Fix double initialization of Database class

[ArturKnopik]

Fix double initialization of Database class, Database now become true singleton

Pull Request Prelude

• I have followed [proper The Forgotten Server code styling][code].
• I have read and understood the [contribution guidelines][cont] before making this PR.
• I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

Issues addressed:

[nekiro]

DatabaseTasks operates in its own thread, currently with this change you access the singleton from two different threads simultaneously. This code now is probably not thread safe, thus broken unless I'm missing something here
database has mutex inside :)

[ArturKnopik]

Good point, need to be checked
Will be nice to add some job that will check memory leaks and synchronization
@edit
mutex confirmed

[kygov]

So database tasks are no longer asynchronously?

https://github.com/otland/forgottenserver/blob/master/src/luascript.cpp#L4184
https://github.com/otland/forgottenserver/blob/master/src/luascript.cpp#L4224

[nekiro]

So database tasks are no longer asynchronously?

https://github.com/otland/forgottenserver/blob/master/src/luascript.cpp#L4184 https://github.com/otland/forgottenserver/blob/master/src/luascript.cpp#L4224

They are, using the same instance doesn't make it synchronous, but in special cases where simultaneous access could occur it will not cause undefined behaviour. If you mean it will not execute at the same time, it never did, mysql has to queue these actions anyway for obvious reasons. Asynchronous in this case means don't block main thread. I'm not exactly sure how does it behave with long queries for example in DatabaseTasks, cause this would block the thread (due to mutex locking) and then hang the main thread, which is something we don't want, so you might be onto something here

[kygov]

AFAIK previous it had its own connection to mysql and you could execute two queries in same time if they were not to same table (then mysql would queue it).
I will check it later.

[nekiro]

AFAIK previous it had its own connection to mysql and you could execute two queries in same time if they were not to same table (then mysql would queue it). I will check it later.

Yup, this PR is most likely a revert xD