This PR attempts to implement the shared memory provided by GetSharedMemoryNativeHandle. There is still more work to be done however that requires a rehaul of the current time module to handle clock contexts. This PR is mainly to get the basic functionality of the SharedMemory working and allow the use of addition to it whilst things get improved on.
Things to note:
Memory Barriers are used in the SharedMemory and a better solution would need to be done to implement this. Currently in this PR I’m faking the memory barriers as everything is sync and single threaded. They work by incrementing the counter and just populate the two data slots. On data reading, it will read the last added data.
Specific values in the shared memory would need to be updated periodically. This isn't included in this PR since we don't actively do this yet. In a later PR when time is refactored this should be done.
Finally, as we don't handle clock contexts. When time is refactored, we will need to update the shared memory for specific contexts. This PR does this already however since the contexts are all identical and not separated. We're just updating the same values for each context which in this case is empty.
Tiime:SetStandardUserSystemClockAutomaticCorrectionEnabled, Time:IsStandardUserSystemClockAutomaticCorrectionEnabled are also partially implemented in this PR. The reason the implementation is partial is because once again, a lack of clock contexts. This will be improved on in a future PR.
This PR closes issue #2556
When a destructor isn't defaulted into a cpp file, it can cause the use
of forward declarations to seemingly fail to compile for non-obvious
reasons. It also allows inlining of the construction/destruction logic
all over the place where a constructor or destructor is invoked, which
can lead to code bloat. This isn't so much a worry here, given the
services won't be created and destroyed frequently.
The cause of the above mentioned non-obvious errors can be demonstrated
as follows:
------- Demonstrative example, if you know how the described error happens, skip forwards -------
Assume we have the following in the header, which we'll call "thing.h":
\#include <memory>
// Forward declaration. For example purposes, assume the definition
// of Object is in some header named "object.h"
class Object;
class Thing {
public:
// assume no constructors or destructors are specified here,
// or the constructors/destructors are defined as:
//
// Thing() = default;
// ~Thing() = default;
//
// ... Some interface member functions would be defined here
private:
std::shared_ptr<Object> obj;
};
If this header is included in a cpp file, (which we'll call "main.cpp"),
this will result in a compilation error, because even though no
destructor is specified, the destructor will still need to be generated by
the compiler because std::shared_ptr's destructor is *not* trivial (in
other words, it does something other than nothing), as std::shared_ptr's
destructor needs to do two things:
1. Decrement the shared reference count of the object being pointed to,
and if the reference count decrements to zero,
2. Free the Object instance's memory (aka deallocate the memory it's
pointing to).
And so the compiler generates the code for the destructor doing this inside main.cpp.
Now, keep in mind, the Object forward declaration is not a complete type. All it
does is tell the compiler "a type named Object exists" and allows us to
use the name in certain situations to avoid a header dependency. So the
compiler needs to generate destruction code for Object, but the compiler
doesn't know *how* to destruct it. A forward declaration doesn't tell
the compiler anything about Object's constructor or destructor. So, the
compiler will issue an error in this case because it's undefined
behavior to try and deallocate (or construct) an incomplete type and
std::shared_ptr and std::unique_ptr make sure this isn't the case
internally.
Now, if we had defaulted the destructor in "thing.cpp", where we also
include "object.h", this would never be an issue, as the destructor
would only have its code generated in one place, and it would be in a
place where the full class definition of Object would be visible to the
compiler.
---------------------- End example ----------------------------
Given these service classes are more than certainly going to change in
the future, this defaults the constructors and destructors into the
relevant cpp files to make the construction and destruction of all of
the services consistent and unlikely to run into cases where forward
declarations are indirectly causing compilation errors. It also has the
plus of avoiding the need to rebuild several services if destruction
logic changes, since it would only be necessary to recompile the single
cpp file.
