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.
This remove support for coercing non-ReferenceCounted types that are neither default-constructible nor move-assignable, but it turns out none of the classes we really need it for matches that.
It further cuts down on the amount of code that is being generated to support coercion in cases where it makes absolutely no sense.
rdb
Sam Edwards
deflected
wolfgangp