[Bug libstdc++/39909] non-TLS version of std::call_once causes terminate

["jwakely dot gcc at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #2 from jwakely dot gcc at gmail dot com  2009-04-26 17:40 -------
Created an attachment (id=17707)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17707&action=view)
fix call_once without breaking ABI

Fix call_once to not use the global lock object, but retain the global for ABI
reasons.

__once_proxy detects if it was called by new code that provides the address of
a local lock object, or by old code that uses the global lock.

Without that check any uses of call_once inlined in old objects will be liable
to deadlock (because the global lock won't be unlocked before invoking the
functor) or segfaults (if the pointer is null when __once_proxy uses it).

Multiple concurrent calls to call_once from old object code will still
terminate, but it should be OK for new object code to use call_once freely, and
even for exactly one thread using the old call_once to run concurrently with
new code using call_once (because there would only be the single thread using
the global lock object.)

This patch adds the new symbols to the GLIBCXX_3.4.11 version but they should
be in a new 3.4.12 block - I don't know what I need to do for that.

Tested x86_64/linux --disable-tls


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39909