Merge pull request #6838 from oranagra/rm_scan_dict_rehash

RM_Scan disable dict rehashing

2 files changed, 21 insertions, 6 deletions

diff --git a/src/dict.c b/src/dict.c
index 106467ef7..93e6c39a7 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -871,6 +871,10 @@ unsigned long dictScan(dict *d,
 
     if (dictSize(d) == 0) return 0;
 
+    /* Having a safe iterator means no rehashing can happen, see _dictRehashStep.
+     * This is needed in case the scan callback tries to do dictFind or alike. */
+    d->iterators++;
+
     if (!dictIsRehashing(d)) {
         t0 = &(d->ht[0]);
         m0 = t0->sizemask;
@@ -937,6 +941,9 @@ unsigned long dictScan(dict *d,
         } while (v & (m0 ^ m1));
     }
 
+    /* undo the ++ at the top */
+    d->iterators--;
+
     return v;
 }
 
diff --git a/src/module.c b/src/module.c
index b00118681..b821f0c31 100644
--- a/src/module.c
+++ b/src/module.c
@@ -6553,9 +6553,13 @@ void RM_ScanCursorDestroy(RedisModuleScanCursor *cursor) {
  *      }
  *      RedisModule_ScanCursorDestroy(c);
  *
- *  The function will return 1 if there are more elements to scan and 0 otherwise,
- *  possibly setting errno if the call failed.
- *  It is also possible to restart and existing cursor using RM_CursorRestart. */
+ * The function will return 1 if there are more elements to scan and 0 otherwise,
+ * possibly setting errno if the call failed.
+ * It is also possible to restart and existing cursor using RM_CursorRestart.
+ *
+ * NOTE: You must avoid doing any database changes from within the callback, you should avoid any
+ * RedisModule_OpenKey or RedisModule_Call, if you need to do these, you need to keep the key name
+ * and do any work you need to do after the call to Scan returns. */
 int RM_Scan(RedisModuleCtx *ctx, RedisModuleScanCursor *cursor, RedisModuleScanCB fn, void *privdata) {
     if (cursor->done) {
         errno = ENOENT;
@@ -6633,9 +6637,13 @@ static void moduleScanKeyCallback(void *privdata, const dictEntry *de) {
  *      RedisModule_CloseKey(key);
  *      RedisModule_ScanCursorDestroy(c);
  *
- *  The function will return 1 if there are more elements to scan and 0 otherwise,
- *  possibly setting errno if the call failed.
- *  It is also possible to restart and existing cursor using RM_CursorRestart. */
+ * The function will return 1 if there are more elements to scan and 0 otherwise,
+ * possibly setting errno if the call failed.
+ * It is also possible to restart and existing cursor using RM_CursorRestart.
+ *
+ * NOTE: You must avoid doing any database changes from within the callback, you should avoid any
+ * RedisModule_OpenKey or RedisModule_Call, if you need to do these, you need to keep the field name
+ * and do any work you need to do after the call to Scan returns. */
 int RM_ScanKey(RedisModuleKey *key, RedisModuleScanCursor *cursor, RedisModuleScanKeyCB fn, void *privdata) {
     if (key == NULL || key->value == NULL) {
         errno = EINVAL;