#3016 Interp limit functionality with vwait call

[Anonymous]

It seems that vwait will not break when timeout
limit is hit. The following script does not stop:

set testvar ""
interp limit {} time -seconds 5
vwait testvar

[Nobody/Anonymous]

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Small addition - first time this problem appeared when I
tryed to break script execution from C code by setting
further execution time to one second - result was the
same.
P.S. Probably it would be handy to have
"Tcl_SetLimitExceeded" to break executing script

nyrl@mail.ru

[Donal K. Fellows]

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user_id=79902

Yeah, I've known about this issue for a while. Not sure how
to fix it yet though.

[Donal K. Fellows]

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user_id=79902

Examining what I've done so far, setting up a no-action
timer with Tcl_CreateTimerHandler will be sufficient; that
can be done at the same time as the creation of the time limit.

[Nobody/Anonymous]

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This doesn't seems to work, TimerHandler call doesn't
seems to activate timeout check even with time
granularity 1. Possible further problems - there are cases
when timeout limit check is called too rarely, so it can be
handy to force such a check each second. Imho, this can
be done by changing waiting loops (Tcl_Sleep and
Tcl_DoEvent) to do a limited wait, calling Tcl_CheckLimits
from time to time without checking time granularity.

Also I've found a small bug with time limits.
Tcl_SetTimeLimit sets relative timeout while
Tcl_CheckLimits check absolute timeout. Changes in
Tcl_SetTimeLimit like
Tcl_GetTime(&now);
usec = iPtr->limit.time.usec + now.usec;
iPtr->limit.time.sec += now.sec + usec / 1000000;
iPtr->limit.time.usec = usec % 1000000;
iPtr->limit.exceeded &= ~TCL_LIMIT_COMMANDS;
works, but when You call
puts "Limit is: [ interp limit {} time ]"
from script You'll get absolute timeouts, what can be
misguiding.

nyrl@mail.ru

[Donal K. Fellows]

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There was a minor error (wrong comparison operator!) in the
time limit evaluation code that made it postpone enforcing
the limit until the end of the second. :^}

Fixing blocking [after] is unpleasant, but fairly
straight-forward.

Fixing blocking [exec] (or other blocking IO) is beyond what
I understand how to do at the moment. :^(

[Donal K. Fellows]

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user_id=79902

Fixed [vwait], [update] and [after <num>] to be time-limit
aware.

The fix for [vwait] and [update] is elegant (a timer event
that checks the limit at the time when the limit is expected
to be exceeded) and the fix for blocking [after] is not
(fragment the blocking wait!) but all cases should now work.

Thanks for reporting this!