On Mon, Sep 22, 2014 at 4:57 AM, Max Leske <maxleske@gmail.com> wrote:
Hi Eliot,
Thanks a lot for those explanations.
On 18.09.2014, at 20:53, Eliot Miranda <eliot.miranda@gmail.com> wrote:
Hi Max,
phhh, time zone differences suck ;-)
On Thu, Sep 18, 2014 at 3:50 AM, Max Leske <maxleske@gmail.com> wrote:
Hi Eliot,
On 18.09.2014, at 01:18, Eliot Miranda <eliot.miranda@gmail.com> wrote:
Hi Max,
On Wed, Sep 17, 2014 at 1:59 PM, Max Leske <maxleske@gmail.com> wrote:
Hi Eliot
On 16.09.2014, at 20:18, Eliot Miranda <eliot.miranda@gmail.com> wrote:
Hi Max,
On Tue, Sep 16, 2014 at 11:05 AM, Max Leske <maxleske@gmail.com> wrote:
Hi
As always when I want to check if a process has died I get very confused by #isTerminated and Iâm wondering if I just donât get how itâs supposed to work or if there are others that share my confusion.
Old implementation:
isTerminated
self isActiveProcess ifTrue: [^ false]. ^suspendedContext isNil or: ["If the suspendedContext is the bottomContext it is the block in Process>>newProcess. If so, and the pc is greater than the startpc, the bock has alrteady sent and returned from value and there is nothing more to do." suspendedContext isBottomContext and: [ suspendedContext pc > suspendedContext startpc ] ]
Pharo 4 implementation:
isTerminated self isActiveProcess ifTrue: [^ false]. ^suspendedContext isNil or: ["If the suspendedContext is the bottomContext it is the block in Process>>newProcess. If so, and the pc is greater than the startpc, the bock has alrteady sent and returned from value and there is nothing more to do.â suspendedContext isBottomContext and: [ suspendedContext isDead not â<âââââââââââââââââââââââââ new" and: [ suspendedContext pc > suspendedContext startpc ] ] ]
The old implementation would break if the suspended context was dead (i.e. the pc was nil) because the send of #> would produce an MNU. The new implementation doesnât fix that, even though it looks like it at first glance: if the pc is nil, the #> send will still happen -> MNU.
Off the top of my head it would seem that it should be isDead or: [] not isDead not and:
isTerminated self isActiveProcess ifTrue: [^ false]. ^suspendedContext isNil or: ["If the suspendedContext is the bottomContext it is the block in Process>>newProcess. If so, and the pc is greater than the startpc, the bock has alrteady sent and returned from value and there is nothing more to do.â suspendedContext isBottomContext and: [ suspendedContext isDead or: [ suspendedContext pc > suspendedContext startpc ] ] ]
Phew. Glad you see that the same way.
isDead
^ pc isNil
and maybe (suspendedContext pc ifNil: [true] ifNotNil: [:pc| pc > suspendedContext startpc]) is more obvious.
Anyway, neither implementation will reliably tell me if the process has
been terminated: - an inactive process will be suspended when #terminate is sent and report that it has not been terminated (#isSuspended -> true, #isTerminated -> false)
except that it *hasn't* been terminated, it is merely in the process of termination. It isn't terminated until all unwind blocks have run, right?
True. Easy to forget when you can just kill -9 on the console⦠:)
- a properly terminated process will raise an MNU (although apparently not always�)
but that's a bug the change I suggested will fix.
- all the states in between: no clue
I would like to know two things: 1. how can I check if a process has already *received* a #terminate? (I would then assume that the process will die eventually)
I don't think you can without putting a critical section around terminate and adding some process-specific variable that is set when you send terminate. termination is not instantaneous (unwind blocks have to be run), so it is potentially interruptible.
