RE: [PATCH v5 1/3] eal: add basic thread ID and current thread identifier API

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Konstantin Ananyev [mailto:konstantin.v.ananyev@yandex.ru]
> Sent: Friday, 6 May 2022 21.38
> 
> 05/05/2022 08:11, Tyler Retzlaff пишет:
> > On Wed, May 04, 2022 at 11:55:57PM +0100, Konstantin Ananyev wrote:
> >> 04/05/2022 16:46, Tyler Retzlaff пишет:
> >>> Provide a portable type-safe thread identifier.
> >>> Provide rte_thread_self for obtaining current thread identifier.
> >>>
> >>> Signed-off-by: Narcisa Vasile <navasile@microsoft.com>
> >>> Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> >>> Acked-by: Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>
> >>> ---
> >>>   lib/eal/include/rte_thread.h | 22 ++++++++++++++++++++++
> >>>   lib/eal/unix/rte_thread.c    | 11 +++++++++++
> >>>   lib/eal/version.map          |  3 +++
> >>>   lib/eal/windows/rte_thread.c | 10 ++++++++++
> >>>   4 files changed, 46 insertions(+)
> >>>
> >>> diff --git a/lib/eal/include/rte_thread.h
> b/lib/eal/include/rte_thread.h
> >>> index 8be8ed8..14478ba 100644
> >>> --- a/lib/eal/include/rte_thread.h
> >>> +++ b/lib/eal/include/rte_thread.h
> >>> @@ -1,7 +1,10 @@
> >>>   /* SPDX-License-Identifier: BSD-3-Clause
> >>>    * Copyright(c) 2021 Mellanox Technologies, Ltd
> >>> + * Copyright (C) 2022 Microsoft Corporation
> >>>    */
> >>> +#include <stdint.h>
> >>> +
> >>>   #include <rte_os.h>
> >>>   #include <rte_compat.h>
> >>> @@ -21,10 +24,29 @@
> >>>   #endif
> >>>   /**
> >>> + * Thread id descriptor.
> >>> + */
> >>> +typedef struct {
> >>> +	uintptr_t opaque_id; /**< thread identifier */
> >>
> >>
> >> I know that currently on linux typeof(pthread_id) == unsigned long
> int.
> >> Though wouldn't it be safer and cleaner to use pthread_t explicitly
> >> on posix-like systems?
> >
> > i believe the previous discussions are.
> >
> > * preference for reduced or no conditional compilation.
> > * preference for sizeof(type) to be `the same' on all platforms.
> 
> 
> It would be the same as long as sizes of pthread_t uintptr_t are equal.

They are not. pthread_t (Linux thread ID) and DWORD (Windows thread ID) are both 32 bit, uintptr_t is 64 or 32 bit depending on pointer size (32 or 64 bit CPU).

> 
> > * preference for platform agnostic headers. i.e. don't drag
> >    platform specific headers into the application namespace when
> >    including rte_xxx.h headers.
> >> Something like:
> >> typedef struct {
> >> #ifdef WINDOWS
> >> 	uintptr_t opaque_id;
> >> #else
> >> 	pthread_t opaque_id;
> >> #endif
> >> };
> >> AFAIK POSIX itself doesn't require pthread_t to be an 'arithmetic
> type'.
> >
> > yes, this is correct. newer posix introduced this to allow the use of
> > structs. i assume prior reviewers are aware of the recent posix
> > standard (or should be).
> >
> > this type makes no attempt to be usable on platforms that use
> > a handle > sizeof(uintptr_t). though any platform that does is free
> > to shove a pointer to struct into the handle at the cost of a
> > dereference if that is their implementation.
> 
> Using pthread_t directly still seems like a safest bet to me.
> Then we can avoid doing these explicit type conversions before/after
> each pthread_xxx() call and wouldn't need to worry if we'll ever have
> platform with bigger pthread_t (though yes, I admit it is very
> unlikely).
> But, if we still prefer to go ahead with 'arch-neutral' approach,
> then I think we need to have compilation time check that opaque_id
> is big enough to hold pthread_t value:
> RTE_BUILD_BUG_ON(sizeof(pthread_t) != sizeof(opaque_id)) or so.
> 

I agree with Konstantin's concerns. All this type casting increases the risk for bugs. Also, I don't understand the need to use a 64 bit value when thread IDs are 32 bit in both Linux and Windows.

