Re: [boost] [thread] monotonic xtime

From: Kim Barrett (kab_at_[hidden])
Date: 2006-04-10 21:31:13

At 6:37 PM +0200 4/10/06, Ulrich Eckhardt wrote:
>Hi!
>
>An application I'm writing has the special requirement that it be able to
>handle time-skews gracefully (like e.g. the daylight saving time or a user
>changing the system time). [...]
>
>However, I noticed that this won't work, because things like thread::sleep()
>implicitly assume that the given time is from TIME_UTC and also only uses
>that one to compare against [...]

Regrettably, good monotonic clock support seems to be weak at both the
standards level and in actual implementations. Since boost.thread is
largely a portable wrapper around the underlying OS-specific facilities,
that probably makes it rather difficult for boost.thread to do better.

>On a related note, why doesn't the threading lib offer any means to yield for
>a certain time? In more than nine out of ten cases, this is the way I do
>things, waiting for a certain point in time - like Boost.Thread does - is
>rather the exception than the rule.

Because a user can easily synthesize a relative time measuer on top of an
interface that uses absolute times, but there is a race condition associated
with a user attempting to specify an absolute timeout on top of an interface
that uses relative timeouts.  See, for example, the Rationale section for
pthread_cond_timedwait() in the Single Unix Specification for more details.