objects cache file entirely.
+# Tip: Use that file to debug your configuration with fully resolved
+# objects like the core sees them.
 
 object_cache_file=@STATEDIR@/objects.cache
 

xdata/xodtemplate.c

@@ -10489,6 +10489,9 @@ int xodtemplate_cache_objects(char *cache_file) {
 	time_t current_time = 0L;
 	void *ptr = NULL;
 
+	/* skip if set to /dev/null */
+	if (!cache_file || !strcmp(cache_file, "/dev/null"))
+		return OK;
 
 	time(&current_time);