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For the case where a timeout is specified using the system_clock we perform a conversion to the preferred clock (which is either steady_clock or system_clock itself), wait using __cond_wait_until_impl, and then check the time by that clock again to see if it was reached. This is entirely redundant, as we can just call __cond_wait_until_impl directly. It will wait using the specified clock, and there's no need to check the time twice. For the no_timeout case this removes two unnecessary calls to the clock's now() function, and for the timeout case it removes three calls. libstdc++-v3/ChangeLog: * include/bits/atomic_timed_wait.h (__cond_wait_until): Do not perform redundant conversions to the same clock.
file: libstdc++-v3/README New users may wish to point their web browsers to the file index.html in the 'doc/html' subdirectory. It contains brief building instructions and notes on how to configure the library in interesting ways.