[libcamera-devel] [RFC PATCH 1/6] libcamera: base: Add thread safety annotation macros

[Umang Jain]

Hi Hiro,

Thank you for the patch.

On 10/29/21 9:44 AM, Hirokazu Honda wrote:
> Clang complier is able to do a thread safety analysis with
> annotations [1]. This introduces the thread safety annotation
> macros and also enable the analysis by adding -Wthread-safety
> if a clang compiler is used.
>
> [1] https://clang.llvm.org/docs/ThreadSafetyAnalysis.html.


Ok so this boilerplate for annotation is taken from the above link 
itself. I realized it later (since it's at the end of the link)

>
> Signed-off-by: Hirokazu Honda <hiroh at chromium.org>
> ---
>   include/libcamera/base/meson.build          |   1 +
>   include/libcamera/base/thread_annotations.h | 151 ++++++++++++++++++++
>   meson.build                                 |   1 +
>   3 files changed, 153 insertions(+)
>   create mode 100644 include/libcamera/base/thread_annotations.h
>
> diff --git a/include/libcamera/base/meson.build b/include/libcamera/base/meson.build
> index 525aba9d..1a71ce5a 100644
> --- a/include/libcamera/base/meson.build
> +++ b/include/libcamera/base/meson.build
> @@ -19,6 +19,7 @@ libcamera_base_headers = files([
>       'signal.h',
>       'span.h',
>       'thread.h',
> +    'thread_annotations.h',
>       'timer.h',
>       'utils.h',
>   ])
> diff --git a/include/libcamera/base/thread_annotations.h b/include/libcamera/base/thread_annotations.h


I am contemplating a bit about putting this inside -base. I see you have 
also introduced

          include/libcamera/base/mutex.h

in subsequent patches. IMO, this intends to be a internal class to 
libcamera so, I believe include/libcamera/internal would be a better 
location? What do you think?

I would like to have other's opinion as well, but do not consider a 
major blocker for the series. We can figure this out as we go along.

