Add a special notification unlink available only for modules (#9406)

Add a new module event `RedisModule_Event_Key`, this event is fired
when a key is removed from the keyspace.
The event includes an open key that can be used for reading the key before
it is removed. Modules can also extract the key-name, and use RM_Open
or RM_Call to access key from within that event, but shouldn't modify anything
from within this event.

The following sub events are available:
  - `REDISMODULE_SUBEVENT_KEY_DELETED`
  - `REDISMODULE_SUBEVENT_KEY_EXPIRED`
  - `REDISMODULE_SUBEVENT_KEY_EVICTED`
  - `REDISMODULE_SUBEVENT_KEY_OVERWRITE`

The data pointer can be casted to a RedisModuleKeyInfo structure
with the following fields:
```
     RedisModuleKey *key;    // Opened Key
 ```

### internals

* We also add two dict functions:
  `dictTwoPhaseUnlinkFind` finds an element from the table, also get the plink of the entry.
  The entry is returned if the element is found. The user should later call `dictTwoPhaseUnlinkFree`
  with it in order to unlink and release it. Otherwise if the key is not found, NULL is returned.
  These two functions should be used in pair. `dictTwoPhaseUnlinkFind` pauses rehash and
  `dictTwoPhaseUnlinkFree` resumes rehash.
* We change `dbOverwrite` to `dbReplaceValue` which just replaces the value of the key and
  doesn't fire any events. The "overwrite" part (which emits events) is just when called from `setKey`,
  the other places that called dbOverwrite were ones that just update the value in-place (INCR*, SPOP,
  and dbUnshareStringValue). This should not have any real impact since `moduleNotifyKeyUnlink` and
  `signalDeletedKeyAsReady` wouldn't have mattered in these cases anyway (i.e. module keys and
  stream keys didn't have direct calls to dbOverwrite)
* since we allow doing RM_OpenKey from withing these callbacks, we temporarily disable lazy expiry.
* We also temporarily disable lazy expiry when we are in unlink/unlink2 callback and keyspace 
  notification callback.
* Move special definitions to the top of redismodule.h
  This is needed to resolve compilation errors with RedisModuleKeyInfoV1
  that carries a RedisModuleKey member.

Co-authored-by: Oran Agra <oran@redislabs.com>

1 files changed, 44 insertions, 19 deletions

diff --git a/src/redismodule.h b/src/redismodule.h
index 7f04f7ba4..d65687a23 100644
--- a/src/redismodule.h
+++ b/src/redismodule.h
@@ -6,6 +6,28 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+
+typedef struct RedisModuleString RedisModuleString;
+typedef struct RedisModuleKey RedisModuleKey;
+
+/* -------------- Defines NOT common between core and modules ------------- */
+
+#if defined REDISMODULE_CORE
+/* Things only defined for the modules core (server), not exported to modules
+ * that include this file. */
+
+#define RedisModuleString robj
+
+#endif /* defined REDISMODULE_CORE */
+
+#if !defined REDISMODULE_CORE && !defined REDISMODULE_CORE_MODULE
+/* Things defined for modules, but not for core-modules. */
+
+typedef long long mstime_t;
+typedef long long ustime_t;
+
+#endif /* !defined REDISMODULE_CORE && !defined REDISMODULE_CORE_MODULE */
+
 /* ---------------- Defines common between core and modules --------------- */
 
 /* Error status return values. */
@@ -458,7 +480,8 @@ typedef void (*RedisModuleEventLoopOneShotFunc)(void *user_data);
 #define REDISMODULE_EVENT_REPL_ASYNC_LOAD 14
 #define REDISMODULE_EVENT_EVENTLOOP 15
 #define REDISMODULE_EVENT_CONFIG 16
-#define _REDISMODULE_EVENT_NEXT 17 /* Next event flag, should be updated if a new event added. */
+#define REDISMODULE_EVENT_KEY 17
+#define _REDISMODULE_EVENT_NEXT 18 /* Next event flag, should be updated if a new event added. */
 
 typedef struct RedisModuleEvent {
     uint64_t id;        /* REDISMODULE_EVENT_... defines. */
@@ -565,6 +588,10 @@ static const RedisModuleEvent
     RedisModuleEvent_Config = {
         REDISMODULE_EVENT_CONFIG,
         1
+    },
+    RedisModuleEvent_Key = {
+        REDISMODULE_EVENT_KEY,
+        1
     };
 
