Evgeniy Polyakov wrote:
One can set number of events before the syscall and do not remove them
after syscall. It can be updated if there is need for that.
Nobody doubts that it is possible. But it is
a) potentially much expensive
and
b) an alien concept
to have the signal mask to set during the wait call implicitly.
Conceptually it doesn't even make sense. This is no event to wait for.
It a parameter for the specific wait call, just like the timeout. And
I fortunately haven't seen you proposing to pass the timeout value
implicitly.
Not good enough? It does exactly what it is supposed to do. What can
there be "not good enough"?
Not to move signals into special case of events. If poll() can not work
with them it does not mean, that they need to be specified as additional
syscall parameter, instead change poll() to work with them, which can be
easily done with kevents.
You still seem to be completely missing the point. The signal mask is
no event to wait for. It has nothing to do with this that ppoll() takes
the signal mask as a parameter. The signal mask is a parameter for the
wait call just like the timeout, not more and not less.
Do not mix warm and soft - waiting for some period is not equal to
syscall timeout. Waiting is possible with timer kevent user (although
only relative timeout, can be changed to support both, not a big
problem).
That's what I'm saying all the time. Of course it can be supported.
But for this the timeout parameter must be a timespec pointer. Whatever
you could possibly mean by "do not mix warm and soft" I cannot possibly
imagine. Fact is that both relative and absolute timeouts are useful.
And that for absolute timeouts the change of the clock has to be taken
into account.
I'm quite sure that absolute timeouts are very usefull, but not as in
the case of waiting for syscall completeness. In any way, kevent can be
extended to support absolute timeouts in it's timer notifications.
That's not the same. If you argue that then the syscall should have no
timeout parameter at all. Fact is that setting up a timer is not for
free. Since the timeout is used all the time having a timeout parameter
is the right answer. And if you do this then do it right just like
every other syscall other than poll: use a timespec object. This gives
flexibility without measurable cost.
--
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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