For this reason, the function above contains two implementations, depending on whether __cpp_lib_atomic_shared_ptr is supported.
Both implementations are problematic:
The implementation is not thread-safe when __cpp_lib_atomic_shared_ptr is unsupported. The object would need to carry a pointer to mutex for that.
The implementation when __cpp_lib_atomic_shared_ptr is supported is also unsafe because the load and exchange operations are independent. This means two concurrent threads will attempt to construct the object twice if they call the function before the object is constructed.
vinniefalco
commented
1 week ago
Most compilers don't implement
__cpp_lib_atomic_shared_ptr, on whichLazyObjectImpldepends:https://github.com/cppalliance/mrdocs/blob/a962db0fc4a309afa11e956fbe9b9880e39c92f0/src/lib/Dom/Object.cpp#L216-L232
For this reason, the function above contains two implementations, depending on whether
__cpp_lib_atomic_shared_ptris supported.Both implementations are problematic:
__cpp_lib_atomic_shared_ptris unsupported. The object would need to carry a pointer to mutex for that.__cpp_lib_atomic_shared_ptris supported is also unsafe because the load and exchange operations are independent. This means two concurrent threads will attempt to construct the object twice if they call the function before the object is constructed.