Dictionaries with reference counters and full deletion support during traversal (#13195)

* dont use atomic operations when not needed; detect misuse of the the unsafe functions

* use relaxed atomic operations for statistics

* use relaxed atomic operations for statistics

* dictionaries now use reference counters, allowing deletetions of any item while traversing it

* added acquire/release interface to dictionaries

* added unittest for reference counters

* added NETDATA_INTERNAL_CHECKS logs to detect non-exclusive access to crusial parts of the dictionaries

* dictionaries cannot be deleted while there are referenced items in them - they will be deleted once the last item gets unreferenced

* cleanup

* properly cleanup released items

* maintain counters for readers and writers; defer all deletes on sorted walkthrough; cleaner internal_error();

* somewhat faster reference counters on single threaded dictionaries

* minor optimizations; allow compiling without internal checks

1 files changed, 9 insertions, 14 deletions

diff --git a/database/rrdlabels.c b/database/rrdlabels.c
index 7032df70d4..4a610b1587 100644
--- a/database/rrdlabels.c
+++ b/database/rrdlabels.c
@@ -611,20 +611,15 @@ void rrdlabels_add_pair(DICTIONARY *dict, const char *string, RRDLABEL_SRC ls) {
 // rrdlabels_get_to_buffer_or_null()
 
 void rrdlabels_get_value_to_buffer_or_null(DICTIONARY *labels, BUFFER *wb, const char *key, const char *quote, const char *null) {
-    // Get a read lock on the dictionary
-    // to copy the value into the buffer
-    void *v;
-    dfe_start_read(labels, v) {
-        RRDLABEL *lb = dictionary_get_having_read_lock(labels, key);
-
-        if(lb && lb->value)
-            buffer_sprintf(wb, "%s%s%s", quote, lb->value, quote);
-        else
-            buffer_strcat(wb, null);
-
-        break;
-    }
-    dfe_done(v);
+    void *acquired_item = dictionary_acquire_item(labels, key);
+    RRDLABEL *lb = dictionary_acquired_item_value(labels, acquired_item);
+
+    if(lb && lb->value)
+        buffer_sprintf(wb, "%s%s%s", quote, lb->value, quote);
+    else
+        buffer_strcat(wb, null);
+
+    dictionary_acquired_item_release(labels, acquired_item);
 }