Re: [RFA] choosing __platform_wait_t on targets without lock-free 64 atomics
On Thu, 12 Jan 2023 at 01:27, Thomas Rodgers wrote: > > I agree with this change. Thanks, pushed to trunk. > > On Thu, Jan 5, 2023 at 4:22 PM Jonathan Wakely wrote: >> >> How about this? >> >> I don't think we should worry about targets without atomic int, so don't >> bother using types smaller than int. >> >> >> -- >8 -- >> >> For non-futex targets the __platform_wait_t type is currently uint64_t, >> but that requires a lock in libatomic for some 32-bit targets. We don't >> really need a 64-bit type, so use unsigned long if that is lock-free, >> and int otherwise. This should mean it's lock-free on a wider set of >> targets. >> >> libstdc++-v3/ChangeLog: >> >> * include/bits/atomic_wait.h (__detail::__platform_wait_t): >> Define as unsigned long if always lock-free, and unsigned int >> otherwise. >> --- >> libstdc++-v3/include/bits/atomic_wait.h | 6 +- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/libstdc++-v3/include/bits/atomic_wait.h >> b/libstdc++-v3/include/bits/atomic_wait.h >> index bd1ed56d157..46f39f10cbc 100644 >> --- a/libstdc++-v3/include/bits/atomic_wait.h >> +++ b/libstdc++-v3/include/bits/atomic_wait.h >> @@ -64,7 +64,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION >> // and __platform_notify() if there is a more efficient primitive supported >> // by the platform (e.g. __ulock_wait()/__ulock_wake()) which is better than >> // a mutex/condvar based wait. >> -using __platform_wait_t = uint64_t; >> +# if ATOMIC_LONG_LOCK_FREE == 2 >> +using __platform_wait_t = unsigned long; >> +# else >> +using __platform_wait_t = unsigned int; >> +# endif >> inline constexpr size_t __platform_wait_alignment >>= __alignof__(__platform_wait_t); >> #endif >> -- >> 2.39.0 >>
Re: [RFA] choosing __platform_wait_t on targets without lock-free 64 atomics
I agree with this change. On Thu, Jan 5, 2023 at 4:22 PM Jonathan Wakely wrote: > How about this? > > I don't think we should worry about targets without atomic int, so don't > bother using types smaller than int. > > > -- >8 -- > > For non-futex targets the __platform_wait_t type is currently uint64_t, > but that requires a lock in libatomic for some 32-bit targets. We don't > really need a 64-bit type, so use unsigned long if that is lock-free, > and int otherwise. This should mean it's lock-free on a wider set of > targets. > > libstdc++-v3/ChangeLog: > > * include/bits/atomic_wait.h (__detail::__platform_wait_t): > Define as unsigned long if always lock-free, and unsigned int > otherwise. > --- > libstdc++-v3/include/bits/atomic_wait.h | 6 +- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/libstdc++-v3/include/bits/atomic_wait.h > b/libstdc++-v3/include/bits/atomic_wait.h > index bd1ed56d157..46f39f10cbc 100644 > --- a/libstdc++-v3/include/bits/atomic_wait.h > +++ b/libstdc++-v3/include/bits/atomic_wait.h > @@ -64,7 +64,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > // and __platform_notify() if there is a more efficient primitive > supported > // by the platform (e.g. __ulock_wait()/__ulock_wake()) which is better > than > // a mutex/condvar based wait. > -using __platform_wait_t = uint64_t; > +# if ATOMIC_LONG_LOCK_FREE == 2 > +using __platform_wait_t = unsigned long; > +# else > +using __platform_wait_t = unsigned int; > +# endif > inline constexpr size_t __platform_wait_alignment >= __alignof__(__platform_wait_t); > #endif > -- > 2.39.0 > >
Re: [RFA] choosing __platform_wait_t on targets without lock-free 64 atomics
How about this? I don't think we should worry about targets without atomic int, so don't bother using types smaller than int. -- >8 -- For non-futex targets the __platform_wait_t type is currently uint64_t, but that requires a lock in libatomic for some 32-bit targets. We don't really need a 64-bit type, so use unsigned long if that is lock-free, and int otherwise. This should mean it's lock-free on a wider set of targets. libstdc++-v3/ChangeLog: * include/bits/atomic_wait.h (__detail::__platform_wait_t): Define as unsigned long if always lock-free, and unsigned int otherwise. --- libstdc++-v3/include/bits/atomic_wait.h | 6 +- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h index bd1ed56d157..46f39f10cbc 100644 --- a/libstdc++-v3/include/bits/atomic_wait.h +++ b/libstdc++-v3/include/bits/atomic_wait.h @@ -64,7 +64,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // and __platform_notify() if there is a more efficient primitive supported // by the platform (e.g. __ulock_wait()/__ulock_wake()) which is better than // a mutex/condvar based wait. -using __platform_wait_t = uint64_t; +# if ATOMIC_LONG_LOCK_FREE == 2 +using __platform_wait_t = unsigned long; +# else +using __platform_wait_t = unsigned int; +# endif inline constexpr size_t __platform_wait_alignment = __alignof__(__platform_wait_t); #endif -- 2.39.0