Iâve thought about this a bit. I wouldnât really care if I donât get a correct answer about the termination status immediately but I want to have it before the process terminates. In case of something like the following:
([ 10 seconds asDelay wait ] forkAt: 11) terminate
it can (potentially) take a very long time for the process to terminate. So if I have to poll 3 or 4 times thatâs ok but I donât want to wait for minutes. One solution would be to take your idea of the variable, but without the critical block:
terminate "Stop the process that the receiver represents forever. Unwind to execute pending ensure:/ifCurtailed: blocks before terminating."
| ctxt unwindBlock oldList | terminating := true. â<âââââââââââââââââââââââââââââââââââ changed" self isActiveProcess ifTrue: [ ctxt := thisContext. [ ctxt := ctxt findNextUnwindContextUpTo: nil. ctxt isNil ] whileFalse: [ (ctxt tempAt: 2) ifNil: [ ctxt tempAt: 2 put: nil. unwindBlock := ctxt tempAt: 1. thisContext terminateTo: ctxt. unwindBlock value ]]. thisContext terminateTo: nil. self suspend ] ifFalse: [ "Always suspend the process first so it doesn't accidentally get woken up" oldList := self suspend. suspendedContext ifNotNil:[ "Figure out if we are terminating the process while waiting in Semaphore>>critical: In this case, pop the suspendedContext so that we leave the ensure: block inside Semaphore>>critical: without signaling the semaphore." (oldList class == Semaphore and:[ suspendedContext method == (Semaphore compiledMethodAt: #critical:)]) ifTrue:[ suspendedContext := suspendedContext home.]. "If we are terminating a process halfways through an unwind, try to complete that unwind block first." (suspendedContext findNextUnwindContextUpTo: nil) ifNotNil: [ :outer | (suspendedContext findContextSuchThat: [ :c | c closure == (outer tempAt: 1)]) ifNotNil: [ :inner | "This is an unwind block currently under evaluation" suspendedContext runUntilErrorOrReturnFrom: inner ]]. ctxt := self popTo: suspendedContext bottomContext. ctxt == suspendedContext bottomContext ifFalse: [ self debug: ctxt title: 'Unwind error during termination']] ].
isTerminating ^ terminating ifNil: [ ^ false ]
With this small modification I can run the example from above and immediately see that it will die eventually.
Iâm aware that one process might not see the change to the variable immediately but as I said, I wouldnât really care.
What do you think?
Yes that looks good. But given that branches are atomic (ifTrue: is not a send) why not do
Process>>initialize terminating := false.
terminate "Stop the process that the receiver represents forever. Unwind to execute pending ensure:/ifCurtailed: blocks before terminating."
| ctxt unwindBlock oldList | terminating ifTrue: [self error: 'Process is already terminated, or being terminated'] ifFalse: [terminating := true]. self isActiveProcess ifTrue: ...
?
I would suggest a status inst var, as in
Process>>initialize status := nil
terminate "Stop the process that the receiver represents forever. Unwind to execute pending ensure:/ifCurtailed: blocks before terminating."
| ctxt unwindBlock oldList | status == #terminating ifTrue: [self error: 'Process is already terminated, or being terminated'] ifFalse: [status := terminating]. self isActiveProcess ifTrue: ...
but the temptation then is to have lots of different status values and I'm leery of introducing that kind of complication without a strong justification.
Iâve worked a bit on an implementation along your suggestions. I wrote a test which looks like this:
testIsTerminated | proc | proc := [ Semaphore new wait ] forkAt: 30. self deny: proc isSuspended. self deny: proc isTerminating. self deny: proc isTerminated. proc terminate. self deny: proc isTerminated. self assert: proc isSuspended. self assert: proc isTerminating. [ proc isTerminated ] whileFalse: [ 1 second asDelay wait ]. â<âââââââââââ ???"
self assert: proc isTerminated. self assert: proc isTerminating
The test works AFAICT (apart from the loopâ¦) but I want to also have a check after the process has terminated. Is there some reliable way to wait for a process to die? I tried something like this for example:
proc run. self assert: proc isTerminated.
