publish subscriber

Eugen Graf · May 8, 2007

Have anybody been worked with "publish subscriber" methode? Any informations?

Thanks, Eugen

Michael Aivaliotis · May 9, 2007

Are you referring to a specific vi server method or the general concept of publish/subscribe?

I would think that if you create a queue and then dequeue this constitutes a publish subscribe one to one. If you need multiple subscribers then you would have to somehow create an array of queues. When someone subscribes, you add a new queue to the array. The publisher in this case would have to put the message onto all the queues.

Eugen Graf · May 9, 2007

QUOTE(Michael_Aivaliotis @ May 8 2007, 04:16 AM)

Are you referring to a specific vi server method or the general concept of publish/subscribe?
I would think that if you create a queue and then dequeue this constitutes a publish subscribe one to one. If you need multiple subscribers then you would have to somehow create an array of queues. When someone subscribes, you add a new queue to the array. The publisher in this case would have to put the message onto all the queues.

Thanks Michael, I need generally informations to publish subscriber in relation to Labview, how to and examples. Are there any? Or should I make me one myself?

Queues in array should be variant? I think, yes. A little example code, which only explains how to implement a easy one?

Eugen

JDave · May 9, 2007

QUOTE(Eugen Graf @ May 8 2007, 12:43 AM)

Thanks Michael, I need generally informations to publish subscriber in relation to Labview, how to and examples. Are there any? Or should I make me one myself?
Queues in array should be variant? I think, yes. A little example code, which only explains how to implement a easy one?

Eugen

I don't know of any examples for publish-subscribe except for DataSocket -- search for 'subscribe' in the Example finder and only one comes up. There are several ways of accomplishing this, and Michael suggested a good one. Variants would make it flexible. Some different ways of doing publish-subscribe are

DataSocket, programmatic -- this is lossy, but gives you programmatic control over who is publishing and subscribing and when
DataSocket, front panel -- also lossy, can bind a control to a datasocket or shared variable without any code
Queues -- not lossy, must create separate queue for each subscriber
Functional Global -- probably lossy, no intrinsic way of notifying subscribers that new data is available
User Events -- not lossy, can notify many subscribers with one event, must individually 'register' for event in each subscriber. I like this one because once you set up the registration, you just fire one event to publish.

That surely isn't all of the available methods, but you can look for examples in any of those areas. For User Events I would look at the examples "Dynamically Monitor Vi's.vi", "Dynamically Register for Events.vi", and "Programmatically Fire Events.vi"

David

Justin Goeres · May 10, 2007

QUOTE(Eugen Graf @ May 7 2007, 11:43 PM)

Thanks Michael, I need generally informations to publish subscriber in relation to Labview, how to and examples. Are there any? Or should I make me one myself?
Queues in array should be variant? I think, yes. A little example code, which only explains how to implement a easy one?

I regularly do something like this, but the term I use for them is observers. I have a hunch that Publish/Subscribe and Observer may have very distinct meanings in software design, and I'm not completely sure my term is strictly correct -- if someone has semantic arguments to make either way I'd be all ears.

I frequently use a variant queue, although it depends on the context. If all my observers to a particular resource will be getting the same type of data, I would typically define the queue for that data (and typedef the data). But in a general sense, the variant queue works fine.

I've hacked up a little example (in LV80) that illustrates basically what I do. This example has a simple "Publish!" button and an associated DBL value that is published to any of 3 registered observers. Each observer can be registered and unregistered with buttons on the UI.

Good Luck!

Justin

http://forums.lavag.org/index.php?act=attach&type=post&id=5777

http://forums.lavag.org/index.php?act=attach&type=post&id=5775

http://forums.lavag.org/index.php?act=attach&type=post&id=5776

Eugen Graf · August 24, 2007

I thank you all. I use Pub/Sub model in one project now. It's really cool. I can see all queues traffic, all themes and tasks:

http://forums.lavag.org/index.php?act=attach&type=post&id=6729

My StartUp VI looks like in following example:

http://forums.lavag.org/index.php?act=attach&type=post&id=6730

My Dispatcher Task is here:

http://forums.lavag.org/index.php?act=attach&type=post&id=6731

And on this example you can see, how my modules (tasks) say to dispather about themes (topics) while starting:

http://forums.lavag.org/index.php?act=attach&type=post&id=6732

And this is my Create&Subscribe VI used in each task:

http://forums.lavag.org/index.php?act=attach&type=post&id=6733

A big thank to all, Eugen

ohiofudu · August 24, 2007

QUOTE(Eugen Graf @ Aug 23 2007, 09:18 AM)

I thank you all. I use Pub/Sub model in one project now. It's really cool. I can see all queues traffic, all themes and tasks:
A big thank to all, Eugen

Hi Eugen

Like to learn This one...Can you please post your complete Vi??

Thanks

Eugen Graf · August 24, 2007

QUOTE(ohiofudu @ Aug 23 2007, 04:31 PM)

Hi Eugen
Like to learn This one...Can you please post your complete Vi??

Thanks

Here are 4 VIs and 1 Typedef I used. I can't post my whole project, because of rights. But you can see on screenshots, how I use them.

Eugen

Mike Ashe · August 25, 2007

Nice example Eugen, this could be worked into something suitable for the Code Repository, as well as Wiki.

:thumbup:

Eugen Graf · August 25, 2007

QUOTE(Mike Ashe @ Aug 24 2007, 03:41 AM)

Nice example Eugen, this could be worked into something suitable for the Code Repository, as well as Wiki.
:thumbup:

Thank you, but this example is not completely made yet. If you want tu unsubscribe some tasks (modules), you have to duplicate the subscribe case in dispatcher and replace the true constant to false.

http://forums.lavag.org/index.php?act=attach&type=post&id=6756 ''>http://forums.lavag.org/index.php?act=attach&type=post&id=6756 '>http://forums.lavag.org/index.php?act=attach&type=post&id=6756

And I have two problems too:

1. I want to mix the communication with Notifiers and user events (I think here on a 3d topic table or array).

2. private topics should stay in module and must be not published to other modules, so I don't want to subscribe them on dispatcher.

Eugen

ohiofudu · August 29, 2007

QUOTE(Eugen Graf @ Aug 23 2007, 09:38 AM)

Here are 4 VIs and 1 Typedef I used. I can't post my whole project, because of rights. But you can see on screenshots, how I use them.
Eugen

Danke Eugen,

The Vis are helpfull,I will have to take sometime out to analyze them to figure out how you use them.

Danke nochmal.

Eugen Graf · October 27, 2007

Hello, anybody, who is interested can try my new version. This uses TCP/IP protocol, so you can transfer data over network.

Cheers, Eugen

Eugen Graf · October 27, 2007

Here a screenshot.

Eugen Graf · October 30, 2007

A new version of my Pub/Sub is available. Now you can connect one Dispatcher to an other and select/subscribe availabe topics of them. Furthermore is the TCP/IP transfer protocol some better, syncbytes and checksum are implemented now. And if a client is disconnected, but forgotten to unsubscribe, it will be removed automatically from the topic table.

Eugen