Re: [dpdk-dev] [PATCH v6 01/10] eal: add thread id and simple thread functions

[Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>]

2021-04-29 13:05 (UTC+0100), Kinsella, Ray:
> On 29/04/2021 08:44, Thomas Monjalon wrote:
> > 29/04/2021 02:50, Dmitry Kozlyuk:  
> >> 2021-04-02 18:38 (UTC-0700), Narcisa Ana Maria Vasile:  
> >>> --- /dev/null
> >>> +++ b/lib/librte_eal/windows/include/rte_windows_thread_types.h
> >>> @@ -0,0 +1,12 @@
> >>> +/* SPDX-License-Identifier: BSD-3-Clause
> >>> + * Copyright(c) 2021 Microsoft Corporation
> >>> + */
> >>> +
> >>> +#ifndef _RTE_THREAD_TYPES_H_
> >>> +#define _RTE_THREAD_TYPES_H_
> >>> +
> >>> +#include <rte_windows.h>
> >>> +
> >>> +typedef DWORD                       rte_thread_t;
> >>> +
> >>> +#endif /* _RTE_THREAD_TYPES_H_ */  
> >>
> >> pthread_t type in pthreads-win32 and winpthread is not 32 bit.
> >> DPDK will have different ABI depending on a threading backend used.
> >> Apps must know it at build time then. How do they discover it?
> >> This is worth a warning in commit log and docs.  
> > 
> > Not sure this is an acceptable behaviour.
> > In my opinion, ABI should not vary.
> > +Cc Ray
> >   
> 
> So pthread_t on Win32 should just map to the HANDLE datatype.
> Which if memory serves is in fact a DWORD on Win32.

DWORD = uint32_t, HANDLE = void*, which are of different size on x64.
I suggest an opaque 64-bit value to fit pthread_t from MinGW's winpthread.
Only pthreads-win32 has a bigger pthread_t, but we don't have to support it.

> So I suspect that pthreads indirection is probably be just providing a circuitous route to end up in the same place, a HANDLE
> 
> IMHO
> To absolutely guarantee no ABI change, we ought to be passing back void * not rte_thread_t. 

Yes. Only I'd use a type-safe version:

	typedef struct rte_thread_tag {
		void *opaque; /* or uintptr_t per Tyler's suggestion */
	} rte_thread_t;