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[Bug nptl/14304] New: Provide some parts of librt in libc as well

             Bug #: 14304
           Summary: Provide some parts of librt in libc as well
           Product: glibc
           Version: 2.13
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: nptl
    Classification: Unclassified

librt links against libpthread, mostly because aio_* are implemented in threads
instead of in the kernel AFAICT.  This is unfortunate, because many libraries
would like to use (for example) clock_gettime, but doing so pulls in pthreads. 
Now you have no choice but to hit the more expensive thread-safe paths, because
your library can't know whether multiple threads actually exist, only whether
the pthread symbols are non-zero.

The complementary problem also exists for applications that are unthreaded: if
they link against librt, pthread symbols will be non-zero, and any thread-safe
library beneath that app now has to behave thread-safely.

This is especially comic when reading the clock_gettime implementation, which
goes out of its way to work correctly regardless of whether
__pthread_clock_gettime is available.

Ideally it would be possible to provide most of these symbols from libc
directly (presumably versioned so the app requires a sufficiently new libc).

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