[Feature Request] C++: Create arena based allocator and have access to it

[AndreyOrb]

Describe the feature request

I would like to reuse a global allocator.

With api.CreateAndRegisterAllocatorV2 I can create global allocator, but I still have no access to it.

With api.CreateAllocator I can create one and have access to it, but it requires a session as a parameter.
So, I need to create a session with some dummy graph first.

Describe scenario use case

With an access to allocator, I can reuse it to pre-allocate tensors (not with bindings), to know current utilization of a memory, etc.

It can be a new api.GetAllocator method or api.CreateAllocator without session

[pranavsharma]

Does this work for you?

onnxruntime/include/onnxruntime/core/session/onnxruntime_c_api.h

Lines 1624 to 1632 in b2aec41

	/** \brief Get the default allocator
	*
	* The default allocator is a CPU based, non-arena. Always returns the same pointer to the same default allocator.
	*
	* \param[out] out Returned value should NOT be freed
	*
	* \snippet{doc} snippets.dox OrtStatus Return Value
	*/
	ORT_API2_STATUS(GetAllocatorWithDefaultOptions, _Outptr_ OrtAllocator** out);

. I assume you're looking for a CPU allocator only.

[AndreyOrb]

I'm actually looking for both CPU and GPU allocators.