[PATCH] libstdc++: Add support for C++20 barriers

Jonathan Wakely jwakely@redhat.com
Wed Nov 4 18:52:59 GMT 2020


On 04/11/20 10:41 -0800, Thomas Rodgers wrote:
>From: Thomas Rodgers <trodgers@redhat.com>
>
>IGNORE the previous version of this patch please.

OK, but all my comments seem to apply to this one too.

>Adds <barrier>
>
>libstdc++/ChangeLog:
>
>	* include/Makefile.am (std_headers): Add new header.
>	* include/Makefile.in: Regenerate.
>	* include/std/barrier: New file.
>	* testsuite/30_thread/barrier/1.cc: New test.
>	* testsuite/30_thread/barrier/2.cc: Likewise.
>	* testsuite/30_thread/barrier/arrive_and_drop.cc: Likewise.
>	* testsuite/30_thread/barrier/arrive_and_wait.cc: Likewise.
>	* testsuite/30_thread/barrier/arrive.cc: Likewise.
>	* testsuite/30_thread/barrier/completion.cc: Likewise.
>	* testsuite/30_thread/barrier/max.cc: Likewise.
>---
> libstdc++-v3/include/Makefile.am              |   1 +
> libstdc++-v3/include/Makefile.in              |   1 +
> libstdc++-v3/include/bits/atomic_base.h       |  11 +-
> libstdc++-v3/include/std/barrier              | 248 ++++++++++++++++++
> libstdc++-v3/include/std/version              |   1 +
> .../testsuite/30_threads/barrier/1.cc         |  27 ++
> .../testsuite/30_threads/barrier/2.cc         |  27 ++
> .../testsuite/30_threads/barrier/arrive.cc    |  51 ++++
> .../30_threads/barrier/arrive_and_drop.cc     |  49 ++++
> .../30_threads/barrier/arrive_and_wait.cc     |  51 ++++
> .../30_threads/barrier/completion.cc          |  54 ++++
> .../testsuite/30_threads/barrier/max.cc       |  44 ++++
> 12 files changed, 562 insertions(+), 3 deletions(-)
> create mode 100644 libstdc++-v3/include/std/barrier
> create mode 100644 libstdc++-v3/testsuite/30_threads/barrier/1.cc
> create mode 100644 libstdc++-v3/testsuite/30_threads/barrier/2.cc
> create mode 100644 libstdc++-v3/testsuite/30_threads/barrier/arrive.cc
> create mode 100644 libstdc++-v3/testsuite/30_threads/barrier/arrive_and_drop.cc
> create mode 100644 libstdc++-v3/testsuite/30_threads/barrier/arrive_and_wait.cc
> create mode 100644 libstdc++-v3/testsuite/30_threads/barrier/completion.cc
> create mode 100644 libstdc++-v3/testsuite/30_threads/barrier/max.cc
>
>diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
>index 382e94322c1..9e497835ee0 100644
>--- a/libstdc++-v3/include/Makefile.am
>+++ b/libstdc++-v3/include/Makefile.am
>@@ -30,6 +30,7 @@ std_headers = \
> 	${std_srcdir}/any \
> 	${std_srcdir}/array \
> 	${std_srcdir}/atomic \
>+	${std_srcdir}/barrier \
> 	${std_srcdir}/bit \
> 	${std_srcdir}/bitset \
> 	${std_srcdir}/charconv \
>diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
>index dd4db926592..1ad34719d3e 100644
>--- a/libstdc++-v3/include/bits/atomic_base.h
>+++ b/libstdc++-v3/include/bits/atomic_base.h
>@@ -603,13 +603,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>       }
>
> #if __cplusplus > 201703L
>+      template<typename _Func>
>+	_GLIBCXX_ALWAYS_INLINE void
>+	_M_wait(__int_type __old, const _Func& __fn) const noexcept
>+	{ std::__atomic_wait(&_M_i, __old, __fn); }
>+
>       _GLIBCXX_ALWAYS_INLINE void
>       wait(__int_type __old,
> 	  memory_order __m = memory_order_seq_cst) const noexcept
>       {
>-	std::__atomic_wait(&_M_i, __old,
>-			   [__m, this, __old]
>-			   { return this->load(__m) != __old; });
>+	_M_wait(__old,
>+		[__m, this, __old]
>+		{ return this->load(__m) != __old; });
>       }

This looks like it's not meant to be part of this patch.

It also looks wrong for any patch, because it adds _M_wait as a public
member.

Not sure what this piece is for :-)




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