After the thread in #6537 and thanks to the suggestions received, this
commit updates the original patch in order to:
1. Solve the problem of updating the time in multiple places by updating
it in call().
2. Avoid introducing a new field but use our cached time.
This required some minor refactoring to the function updating the time,
and the introduction of a new cached time in microseconds in order to
use less gettimeofday() calls.
Calling lookupKey*() many times to search a key in one command
may get different result.
That's because lookupKey*() calls expireIfNeeded(), and delete
the key when reach the expire time. So we can get an robj before
the expire time, but a NULL after the expire time.
The worst is that may lead to Redis crash, for example
`RPOPLPUSH foo foo` the first time we get a list form `foo` and
hold the pointer, but when we get `foo` again it's expired and
deleted. Now we hold a freed memory, when execute rpoplpushHandlePush()
redis crash.
To fix it, we can refactor the judgment about whether a key is expired,
using the same basetime `server.cmd_start_mstime` instead of calling
mstime() everytime.
See #6525, this likely creates a NULL deference if the client was
terminated by Redis between the creation of the blocked client and the
creation of the thread safe context.
Using the is_key_ready() callback plus the reply callback later, creates
different issues AFAIK:
1. More complex API.
2. We need to call the reply callback() ASAP if the is_key_ready()
interface returned success, however the internals do not work in that
way, so when the reply callback is called the setup could be different.
To fix that, there is to break the current design that handles the
unblocked clients asyncrhonously, and run the list ASAP.
Adding a test for coverage for RM_Call in a new "misc" unit
to be used for various short simple tests
also solves compilation warnings in redismodule.h and fork.c
As we know if a module exports module-side data types,
unload it is not allowed. This rule is the same with
blocked clients in module, because we use background
threads to implement module blocked clients, and it's
not safe to unload a module if there are background
threads running. So it's necessary to check if any
blocked clients running in this module when unload it.
Moreover, after that we can ensure that if no modules,
then no module blocked clients even module unloaded.
So, we can call moduleHandleBlockedClients only when
we have installed modules.
