In article <[EMAIL PROTECTED]>, David L. Mills <[EMAIL PROTECTED]> wrote: >I don't understand how POSIX can implement a time of day function using >timers.
It does precisely the opposite: timers are implemented in terms of the TOD. Here's what the standard says: # Each implementation shall define a set of clocks that can be used as # timing bases for per-process timers. All implementations shall # support a clock_id of CLOCK_REALTIME. If the Monotonic Clock option # is supported, implementations shall support a clock_id of # CLOCK_MONOTONIC. (timer_create, XSI6 page 1514, IEEE Std.1003.1-2001) # If the flag TIMER_ABSTIME is set in the argument flags, # timer_settime( ) shall behave as if the time until next expiration # is set to be equal to the difference between the absolute time # specified by the it_value member of value and the current value of # the clock associated with timerid. That is, the timer shall expire # when the clock reaches the value specified by the it_value member of # value. (timer_getoverrun [sic], XSI6 page 1518, IEEE Std.1003.1-2001) # If the value of the CLOCK_REALTIME clock is set via clock_settime( ), # the new value of the clock shall be used to determine the time of # expiration for absolute time services based upon the CLOCK_REALTIME # clock. This applies to the time at which armed absolute timers # expire. If the absolute time requested at the invocation of such a # time service is before the new value of the clock, the time service # shall expire immediately as if the clock had reached the requested # time normally. # Setting the value of the CLOCK_REALTIME clock via clock_settime( ) # shall have no effect on threads that are blocked waiting for a # relative time service based upon this clock, including the # nanosleep( ) function; nor on the expiration of relative timers # based upon this clock. Consequently, these time services shall # expire when the requested relative interval elapses, independently # of the new or old value of the clock. (clock_getres [sic], XSI6 page 195, IEEE Std.1003.1-2001) -GAWollman -- Garrett A. Wollman | As the Constitution endures, persons in every [EMAIL PROTECTED] | generation can invoke its principles in their own Opinions not those | search for greater freedom. of MIT or CSAIL. | - A. Kennedy, Lawrence v. Texas, 539 U.S. 558 (2003) _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