But that locks up the active process (obviously) until I interrupt it manually. If there is such a way, I could also add a method that lets a process x wait for the completion of a process y for example (or not, depending on how difficult it is :) )
I can't see anything to do other than waiting. One thing is to run the process at as close to user priority as possible, so I would say
proc := [ Semaphore new wait ] forkAt: Processor activePriority - 1.
Another important thing is that you're not giving your process a chance to run before you test for it not terminating. So adding a yield after the first set of asserts and then repeating them is good:
started := false. proc := [ started := true. Semaphore new wait ] forkAt: 30. self deny: proc isSuspended. self deny: proc isTerminating. self deny: proc isTerminated. (Delay forMilliseconds: 10) wait. self assert: started. self deny: proc isSuspended. self deny: proc isTerminating. self deny: proc isTerminated.
Another thing might be to boost its priority to make sure it finishes (except that that'll probably have no effect because IIRC right now the terminator runs the termination). So you could say
proc terminate. self deny: proc isTerminated. self assert: proc isSuspended. self assert: proc isTerminating.
process priority: Processor activePriority + 1. [ proc isTerminated ] whileFalse: [ 1 second asDelay wait ].
Further I'd want to test that unwind blocks have been run so I'd say
testIsTerminated | proc started unwound terminator | unwound := false. proc := [ started := true. [Semaphore new wait] ensure: [terminator := Processor activeProcess. unwound := true] ] forkAt: Processor activePriority - 1. self deny: proc isSuspended. self deny: proc isTerminating. self deny: proc isTerminated. (Delay forMilliseconds: 10) wait. "Alloc proc to run; there shouldnt be too much else going on so this delay should suffice"
self assert: started. self deny: proc isSuspended. self deny: proc isTerminating. self deny: proc isTerminated. proc terminate. proc priority: Processor activePriority + 1. "This may have no effect; termination may be executed by the terminator rather than the terminatee; ys, this is a bug" self deny: proc isTerminated. self assert: proc isSuspended. self assert: proc isTerminating. (Delay forMilliseconds: 10) wait. "Allow proc to terminate; there shouldnt be too much else going on so this delay should suffice"
self assert: proc isTerminated. self assert: proc isTerminating. self assert: unwound. self assert: terminator == proc. "But this should be made an expected failure; I don't know how to do that in SUnitâ¦"
From your comments I expected this last statement to fail but actually it doesnât. I guess thatâs a good sign (?).
Yes, that's great!
and google's mail text editor *SUCKS*!!!!
lol :p
I spent so much time editing the code in the message with the editor doing weird things like pasting the fragment I was appending to a line to the end of the previous line, etc. Drove me *mad* :-) I noticed something else regarding terminated processes that have never run
and Iâm not sure if thatâs not a bug: When I suspend a process (that has never run) that is not the active process, I can reliably reproduce that the entire #terminate method is being executed. The processâ suspendedContext is the bottom context (as it should be). However, the pc is equal to the startpc, since that process never had a chance to to anything. The result is that #isTerminated will answer false, even though the process is technically terminated.
Hmmm. You might want to add code to #terminated to check for that case, and set the pc to endPC + 1, or nil. Just make sure there's a comment ;-)
One side effect of this is that itâs impossible to do something like â[ proc isTerminated ] whileFalse: [ 1 second asDelay wait ].â because that will not terminate for all processes. Luckily those processes can be garbage collected regardless of what #isTerminated says.
Right.
One obvious fix would be to set the pc of the suspendedContext to nil but Iâm not sure thatâs a good idea.
What do you think?
Cheers, Max
Cheers,
Max
Cheers,
Max
2. how can I check if a process is *actually* dead? (in case a âhalf
deadâ process will still unwind or whatever)
see above.
What would be necessary to make those tests (or better ones) possible
(rewrite the whole process implementation?)?
Cheers, Max
-- best, Eliot
-- best, Eliot
-- best, Eliot
--
best, Eliot