Aaron Graham <aaron@aarongraham.com> writes:
When condition::wait_until is called with a monotonic_clock time_point, that time_point is translated to a system_clock time_point. If the system_clock is changed (via NTP, adjtime, settimeofday, etc) between when convert_to<system_clock> is called and when the underlying posix call is made, the very reason for using monotonic_clock defenestrates and splatters all over the pavement. Depending on the magnitude of the clock change, wait_until could hang forever.
That is a problem with the implementation of condition_variable::wait_until rather than monotonic_clock. My commercial Just::Thread library provides an implementation of std::condition_variable that works correctly with both monotonic_clock and system_clock on Linux and Windows. It does rely on recent versions of the linux kernel though (>=2.6.19 IIRC). The boost::condition_variable implementation is a wrapper around pthread_cond_wait, and will continue to have difficulties with using different clocks --- you can either do all waits on the monotonic clock (assuming there is one) or all waits on the system clock. Anything else has to convert. Anthony -- Author of C++ Concurrency in Action http://www.stdthread.co.uk/book/ just::thread C++0x thread library http://www.stdthread.co.uk Just Software Solutions Ltd http://www.justsoftwaresolutions.co.uk 15 Carrallack Mews, St Just, Cornwall, TR19 7UL, UK. Company No. 5478976