[td-1569]

src/util/src/tcache.c

@@ -335,7 +335,7 @@ void *taosCacheTransfer(SCacheObj *pCacheObj, void **data) {
 }
 
 void taosCacheRelease(SCacheObj *pCacheObj, void **data, bool _remove) {
-  if (pCacheObj == NULL || taosHashGetSize(pCacheObj->pHashTable) + pCacheObj->numOfElemsInTrash == 0) {
+  if (pCacheObj == NULL) {
     return;
   }
 
@@ -344,6 +344,11 @@ void taosCacheRelease(SCacheObj *pCacheObj, void **data, bool _remove) {
     return;
   }
 
+
+  // The operation of removal from hash table and addition to trashcan is not an atomic operation,
+  // therefore the check for the empty of both the hash table and the trashcan has a race condition.
+  // It happens when there is only one object in the cache, and two threads which has referenced this object
+  // start to free the it simultaneously. [TD-1569]
   size_t offset = offsetof(SCacheDataNode, data);
   
   SCacheDataNode *pNode = (SCacheDataNode *)((char *)(*data) - offset);