[patch libstdc++] Add POSIX variant of shared_timed_mutex.

[Jonathan Wakely]

On 16/01/15 14:12 +0100, Torvald Riegel wrote:
>[Resend.  Sorry for the noise on gcc@.]
>
>This adds a POSIX-based implementation of shared_timed_mutex, using
>pthread_rwlock_* operations directly instead of implementing with
>mutexes and two condvars.  This enables using an optimized
>pthread_rwlock_t on POSIX.
>
>Tested on x86_64-linux.
>
>OK?

OK for trunk - thanks.

>diff --git a/libstdc++-v3/include/std/shared_mutex b/libstdc++-v3/include/std/shared_mutex
>index 8bfede3..643768c 100644
>--- a/libstdc++-v3/include/std/shared_mutex
>+++ b/libstdc++-v3/include/std/shared_mutex
>@@ -57,6 +57,188 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>   /// shared_timed_mutex
>   class shared_timed_mutex
>   {
>+#if defined(__GTHREADS_CXX0X)

N.B. I advised Torvald that this macro was OK to check that we have
pthread_rwlock_t available. It's not strictly correct, but currently
only gthr-posix.h defines __GTHREADS_CXX0X so it works in practice. We
should come up with something better at a later date though, or if any
other gthreads model ever supports C++11 threads.