sdsZmallocSize assumes a dynamically allocated SDS. When given a string
object created by createEmbeddedStringObject, it calls zmalloc_size on a
pointer that isn't the one returned by zmalloc
When HAVE_MALLOC_SIZE is false, each call to zrealloc causes used_memory
to increase by PREFIX_SIZE more than it should, due to mis-matched
accounting between the original zmalloc (which includes PREFIX size in
its increment) and zrealloc (which misses it from its decrement).
I've also supplied a command-line test to easily demonstrate the
problem. It's not wired into the test framework, because I don't know
TCL so I'm not sure how to automate it.
Storing the context is useless, because we can't really reuse that
later. For instance in the API RM_DictNext() that returns a
RedisModuleString for the next key iterated, the user should pass the
new context, because we may run the keys of the dictionary in a
different context of the one where the dictionary was created. Also the
dictionary may be created without a context, but we may still demand
automatic memory management for the returned strings while iterating.
By using the "C" suffix for functions getting pointer/len, we can do the
same in the future for other modules APIs that need a variant with
pointer/len and that are now accepting a RedisModuleString.
The burden of having to always create RedisModuleString objects within a
module context was too much, especially now that we have threaded
operations and modules are doing more interesting things. The context in
the string API is currently only used for automatic memory managemnet,
so now the API was modified so that the user can opt-out this feature by
passing a NULL context.
