This is done using a Python extension function, which also happens to make the call more efficient as this avoids an extra copy. The C++ version still returns std::string as there is still a lot of C++ code that relies on that.
Fixes#297
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.
This is inefficient because it induces an unnecessary ref()/unref() pair when we just need to move the pointer out of the function. Thanks to 23128e4695, we can now move between related pointer types, making the .p() hack unnecessary.
This makes it possible to implicitly convert a PT of a derived type to a (C)PT of a base type, without needing to first convert it to a regular pointer. This also applies to moves, which are now more efficient due to the lack of need for ref/unref pair even if the pointer type is not exactly the same.
I'm not sure why they were ifdeffed out, but they should certainly be available so that it is possible to compare WeakPointerTo in a thread-safe manner.
This came up in #330; the Character destructor caused something to call lock() on a weak pointer to that character, which would induce a ref() and unref() pair, but since the refcount was 0, this would call the destructor and thereby create infinite recursion.
I considered instead calling mark_deleted() inside unref() so that the callbacks get to run before the object is actually deleted, and was_deleted() will become true as soon as unref() reaches 0. However, this would require grabbing the lock in unref() to be fully thread-safe, since we would need to bring the refcount to 0 and mark the object as deleted in one atomic operation, so this would be an unacceptable general performance penalty.
Instead, WeakPointerTo::lock() now atomically increments the reference count if it is not already zero, and returns null otherwise. This should be safe because the object cannot be deleted while the WeakReferenceList lock is held.
This renames acquire/release to lock/unlock in order to be compatible with std::lock_guard and std::unique_lock (which will eventually replace the *MutexHolder classes). It will also allow us to typedef MutexImpl to std::mutex later on.
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 distinction allows us to better support Python 3, since it will raise exceptions when trying to put arbitrary binary data in a str object.
This also adds some convenience functions for efficiently initializing a Datagram or PTA_uchar from a vector_uchar.
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.
- Return vector_uchar from readSubfile instead of
string. This will correct problems with Python 3 unicode
strings and will return bytes instead.
Signed-off-by: deflected <deflected@users.noreply.github.com>
Closes#290
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.
Sam Edwards
rdb
Younguk Kim
deflected