Even a brief error message in the assertion is infinitely more useful to a user who is not at home in the source code, especially for assertions that may reasonably be triggered by honest user mistakes.
Currently, the WeakPointerTo comparison operators compare the raw pointers, but this is not useful as it may cause a false equality if one weak pointer in the comparison is expired and points to memory that has since been reused.
Instead, we can define a comparison based on the control block pointer, which exists since the new weak pointer implementation in 0bb81a43c9. This is implemented in the owner_before method, matching C++11 std::weak_ptr semantics.
I would now recommend deprecating most comparison operators of WeakPointerTo or redefining them to make more sense, ie. comparing equal if they (once) referred to the same object and not if they simply point to the same memory address. This has not yet been done, though code that uses the comparison operators has been fixed in this commit.
Overloads of std::owner_less have been provided for creating a map or set with Weak(Const)PointerTo keys.
To access a WeakPointerTo in a thread-safe way, use something like this:
if (auto ptr = weak_ptr.lock()) {
..use ptr as regular PointerTo
}
The new implementation no longer needs a reference to be stored to all weak pointers on the WeakReferenceList; a mere count of weak pointers is sufficient. Therefore, callbacks theoretically no longer require a WeakPointerTo to be constructed.
The WeakPointerTo class is not actually atomic; it could be made so, but I don't believe it's worth it at this time.
This is designed to sanity-check the buildsystem, ensuring that the
expected BUILDING_ macros are defined at the expected time. It
also helps catch cases where the wrong BUILDING_/EXPCL_ macros
are used.
The GCC documentation states that, as of GCC 2.7.2, these aren't
necessary for proper program behavior. The documentation further
discourages their use because they don't suppress unnecessary code
duplication.
The Panda codebase these days uses "extern template class" instead,
which tells the compiler not to perform implicit template expansion
because an explicit template expansion is available for linking
elsewhere in the program. This is a more compiler-neutral way of
achieving the same thing as '#pragma interface', making
'#pragma interface' not only redundant, it could also mask problems
in the "extern template class" machinery.
rdb
Sam Edwards
Younguk Kim