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:     521036s  122315900n
target:     521036s  172315900n
   end:     521036s  173293100n
    ok: true
 begin:     521036s  174872400n
target:     521036s  224872400n
   end:     521036s  224378900n
    ok: false
Jim@pulsar /cygdrive/c/users/jim/desktop
$ ./timed_wait_short.exe
 begin:     521052s   95953200n
target:     521052s  145953200n
   end:     521052s  145284000n
    ok: false
Jim@pulsar /cygdrive/c/users/jim/desktop
$ ./timed_wait_short.exe
 begin:     521056s  396277200n
target:     521056s  446277200n
   end:     521056s  446664700n
    ok: true
 begin:     521056s  454535100n
target:     521056s  504535100n
   end:     521056s  504567000n
    ok: true
 begin:     521056s  510360800n
target:     521056s  560360800n
   end:     521056s  560555600n
    ok: true
 begin:     521056s  566604400n
target:     521056s  616604400n
   end:     521056s  616622800n
    ok: true
 begin:     521056s  619277800n
target:     521056s  669277800n
   end:     521056s  669646400n
    ok: true
 begin:     521056s  671907500n
target:     521056s  721907500n
   end:     521056s  721578000n
    ok: false

I have attached the source code.

Cygwin DLL version info:
        DLL version: 2.11.2
        DLL epoch: 19
        DLL old termios: 5
        DLL malloc env: 28
        Cygwin conv: 181
        API major: 0
        API minor: 329
        Shared data: 5
        DLL identifier: cygwin1
        Mount registry: 3
        Cygwin registry name: Cygwin
        Installations name: Installations
        Cygdrive default prefix:
        Build date:
        Shared id: cygwin1S5