Module API to allow writes after key space notification hooks (#11199)

### Summary of API additions

* `RedisModule_AddPostNotificationJob` - new API to call inside a key space
  notification (and on more locations in the future) and allow to add a post job as describe above.
* New module option, `REDISMODULE_OPTIONS_ALLOW_NESTED_KEYSPACE_NOTIFICATIONS`,
  allows to disable Redis protection of nested key-space notifications.
* `RedisModule_GetModuleOptionsAll` - gets the mask of all supported module options so a module
  will be able to check if a given option is supported by the current running Redis instance.

### Background

The following PR is a proposal of handling write operations inside module key space notifications.
After a lot of discussions we came to a conclusion that module should not perform any write
operations on key space notification.

Some examples of issues that such write operation can cause are describe on the following links:

* Bad replication oreder - https://github.com/redis/redis/pull/10969
* Used after free - https://github.com/redis/redis/pull/10969#issuecomment-1223771006
* Used after free - https://github.com/redis/redis/pull/9406#issuecomment-1221684054

There are probably more issues that are yet to be discovered. The underline problem with writing
inside key space notification is that the notification runs synchronously, this means that the notification
code will be executed in the middle on Redis logic (commands logic, eviction, expire).
Redis **do not assume** that the data might change while running the logic and such changes
can crash Redis or cause unexpected behaviour.

The solution is to state that modules **should not** perform any write command inside key space
notification (we can chose whether or not we want to force it). To still cover the use-case where
module wants to perform a write operation as a reaction to key space notifications, we introduce
a new API , `RedisModule_AddPostNotificationJob`, that allows to register a callback that will be
called by Redis when the following conditions hold:

* It is safe to perform any write operation.
* The job will be called atomically along side the operation that triggers it (in our case, key
  space notification).

Module can use this new API to safely perform any write operation and still achieve atomicity
between the notification and the write.

Although currently the API is supported on key space notifications, the API is written in a generic
way so that in the future we will be able to use it on other places (server events for example).

### Technical Details

Whenever a module uses `RedisModule_AddPostNotificationJob` the callback is added to a list
of callbacks (called `modulePostExecUnitJobs`) that need to be invoke after the current execution
unit ends (whether its a command, eviction, or active expire). In order to trigger those callback
atomically with the notification effect, we call those callbacks on `postExecutionUnitOperations`
(which was `propagatePendingCommands` before this PR). The new function fires the post jobs
and then calls `propagatePendingCommands`.

If the callback perform more operations that triggers more key space notifications. Those keys
space notifications might register more callbacks. Those callbacks will be added to the end
of `modulePostExecUnitJobs` list and will be invoke atomically after the current callback ends.
This raises a concerns of entering an infinite loops, we consider infinite loops as a logical bug
that need to be fixed in the module, an attempt to protect against infinite loops by halting the
execution could result in violation of the feature correctness and so **Redis will make no attempt
to protect the module from infinite loops**

In addition, currently key space notifications are not nested. Some modules might want to allow
nesting key-space notifications. To allow that and keep backward compatibility, we introduce a
new module option called `REDISMODULE_OPTIONS_ALLOW_NESTED_KEYSPACE_NOTIFICATIONS`.
Setting this option will disable the Redis key-space notifications nesting protection and will
pass this responsibility to the module.

### Redis infrastructure

This PR promotes the existing `propagatePendingCommands` to an "Execution Unit" concept,
which is called after each atomic unit of execution,

Co-authored-by: Oran Agra <oran@redislabs.com>
Co-authored-by: Yossi Gottlieb <yossigo@gmail.com>
Co-authored-by: Madelyn Olson <34459052+madolson@users.noreply.github.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/server.h b/src/server.h
index 0faf80c0f..3c2a6a045 100644
--- a/src/server.h
+++ b/src/server.h
@@ -2424,6 +2424,7 @@ void moduleAcquireGIL(void);
 int moduleTryAcquireGIL(void);
 void moduleReleaseGIL(void);
 void moduleNotifyKeyspaceEvent(int type, const char *event, robj *key, int dbid);
+void firePostExecutionUnitJobs();
 void moduleCallCommandFilters(client *c);
 void ModuleForkDoneHandler(int exitcode, int bysignal);
 int TerminateModuleForkChild(int child_pid, int wait);
@@ -2946,7 +2947,7 @@ void startCommandExecution();
 int incrCommandStatsOnError(struct redisCommand *cmd, int flags);
 void call(client *c, int flags);
 void alsoPropagate(int dbid, robj **argv, int argc, int target);
-void propagatePendingCommands();
+void postExecutionUnitOperations();
 void redisOpArrayFree(redisOpArray *oa);
 void forceCommandPropagation(client *c, int flags);
 void preventCommandPropagation(client *c);