
On Sat, 15 Jun 2013 22:22:33 +1000 Nick Coghlan <ncoghlan@gmail.com> wrote:
On 15 June 2013 21:01, Antoine Pitrou <solipsis@pitrou.net> wrote:
On Sat, 15 Jun 2013 03:54:50 +0200 Victor Stinner <victor.stinner@gmail.com> wrote:
The addition of PyMem_RawMalloc() is motivated by the issue #18203 (Replace calls to malloc() with PyMem_Malloc()). The goal is to be able to setup a custom allocator for *all* allocation made by Python, so malloc() should not be called directly. PyMem_RawMalloc() is required in places where the GIL is not held (ex: in os.getcwd() on Windows).
We already had this discussion on IRC and this argument isn't very convincing to me. If os.getcwd() doesn't hold the GIL while allocating memory, then you should fix it to hold the GIL while allocating memory.
I don't like the idea of adding of third layer of allocation APIs. The dichotomy between PyObject_Malloc and PyMem_Malloc is already a bit gratuitous (i.e. not motivated by any actual real-world concern, as far as I can tell).
The only reason for the small object allocator to exist is because operating system allocators generally aren't optimised for frequent allocation and deallocation of small objects. You can gain a *lot* of speed from handling those inside the application. As the allocations grow in size, though, the application level allocator just becomes useless overhead, so it's better to delegate those operations directly to the OS.
The small object allocator *already* delegates those operations directly to the OS. You don't need a separate API to do it by hand.
For custom allocators, it's useful to be able to *ensure* you can bypass CPython's small object allocator, rather than having to rely on it being bypassed for allocations above a certain size.
Which custom allocators?
As for the debug functions you added: PyMem_GetRawAllocators(), PyMem_SetRawAllocators(), PyMem_GetAllocators(), PyMem_SetAllocators(), PyMem_SetupDebugHooks(), _PyObject_GetArenaAllocators(), _PyObject_SetArenaAllocators(). Well, do we need all *7* of them? Can't you try to make that 2 or 3?
Faux simplicity that is achieved only by failing to model a complex problem domain correctly is a bad idea (if we were satisfied with that, we could stick with the status quo).
Actually, I'm sure almost everyone *is* satisfied with the status quo here (witness the total absence of bug reports on the matter). Victor's patch addresses a rare concern compared to the common use cases of CPython. And I'm not even sure what "faux simplicity" you are talking about. What is the supposed complexity that this API is supposed to address? Why do we need two different pairs of hook-setting functions, rather than letting each function set / get all hooks at once? And why the private API functions for setting arena allocators? Memory allocation APIs are a fundamental part of the C API that many extension writers have to understand and deal with. I'm opposed to gratuitous complication when the use cases are not compelling. Regards Antoine.