This is not perfect, and we need to more thoroughly address thread safety in the PRC system, but it will nonetheless address a lot of the race condition issues when querying these variables from two threads at the same time.
This reimplements the spinlock on top of std::atomic_flag, which is guaranteed to be lockless. It also inserts the PAUSE (REP NOP) instruction which is strongly recommended to be placed in busy-wait loops by Intel.
This also includes a recursive spinlock implementation.
The spinlock implementation is disabled by default, but can be enabled by adding the --override MUTEX_SPINLOCK=1 flag to makepanda.
For example, this will let us pass a ConfigVariableFilename to anything that accepts a Filename, just like in C++.
Does not work if the return value if the typecast operator requires management.
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.
Only the basics are supported; the __members__ or iter interface is not supported at this time.
See also #351 for discussion on pulling in enum34 module.
If a class inherits from ReferenceCount, it can be destructed by downcasting to ReferenceCount, so it should not be an obstacle to properly clean it up when such a class is returned from C++.
This issue comes up when a CycleData is returned via MemoryUsagePointers, which is not exposed so is wrapped as NodeReferenceCount instead, which has a protected destructor.
If any code is relying on this, please let me know and I will add it back. It appears to be redundant, though, since one can access DtoolClassDict directly.
Symbol kept around temporarily in order to keep ABI compatibility for a short while as people may not update their interrogate and Panda in sync, but it can soon be removed.
rdb
Sam Edwards
Mitchell Stokes