On Tue, 2 Mar 2010, Henrik Sperre Johansen wrote:
PS. For the not-so-faint-of-heart, open a Transcript and try evaluating: |proc| proc := [[Transcript show: 'Start!'. ] ensure: [Transcript show: 'Finish!' Processor yield.]] newProcess. proc resume. Processor yield. proc suspend. proc terminate. Why don't we get it printing? Forgot a . there, supposed to be
|proc| proc := [[Transcript show: 'Start!'. ] ensure: [Transcript show: 'Finish!'. Processor yield.]] newProcess. proc resume. Processor yield. proc suspend. proc terminate.
on my machine it prints: *Start!Start!Finish!
The problem occurs because Transcript >> #endEntry (sent from #show:) takes a while to execute, so the process (proc) prints 'Start!', but it gets terminated before execution reaches #resetContents (#reset in Squeak). So 'Start!' is still in the stream. Then our process executes the #ensure: block and it prints 'Start!' and 'Finish!' too. There's worse problem with #ensure: and #terminate is that, a process executing an #ensure: block can be terminated. If you evaluate this code: | process stage1 stage2 stage3 counter | stage1 := stage2 := stage3 := false. counter := 0. process := [ [ stage1 := true ] ensure: [ stage2 := true. 1000000 timesRepeat: [ counter := counter + 1 ]. stage3 := true ] ] newProcess. process resume. Processor yield. process suspend. process terminate. 1000 milliSeconds asDelay wait. { stage1. stage2. stage3. counter } explore you will find that stage1 and stage2 is reached as expected, but stage3 is not and counter is less than 1000000. That's because the forked process started evaluating the #ensure: block, but it was terminated by our process. Is this the expected behavior when sending #terminate to a process which is evaluating an #ensure: block? Cheers, Balázs & Levente
*yay Henry* *