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Subject: [Bug libstdc++/102994] std::atomic<ptr>::wait is not marked const
Date: Fri, 22 Apr 2022 22:54:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102994

--- Comment #17 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Thomas Rodgers
<rodgertq@gcc.gnu.org>:

https://gcc.gnu.org/g:977cbabeb1c1a9a28cc45655bdc693e1594642f0

commit r11-9931-g977cbabeb1c1a9a28cc45655bdc693e1594642f0
Author: Thomas W Rodgers <trodgers@redhat.com>
Date:   Fri Apr 22 15:46:19 2022 -0700

    libstdc++: Make atomic notify_one and notify_all non-const

    <recording this here for future reference>
    PR102994 "atomics: std::atomic<ptr>::wait is not marked const" raises t=
he
    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 h=
ard
    to conceive of a desirable implementation approach that would require i=
t).
    The original paper proposing the wait/notify functionality for atomics
    (p1185) also had these members marked const for the first three revisio=
ns,
    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<bool>::notify_one, notify_all):
            Likewise.
            (atomic::notify_one, notify_all): Likewise.
            (atomic<T*>::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.

    (cherry picked from commit 7c21556daf385fe9ece37319f574776dd7d8ab1c)=