[patch] libstdc++/64847 add autoconf checks for pthread_rwlock_t

[Jonathan Wakely]

On 13/03/15 13:46 +0000, Jonathan Wakely wrote:
>On 12/03/15 18:49 +0000, Jonathan Wakely wrote:
>>I assumed that Pthreads was enough to ensure pthread_rwlock_t but
>>https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64847 shows that isn't
>>true for HPUX (seems it was optional prior to POSIX 1003.1-2001).
>>
>>This adds an autoconf check to decide whether to use pthread_rwlock_t
>>or the fallback implementation in terms of std::condition_variable and
>>std::mutex.
>
>Actually the autoconf changes aren't needed, as PR 64847 is already
>fixed. Maybe it's better to have an explicit check for
>pthread_rwlock_t anyway though ... I'll have a think.

Here's what I've committed, it has Torvald's fixes for retrying on
EAGAIN, lengthy comments explaining why we retry, and also the
autoconf macros (as having a _GLIBCXX_USE_PTHREAD_RWLOCK_T macro that
can be explicitly overriden in a per-target c++config.h is probably
useful).

Tested x86_64-linux, committed to trunk.
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