Unified MULTI, LUA, and RM_Call with respect to blocking commands (#8025)
Blocking command should not be used with MULTI, LUA, and RM_Call. This is because, the caller, who executes the command in this context, expects a reply. Today, LUA and MULTI have a special (and different) treatment to blocking commands: LUA - Most commands are marked with no-script flag which are checked when executing and command from LUA, commands that are not marked (like XREAD) verify that their blocking mode is not used inside LUA (by checking the CLIENT_LUA client flag). MULTI - Command that is going to block, first verify that the client is not inside multi (by checking the CLIENT_MULTI client flag). If the client is inside multi, they return a result which is a match to the empty key with no timeout (for example blpop inside MULTI will act as lpop) For modules that perform RM_Call with blocking command, the returned results type is REDISMODULE_REPLY_UNKNOWN and the caller can not really know what happened....
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