 /* Those are values that are used for the 'subevent' callback argument. */
@@ -633,6 +660,12 @@ static const RedisModuleEvent
 #define REDISMODULE_SUBEVENT_EVENTLOOP_AFTER_SLEEP 1
 #define _REDISMODULE_SUBEVENT_EVENTLOOP_NEXT 2
 
+#define REDISMODULE_SUBEVENT_KEY_DELETED 0
+#define REDISMODULE_SUBEVENT_KEY_EXPIRED 1
+#define REDISMODULE_SUBEVENT_KEY_EVICTED 2
+#define REDISMODULE_SUBEVENT_KEY_OVERWRITTEN 3
+#define _REDISMODULE_SUBEVENT_KEY_NEXT 4
+
 #define _REDISMODULE_SUBEVENT_SHUTDOWN_NEXT 0
 #define _REDISMODULE_SUBEVENT_CRON_LOOP_NEXT 0
 #define _REDISMODULE_SUBEVENT_SWAPDB_NEXT 0
@@ -756,6 +789,16 @@ typedef struct RedisModuleSwapDbInfo {
 
 #define RedisModuleSwapDbInfo RedisModuleSwapDbInfoV1
 
+#define REDISMODULE_KEYINFO_VERSION 1
+typedef struct RedisModuleKeyInfo {
+    uint64_t version;       /* Not used since this structure is never passed
+                               from the module to the core right now. Here
+                               for future compatibility. */
+    RedisModuleKey *key;    /* Opened key. */
+} RedisModuleKeyInfoV1;
+
+#define RedisModuleKeyInfo RedisModuleKeyInfoV1
+
 typedef enum {
     REDISMODULE_ACL_LOG_AUTH = 0, /* Authentication failure */
     REDISMODULE_ACL_LOG_CMD, /* Command authorization failure */
@@ -764,7 +807,6 @@ typedef enum {
 } RedisModuleACLLogEntryReason;
 
 /* Incomplete structures needed by both the core and modules. */
-typedef struct RedisModuleString RedisModuleString;
 typedef struct RedisModuleIO RedisModuleIO;
 typedef struct RedisModuleDigest RedisModuleDigest;
 typedef struct RedisModuleInfoCtx RedisModuleInfoCtx;
@@ -778,22 +820,6 @@ typedef void (*RedisModuleUserChangedFunc) (uint64_t client_id, void *privdata);
 
 /* ------------------------- End of common defines ------------------------ */
 
-#if defined REDISMODULE_CORE
-/* Things only defined for the modules core (server), not exported to modules
- * that include this file. */
-
-#define RedisModuleString robj
-
-#endif /* defined REDISMODULE_CORE */
-
-#if !defined REDISMODULE_CORE && !defined REDISMODULE_CORE_MODULE
-/* Things defined for modules, but not for core-modules. */
-
-typedef long long mstime_t;
-typedef long long ustime_t;
-
-#endif /* !defined REDISMODULE_CORE && !defined REDISMODULE_CORE_MODULE */
-
 /* ----------- The rest of the defines are only for modules ----------------- */
 #if !defined REDISMODULE_CORE || defined REDISMODULE_CORE_MODULE
 /* Things defined for modules and core-modules. */
@@ -826,7 +852,6 @@ typedef long long ustime_t;
 /* Incomplete structures for compiler checks but opaque access. */
 typedef struct RedisModuleCtx RedisModuleCtx;
 typedef struct RedisModuleCommand RedisModuleCommand;
-typedef struct RedisModuleKey RedisModuleKey;
 typedef struct RedisModuleCallReply RedisModuleCallReply;
 typedef struct RedisModuleType RedisModuleType;
 typedef struct RedisModuleBlockedClient RedisModuleBlockedClient;