> new file mode 100644
> index 00000000..935d8799
> --- /dev/null
> +++ b/include/libcamera/base/thread_annotations.h
> @@ -0,0 +1,151 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2021, Google Inc.
> + *
> + * thread_annotation.h - Macro of Clang thread safety analysis
> + */
> +#ifndef __LIBCAMERA_BASE_THREAD_ANNOTATIONS_H__
> +#define __LIBCAMERA_BASE_THREAD_ANNOTATIONS_H__
> +
> +/*
> + * Enable thread safety attributes only with clang.
> + * The attributes can be safely erased when compiling with other compilers.
> + */
> +#if defined(__clang__) && (!defined(SWIG))
> +#define THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))
> +#else
> +#define THREAD_ANNOTATION_ATTRIBUTE__(x) /* no-op */
> +#endif
> +
> +/* See https://clang.llvm.org/docs/ThreadSafetyAnalysis.html for these usages. */
> +
> +#define CAPABILITY(x)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(capability(x))
> +
> +#define SCOPED_CAPABILITY				\
> +	THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
> +
> +#define GUARDED_BY(x)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
> +
> +#define PT_GUARDED_BY(x)				\
> +	THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))
> +
> +#define ACQUIRED_BEFORE(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(__VA_ARGS__))
> +
> +#define ACQUIRED_AFTER(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(__VA_ARGS__))
> +
> +#define REQUIRES(...)							\
> +	THREAD_ANNOTATION_ATTRIBUTE__(requires_capability(__VA_ARGS__))
> +
> +#define REQUIRES_SHARED(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(requires_shared_capability(__VA_ARGS__))
> +
> +#define ACQUIRE(...)							\
> +	THREAD_ANNOTATION_ATTRIBUTE__(acquire_capability(__VA_ARGS__))
> +
> +#define ACQUIRE_SHARED(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(acquire_shared_capability(__VA_ARGS__))
> +
> +#define RELEASE(...)							\
> +	THREAD_ANNOTATION_ATTRIBUTE__(release_capability(__VA_ARGS__))
> +
> +#define RELEASE_SHARED(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(release_shared_capability(__VA_ARGS__))
> +
> +#define RELEASE_GENERIC(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(release_generic_capability(__VA_ARGS__))
> +
> +#define TRY_ACQUIRE(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_capability(__VA_ARGS__))
> +
> +#define TRY_ACQUIRE_SHARED(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_shared_capability(__VA_ARGS__))
> +
> +#define EXCLUDES(...)							\
> +	THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(__VA_ARGS__))
> +
> +#define ASSERT_CAPABILITY(x)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(assert_capability(x))
> +
> +#define ASSERT_SHARED_CAPABILITY(x)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_capability(x))
> +
> +#define RETURN_CAPABILITY(x)				\
> +	THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))
> +
> +#define NO_THREAD_SAFETY_ANALYSIS					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
> +
> +#ifdef USE_LOCK_STYLE_THREAD_SAFETY_ATTRIBUTES
> +/*
> + * The original version of thread safety analysis the following attribute
> + * definitions.  These use a lock-based terminology.  They are still in use
> + * by existing thread safety code, and will continue to be supported.
> + */
> +
> +/* Deprecated. */
> +#define PT_GUARDED_VAR					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_var)
> +
> +/* Deprecated. */
> +#define GUARDED_VAR					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(guarded_var)
> +
> +/* Replaced by REQUIRES */
> +#define EXCLUSIVE_LOCKS_REQUIRED(...)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(exclusive_locks_required(__VA_ARGS__))
> +
> +/* Replaced by REQUIRES_SHARED */
> +#define SHARED_LOCKS_REQUIRED(...)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(shared_locks_required(__VA_ARGS__))
> +
> +/* Replaced by CAPABILITY */
> +#define LOCKABLE				\
> +	THREAD_ANNOTATION_ATTRIBUTE__(lockable)
> +
> +/* Replaced by SCOPED_CAPABILITY */
> +#define SCOPED_LOCKABLE					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
> +
> +/* Replaced by ACQUIRE */
> +#define EXCLUSIVE_LOCK_FUNCTION(...)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(exclusive_lock_function(__VA_ARGS__))
> +
> +/* Replaced by ACQUIRE_SHARED */
> +#define SHARED_LOCK_FUNCTION(...)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(shared_lock_function(__VA_ARGS__))
> +
> +/* Replaced by RELEASE and RELEASE_SHARED */
> +#define UNLOCK_FUNCTION(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(unlock_function(__VA_ARGS__))
> +
> +/* Replaced by TRY_ACQUIRE */
> +#define EXCLUSIVE_TRYLOCK_FUNCTION(...)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(exclusive_trylock_function(__VA_ARGS__))
> +
> +/* Replaced by TRY_ACQUIRE_SHARED */
> +#define SHARED_TRYLOCK_FUNCTION(...)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(shared_trylock_function(__VA_ARGS__))
> +
> +/* Replaced by ASSERT_CAPABILITY */
> +#define ASSERT_EXCLUSIVE_LOCK(...)					\
> +	THREAD_ANNOTATION_ATTRIBUTE__(assert_exclusive_lock(__VA_ARGS__))
> +
> +/* Replaced by ASSERT_SHARED_CAPABILITY */
> +#define ASSERT_SHARED_LOCK(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_lock(__VA_ARGS__))
> +
> +/* Replaced by EXCLUDE_CAPABILITY */
> +#define LOCKS_EXCLUDED(...)						\
> +	THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(__VA_ARGS__))
> +
> +/* Replaced by RETURN_CAPABILITY */
> +#define LOCK_RETURNED(x)				\
> +	THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))
> +
> +#endif /* USE_LOCK_STYLE_THREAD_SAFETY_ATTRIBUTES */
> +
> +#endif /* __LIBCAMERA_BASE_THREAD_ANNOTATIONS_H__ */
> diff --git a/meson.build b/meson.build
> index 7892a9e3..7147a108 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -72,6 +72,7 @@ if cc.get_id() == 'clang'
>   
>       cpp_arguments += [
>           '-Wextra-semi',
> +        '-Wthread-safety',
>       ]
>   endif
>