The thread handling is O/S specific code, so #ifdef is unavoidable.

Furthermore, I don't think we should wrap O/S specific integer types into structs - it adds unnecessary complexity.

I would prefer:

#ifdef WINDOWS
typedef DWORD rte_thread_t;
#else
typedef pthread_t rte_thread_t;
#endif

> 
> >
> >>
> >>
> >>> +} rte_thread_t;
> >>> +
> >>> +/**
> >>>    * TLS key type, an opaque pointer.
> >>>    */
> >>>   typedef struct eal_tls_key *rte_thread_key;
> >>> +/**
> >>> + * @warning
> >>> + * @b EXPERIMENTAL: this API may change without prior notice.
> >>> + *
> >>> + * Get the id of the calling thread.
> >>> + *
> >>> + * @return
> >>> + *   Return the thread id of the calling thread.
> >>> + */
> >>> +__rte_experimental
> >>> +rte_thread_t rte_thread_self(void);
> >>> +
> >>>   #ifdef RTE_HAS_CPUSET
> >>>   /**
> >>> diff --git a/lib/eal/unix/rte_thread.c b/lib/eal/unix/rte_thread.c
> >>> index c34ede9..82e008f 100644
> >>> --- a/lib/eal/unix/rte_thread.c
> >>> +++ b/lib/eal/unix/rte_thread.c
> >>> @@ -1,5 +1,6 @@
> >>>   /* SPDX-License-Identifier: BSD-3-Clause
> >>>    * Copyright 2021 Mellanox Technologies, Ltd
> >>> + * Copyright (C) 2022 Microsoft Corporation
> >>>    */
> >>>   #include <errno.h>
> >>> @@ -15,6 +16,16 @@ struct eal_tls_key {
> >>>   	pthread_key_t thread_index;
> >>>   };
> >>> +rte_thread_t
> >>> +rte_thread_self(void)
> >>> +{
> >>> +	rte_thread_t thread_id;
> >>> +
> >>> +	thread_id.opaque_id = (uintptr_t)pthread_self();
> >>> +
> >>> +	return thread_id;
> >>> +}
> >>> +
> >>>   int
> >>>   rte_thread_key_create(rte_thread_key *key, void
> (*destructor)(void *))
> >>>   {
> >>> diff --git a/lib/eal/version.map b/lib/eal/version.map
> >>> index b53eeb3..05ce8f9 100644
> >>> --- a/lib/eal/version.map
> >>> +++ b/lib/eal/version.map
> >>> @@ -420,6 +420,9 @@ EXPERIMENTAL {
> >>>   	rte_intr_instance_free;
> >>>   	rte_intr_type_get;
> >>>   	rte_intr_type_set;
> >>> +
> >>> +	# added in 22.07
> >>> +	rte_thread_self;
> >>>   };
> >>>   INTERNAL {
> >>> diff --git a/lib/eal/windows/rte_thread.c
> b/lib/eal/windows/rte_thread.c
> >>> index 667287c..59fed3c 100644
> >>> --- a/lib/eal/windows/rte_thread.c
> >>> +++ b/lib/eal/windows/rte_thread.c
> >>> @@ -11,6 +11,16 @@ struct eal_tls_key {
> >>>   	DWORD thread_index;
> >>>   };
> >>> +rte_thread_t
> >>> +rte_thread_self(void)
> >>> +{
> >>> +	rte_thread_t thread_id;
> >>> +
> >>> +	thread_id.opaque_id = GetCurrentThreadId();
> >>> +
> >>> +	return thread_id;
> >>> +}
> >>> +
> >>>   int
> >>>   rte_thread_key_create(rte_thread_key *key,
> >>>   		__rte_unused void (*destructor)(void *))
>