From: Jonathan Wakely <jwakely@redhat.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>,
libstdc++@gcc.gnu.org,
Alexander Potapenko <glider@google.com>,
Kostya Serebryany <kcc@google.com>,
Torvald Riegel <triegel@redhat.com>
Subject: Re: [Patch, libstdc++] Fix data races in basic_string implementation
Date: Tue, 01 Sep 2015 15:08:00 -0000 [thread overview]
Message-ID: <20150901150847.GH2631@redhat.com> (raw)
In-Reply-To: <CACT4Y+YTP1SOU-U8E=rxZccHkQTOFAXHgZg6-YZ2tSvsgxfifQ@mail.gmail.com>
On 01/09/15 16:56 +0200, Dmitry Vyukov wrote:
>I don't understand how a new gcc may not support __atomic builtins on
>ints. How it is even possible? That's a portable API provided by
>recent gcc's...
The built-in function is always defined, but it might expand to a call
to an external function in libatomic, and it would be a regression for
code using std::string to start requiring libatomic (although maybe it
would be necessary if it's the only way to make the code correct).
I don't know if there are any targets that define __GTHREADS and also
don't support __atomic_load(int*, ...) without libatomic. If such
targets exist then adding a new configure check that only depends on
__atomic_load(int*, ...) would mean we keep supporting those targets.
Another option would be to simply do:
bool
_M_is_shared() const _GLIBCXX_NOEXCEPT
#if defined(__GTHREADS)
+ { return __atomic_load(&this->_M_refcount, __ATOMIC_ACQUIRE) > 0; }
+#else
{ return this->_M_refcount > 0; }
+#endif
and see if anyone complains!
next prev parent reply other threads:[~2015-09-01 15:08 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-01 12:52 Dmitry Vyukov
2015-09-01 14:27 ` Jonathan Wakely
2015-09-01 14:56 ` Dmitry Vyukov
2015-09-01 15:08 ` Jonathan Wakely [this message]
2015-09-01 15:42 ` Dmitry Vyukov
2015-09-02 13:17 ` Jonathan Wakely
2015-09-02 14:02 ` Dmitry Vyukov
2015-09-02 14:08 ` Jonathan Wakely
2015-09-02 14:39 ` Dmitry Vyukov
2015-09-02 10:58 ` Marc Glisse
2015-09-02 13:50 ` Dmitry Vyukov
2015-09-02 14:05 ` Jonathan Wakely
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