eden-emu/eden - eden - InfoTonic

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Tree: 0030e8072a

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Author	SHA1	Message	Date
Zach Hilman	0030e8072a	bcat: Add commands to create IDeliveryCacheStorageService Used to access contents of download.	7 years ago
Lioncash	8a9b062587	hle/service: Default constructors and destructors in the cpp file where applicable 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.	7 years ago
mailwl	3c612dea08	Service/BCAT: add module and services	8 years ago

Author

SHA1

Message

Date

Zach Hilman

0030e8072a

bcat: Add commands to create IDeliveryCacheStorageService

Used to access contents of download.

7 years ago

Lioncash

8a9b062587

hle/service: Default constructors and destructors in the cpp file where applicable

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.

7 years ago

mailwl

3c612dea08

Service/BCAT: add module and services

8 years ago

3 Commits (0030e8072a7f7bfb6948b90414d54b11c670907b)