From 7c21556daf385fe9ece37319f574776dd7d8ab1c Mon Sep 17 00:00:00 2001 From: Thomas W Rodgers Date: Fri, 22 Apr 2022 15:46:19 -0700 Subject: [PATCH] libstdc++: Make atomic notify_one and notify_all non-const PR102994 "atomics: std::atomic::wait is not marked const" raises the issue that the current libstdc++ implementation marks the notify members const, the implementation strategy used by libstdc++, as well as libc++ and the Microsoft STL, do not require the atomic to be mutable (it is hard to conceive of a desirable implementation approach that would require it). The original paper proposing the wait/notify functionality for atomics (p1185) also had these members marked const for the first three revisions, but that was changed without explanation in r3 and subsequent revisions of the paper. After raising the issue to the authors of p1185 and the author of the libc++ implementation, the consensus seems to be "meh, it's harmless" so there seems little appetite for an LWG issue to revisit the subject. This patch changes the libstdc++ implementation to be in agreement with the standard by removing const from those notify_one/notify_all members. libstdc++-v3/ChangeLog: PR libstdc++/102994 * include/bits/atomic_base.h (atomic_flag::notify_one, notify_all): Remove const qualification. (__atomic_base::notify_one, notify_all): Likewise. * include/std/atomic (atomic::notify_one, notify_all): Likewise. (atomic::notify_one, notify_all): Likewise. (atomic::notify_one, notify_all): Likewise. (atomic_notify_one, atomic_notify_all): Likewise. * testsuite/29_atomics/atomic/wait_notify/102994.cc: Adjust test to account for change in notify_one/notify_all signature. --- libstdc++-v3/include/bits/atomic_base.h | 8 ++++---- libstdc++-v3/include/std/atomic | 16 ++++++++-------- .../testsuite/29_atomics/atomic/wait_notify/102994.cc | 4 ++-- 3 files changed, 14 insertions(+), 14 deletions(-) diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h index 2cad848..5cf217d 100644 --- a/libstdc++-v3/include/bits/atomic_base.h +++ b/libstdc++-v3/include/bits/atomic_base.h @@ -252,13 +252,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // TODO add const volatile overload _GLIBCXX_ALWAYS_INLINE void - notify_one() const noexcept + notify_one() noexcept { std::__atomic_notify_address(&_M_i, false); } // TODO add const volatile overload _GLIBCXX_ALWAYS_INLINE void - notify_all() const noexcept + notify_all() noexcept { std::__atomic_notify_address(&_M_i, true); } // TODO add const volatile overload @@ -600,13 +600,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // TODO add const volatile overload _GLIBCXX_ALWAYS_INLINE void - notify_one() const noexcept + notify_one() noexcept { std::__atomic_notify_address(&_M_i, false); } // TODO add const volatile overload _GLIBCXX_ALWAYS_INLINE void - notify_all() const noexcept + notify_all() noexcept { std::__atomic_notify_address(&_M_i, true); } // TODO add const volatile overload diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic index bc57659..d819b6b 100644 --- a/libstdc++-v3/include/std/atomic +++ b/libstdc++-v3/include/std/atomic @@ -172,11 +172,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // TODO add const volatile overload void - notify_one() const noexcept + notify_one() noexcept { _M_base.notify_one(); } void - notify_all() const noexcept + notify_all() noexcept { _M_base.notify_all(); } #endif // __cpp_lib_atomic_wait }; @@ -399,11 +399,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // TODO add const volatile overload void - notify_one() const noexcept + notify_one() noexcept { std::__atomic_notify_address(&_M_i, false); } void - notify_all() const noexcept + notify_all() noexcept { std::__atomic_notify_address(&_M_i, true); } #endif // __cpp_lib_atomic_wait @@ -654,11 +654,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // TODO add const volatile overload void - notify_one() const noexcept + notify_one() noexcept { _M_b.notify_one(); } void - notify_all() const noexcept + notify_all() noexcept { _M_b.notify_all(); } #endif // __cpp_lib_atomic_wait @@ -1434,12 +1434,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION template inline void - atomic_notify_one(const atomic<_Tp>* __a) noexcept + atomic_notify_one(atomic<_Tp>* __a) noexcept { __a->notify_one(); } template inline void - atomic_notify_all(const atomic<_Tp>* __a) noexcept + atomic_notify_all(atomic<_Tp>* __a) noexcept { __a->notify_all(); } #endif // __cpp_lib_atomic_wait diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/102994.cc b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/102994.cc index 9d92ff9..f572ce7 100644 --- a/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/102994.cc +++ b/libstdc++-v3/testsuite/29_atomics/atomic/wait_notify/102994.cc @@ -5,13 +5,13 @@ #include void -test1(const std::atomic& a, char* p) +test1(std::atomic& a, char* p) { a.wait(p); } void -test2(const std::atomic* a, int v) +test2(std::atomic* a, int v) { std::atomic_wait(a, v); std::atomic_notify_one(a); -- 2.7.4