Faster rrdcontext (#13629)

* moved rrdcontexts processing to worker thread

* added loggings

* check for aclk deeper in the code

* removed unessesary logs

* code re-organization; cleanup; more comments; better error handling; rrdcontext locks optimization; more clarity

* updated 2 comments

* make instances walkthrough reentrant; move context lock to the place is really needed

* created macro for reentrant dictionary walkthrough

* incremental updates on instances and metrics

* renamed family of rrdcontext workers

* prevent crash in case RRDINSTANCE or RRDMETRIC is freed during shutdown

* prevent crash during rrddim save, on out of memory fatal()

* always post-process contexts

* added tracing for tracking the caller that trigger updates

* more details on tracing info

* fix for charts that are collected without metrics

2 files changed, 11 insertions, 1 deletions

diff --git a/libnetdata/dictionary/dictionary.c b/libnetdata/dictionary/dictionary.c
index 6e37554ea4..4af2c391a3 100644
--- a/libnetdata/dictionary/dictionary.c
+++ b/libnetdata/dictionary/dictionary.c
@@ -121,30 +121,39 @@ void dictionary_register_react_callback(DICTIONARY *dict, void (*react_callback)
 // dictionary statistics maintenance
 
 long int dictionary_stats_allocated_memory(DICTIONARY *dict) {
+    if(unlikely(!dict)) return 0;
     return dict->memory;
 }
 long int dictionary_stats_entries(DICTIONARY *dict) {
+    if(unlikely(!dict)) return 0;
     return dict->entries;
 }
 size_t dictionary_stats_version(DICTIONARY *dict) {
+    if(unlikely(!dict)) return 0;
     return dict->version;
 }
 size_t dictionary_stats_searches(DICTIONARY *dict) {
+    if(unlikely(!dict)) return 0;
     return dict->searches;
 }
 size_t dictionary_stats_inserts(DICTIONARY *dict) {
+    if(unlikely(!dict)) return 0;
     return dict->inserts;
 }
 size_t dictionary_stats_deletes(DICTIONARY *dict) {
+    if(unlikely(!dict)) return 0;
     return dict->deletes;
 }
 size_t dictionary_stats_resets(DICTIONARY *dict) {
+    if(unlikely(!dict)) return 0;
     return dict->resets;
 }
 size_t dictionary_stats_walkthroughs(DICTIONARY *dict) {
+    if(unlikely(!dict)) return 0;
     return dict->walkthroughs;
 }
 size_t dictionary_stats_referenced_items(DICTIONARY *dict) {
+    if(unlikely(!dict)) return 0;
     return __atomic_load_n(&dict->referenced_items, __ATOMIC_SEQ_CST);
 }
 
diff --git a/libnetdata/dictionary/dictionary.h b/libnetdata/dictionary/dictionary.h
index 9c2ea72e41..3cda4baf8e 100644
--- a/libnetdata/dictionary/dictionary.h
+++ b/libnetdata/dictionary/dictionary.h
@@ -198,10 +198,11 @@ typedef DICTFE_CONST struct dictionary_foreach {
 
 #define dfe_start_read(dict, value) dfe_start_rw(dict, value, DICTIONARY_LOCK_READ)
 #define dfe_start_write(dict, value) dfe_start_rw(dict, value, DICTIONARY_LOCK_WRITE)
+#define dfe_start_reentrant(dict, value) dfe_start_rw(dict, value, DICTIONARY_LOCK_REENTRANT)
 #define dfe_start_rw(dict, value, mode) \
         do { \
             DICTFE value ## _dfe = {};  \
-            const char *value ## _name; (void)(value ## _name); (void)value; \
+            const char *value ## _name; (void)(value ## _name); (void)(value); \
             for((value) = dictionary_foreach_start_rw(&value ## _dfe, (dict), (mode)), ( value ## _name ) = value ## _dfe.name; \
                 (value ## _dfe.name) ;\
                 (value) = dictionary_foreach_next(&value ## _dfe), ( value ## _name ) = value ## _dfe.name) \