Semaphores and queue together. Is it necessary?

Hello.
I am using a State Machine driven by queue, using a For Loop to enqueue three States that have to be executed in sequence. The code is working fine but when I run it in Highlight Mode is possible to see that the "State 1" of the State Machine start running while the For Loop (which enqueue the elements) is still running. Is this kind of code safe?
I mean, for this example everything is working fine, but if I have SubVIs running in the States of the State Machine, would not be safer to have the For Loop execution done, before start playing with the SubVIs of the State Machine? Would a semaphore help me with that? I found this thread that discussed similar things, but I still thing that would be safer to have the For Loop done and just after that start running the State Machine.
What do you thing guys?
Thanks
Dan07
Message Edited by dan07 on 04-17-2010 02:59 AM
Attachments:
Enqueue.vi ‏16 KB

Good question dan!
The code you are explaining is "SAFE". and seems like a good implementation of a basic "Producer-comsumer archetecture" Your UI stays responsive while the consumer loop does all the data manipilations. A very positive point.
I am a bit concerned about scaleability of the code since you have added a programatic "flush queue" in the consumer loop. It does what you want today but, what if you add a state that enters from another event? the flush queue tosses that element out too. and you might really want to do what the operator asked. I would do the time check in the producer loop (not much code to slow things down - just a timer call and a comparison right?) and determine if its correct to queue up the time based state(s).
Then again- I'm struck with the need for a time enabled state- will the operator expect the code to behave differently at different times? It is possible but, questionable.
By-the way.
you can exit the consumer loop based on the error out of the dequeue element. it returns when the queue is destroyed or when there is an element.
Message Edited by Jeff Bohrer on 04-17-2010 03:39 PM
Message Edited by Jeff Bohrer on 04-17-2010 03:41 PM
Jeff

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When do VI and queue references become invalid?

Hi all,
I have a fairly complicated problem, so please bear with me.
1) I have a reentrant SubVI (let's call it VI "Assign") that has an input cluster of (VI ref, queue ref) (let's call the cluster type "Refs"). If the VI ref is invalid (first execution), the VI ref and queue ref are assigned values and are passed on as an output cluster of same type. (The VI does other things too, but for simplicity only this is important.)
2) The VI that calls VI "Assign" (let's call it VI "Store") is not reentrant and has a local variable of type "Refs" that is wired to the input and output of VI "Assign". This VI effectively stores the references. The references returned by VI "Assign" are always valid right after the call, but after the problem condition described below, they are invalid at the start of all calls before they are passed to VI "Assign".
3) VI "Store" is called by multiple non-reentrant VIs, so the local variables of VI "Assign" retain their values (Has been tested and verified to retain their values). The VI causing the problem in this case is a template VI of which multiple copies are launched (let's call it VI "Template").
The problem is that the moment an instance of VI "Template" is closed, the queue reference becomes invalid, although the actual variant value of the reference remains the same. The VI ref can become invalid or not, depending on small changes, but is always reproducible. I assume there must be some similarity between VI and queue refs. After spending some time researching, the Labview help states for the Open VI Ref component "If you do not close this reference, it closes automatically after the top-level VI associated with this function executes." In this case I assumed it means that the moment the reentrant VI "Assign" finishes, the references will get cleared ?? So I made a non-reentrant VI (let's call it VI "NR Assign") that only assigns values to the references and VI "Assign" now calls this VI (It effectively does what I described VI "Assign" does). I keep this VI alive by using it in a VI which never terminates and since it never terminates, the references should never become invalid. Anyone still following? This didn't solve the problem though. If I reproduce the same scenario using only one instance of the template VI, it works just fine. Furthermore, the VI and queue references are never closed, to aid analysis of the problem. Can anyone shine some light on what happens when a template VI terminates? Could this be the problem?
Unfortunately I cannot include the code.
Thank you whoever is able to make sense of this.
Christie

Christie wrote:
Hi all,
I have a fairly complicated problem, so please bear with me.
1) I have a reentrant SubVI (let's call it VI "Assign") that has an input cluster of (VI ref, queue ref) (let's call the cluster type "Refs"). If the VI ref is invalid (first execution), the VI ref and queue ref are assigned values and are passed on as an output cluster of same type. (The VI does other things too, but for simplicity only this is important.)
2) The VI that calls VI "Assign" (let's call it VI "Store") is not reentrant and has a local variable of type "Refs" that is wired to the input and output of VI "Assign". This VI effectively stores the references. The references returned by VI "Assign" are always valid right after the call, but after the problem condition described below, they are invalid at the start of all calls before they are passed to VI "Assign".
3) VI "Store" is called by multiple non-reentrant VIs, so the local variables of VI "Assign" retain their values (Has been tested and verified to retain their values). The VI causing the problem in this case is a template VI of which multiple copies are launched (let's call it VI "Template").
The problem is that the moment an instance of VI "Template" is closed, the queue reference becomes invalid, although the actual variant value of the reference remains the same. The VI ref can become invalid or not, depending on small changes, but is always reproducible. I assume there must be some similarity between VI and queue refs. After spending some time researching, the Labview help states for the Open VI Ref component "If you do not close this reference, it closes automatically after the top-level VI associated with this function executes." In this case I assumed it means that the moment the reentrant VI "Assign" finishes, the references will get cleared ?? So I made a non-reentrant VI (let's call it VI "NR Assign") that only assigns values to the references and VI "Assign" now calls this VI (It effectively does what I described VI "Assign" does). I keep this VI alive by using it in a VI which never terminates and since it never terminates, the references should never become invalid. Anyone still following? This didn't solve the problem though. If I reproduce the same scenario using only one instance of the template VI, it works just fine. Furthermore, the VI and queue references are never closed, to aid analysis of the problem. Can anyone shine some light on what happens when a template VI terminates? Could this be the problem?
Unfortunately I cannot include the code.
Thank you whoever is able to make sense of this.
Christie
All LabVIEW refnums do get deallocated automatically when the top-level VI in whose hierarchy the refnum was created goes idle (stops executing). You will have to make sure that the creation of a refnum is done inside a VI hierarchy that stays running for the entire time you want to use that refnum.
Rolf Kalbermatter
Message Edited by rolfk on 06-27-2007 11:52 AM
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

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Hi
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sky00ber wrote:
Hi,
What is required in the HOST and QUEUE field when setting a WIFI printer?
When setting up my printer, i fill the options identical to what follows:
PRINTER: SAMSUNG HOME
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if it helps, my printer is SAMSUNG CLX-3175FW. It is Wifi Enable and is connected to my HOME acces point.
please do correct me if there has to be changes to the BEARER or anything else.
HELP URGENTLY NEEDED!
I'm not sure but I give it a try.Turn your security(WPA/WEP) and Firewall temporarely off. HOST is the IP address of the printer. QUEUE can be YES or a specific amount of prints, like 1,2,3......
If I look at the manual of your printer I see that you can find the IP and MAC addresses in the Network Configuration Report.I don't know what the USER is doing there because if there is a user then there must be a password.
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Semaphores and queue together. Is it necessary?

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