On Nov 26 10:47, James E. King III wrote: > On Mon, Nov 26, 2018 at 10:35 AM Corinna Vinschen > wrote: > > > > On Nov 25 09:01, James E. King III wrote: > > > I have isolated a problem in pthread_cond_timedwait when the condattr > > > is used to set the clock type to CLOCK_MONOTONIC. In this case even > > > though a target time point in the future is specified, the call > > > returns ETIMEDOUT but a subsequent call to > > > clock_gettime(CLOCK_MONOTONIC) shows the desired time point was not > > > reached. > > > > > > $ gcc timed_wait_short.c -o timed_wait_short > > > $ ./timed_wait_short.exe > > > [...] > > > begin: 521056s 671907500n > > > target: 521056s 721907500n > > > end: 521056s 721578000n > > > ok: false > > > > > > I have attached the source code. > > > > Thanks for the testcase. The problem is this: > > [...] > > At the moment I only have an *ugly* idea: We can always add the > > coarsest resolution of the wait functions (typically 15.625 ms) to the > > relative timeout value computed from the absolute timeout given to > > pthread_cond_timedwait. In my testing this is sufficient since the > > difference between target and actual end time is always < 15ms, in > > thousands of runs. > > > > Thoughts? > > > > > > Thanks, > > Corinna > > > > (*) https://docs.microsoft.com/en-us/windows/desktop/Sync/wait-functions#wait-functions-and-time-out-intervals > > > > -- > > Corinna Vinschen > > Cygwin Maintainer > > Some thoughts: > > https://cygwin.com/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=winsup/cygwin/thread.cc;h=0bddaf345d255ae39187458dc6d02b1b4c8087c1;hb=HEAD#l2546 > > In pthread_convert_abstime, line 2564, care is taken to adjust for > rounding errors. > At line 2574, the rounding is not accounted for when adjusting for a > relative wait because it is a monotonic clock. > Wouldn't that rounding error cause it to wait less time? Au contraire: - The end time you're waiting for is rounded *up*. - The current time is rounded *down* - So end time - current time is always bigger than required on the 100ns level. Make sense? Corinna -- Corinna Vinschen Cygwin Maintainer