Re: repeat(0)/repeat(1) and stop()/start()

On Mon, Feb 21, 2000 at 11:24:45AM +0100, [email protected] wrote:
> I was talking with another programmer about Event, and we came to a
> point where he asked me if repeat(0)/repeat(1) is synonym to
> stop()/start(). This seems to be underdocumented, so I wrote this hack
> [... snip ...]
> 
> This script implements a one shot watcher which is activated and
> deactivated by several timers via repeat(). Some thoughts:
> 
> Until this question, I expected that a one shot watcher automatically
> becomes INACTIVE after callback invokation. But if you run the script,
> you can see that the repeat() method surprisingly does not influence the
> activity flag EVEN AFTER CALLBACK INVOKATION.

Try the attached script.  If you type something while REPEAT=1 then the
watcher remains active.  However, if you type something while REPEAT=0
then the watcher changes to inactive, permanently.  I think this is
correct...?

> So we have an active
> watcher behaving like an inactive one after callback invokation. If you
> observe such a watcher by ProcessTop, it is reported as "zombie", but as
> the programmer proposed, different to usual zombies it can be reanimated
> by a call of repeat(1).

The watcher can be reanimated by calling start() or again().  Try typing
start or again in the test script.

> So, to sum it up, thanks to this proposal I discovered this unexpected
> usage of the repeat() method. My question is if it is necessary to
> implement it that hidden way - there seems to exist an additional
> internal flag. Wouldn't it make the interface clearer if repeat(0) would
> enforce a watcher to become simply INACTIVE after callback invokation?
> This would allow to reuse the watcher later on by simply calling again()
> - for just another one shot activity (the repeat attribute would remain
> unchanged). repeat(1), on the other hand, should just set the attribute
> in my opinion, as well as other attribute methods do. It should not
> reactivate the watcher.

I don't understand.

> Just another point. The script above runs well on Solaris, but on Linux
> it behaves differently. If you enter something in STDIN on Linux while
> the script reports to be "INACTIVE", the screen is filled by a message
> that an event arrived for an "!ACTIVE" watcher. This message is
> displayed again and again, and it seems the loop is out of control then,
> no callback is invoked after this.

Can you post the output?  This sounds like a real bug...

-- 
"May the best description of competition prevail."
          via, but not speaking for Deutsche Bank