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drjdpowell

[LVTN] Messenger Library

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Your right, there is a reference leak here.  That Queue is a reference created in the actor's calling code, and is used to trigger the "Autoshutdown" message when the caller stops, thus invalidating the Queue.  There is an async component called the "ReferenceMonitor" which watches that Queue and sends the Autoshutdown message then closes.   ReferenceMonitor also polls the actor's address, so it can shut itself down if the actor dies.  However, I forgot to destroy the Queue in that case.   Here is an image where I have added the needed Close operation:

2146204797_FixReferenceLeak.png.3fb51efbe10eae86af6c78643cb176a8.png

 

Thank for spotting this,

-- James

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Hi Dr James,

Recently I've been thinking about the security when of TCP messengers. For example,
often I am communicating with actors from TestStand steps. Everything runs on the same PC,
works perfectly. However, I realised that if potential attacker knows the port of the actor,
he/she will be able to connect to my actors from outside and potentially do harm.

At the moment I see 2 solutions:

1. To configure Windows Firewall for the main application to only accept local connections.

2. To bind TCP socket to localhost by specifying "net address" here:

1474620694_netaddress.png.da8c77a00114195d927d82002e6eaf9c.png

The second solution will work regardless of firewall settings.
It would be great to hear your thoughts.Thank you!

Kind Regards,
Max

 

 

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What number do I feed to "net address" to make it local host only?  I wasn't aware of such a feature.

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26 minutes ago, drjdpowell said:

What number do I feed to "net address" to make it local host only?  I wasn't aware of such a feature.

I would imagine the string 127.0.0.1 (or u32 Net Address 2130706433)

image.png.6464f93267112eda4e7c4c15170c010b.png

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Thank you for your input on this! Indeed bbean is right, it could be 127.0.0.1 or "localhost" converted to u32 net address.
As a potential idea the "net address" could be a parameter when configuring the TCP Messenger.

Thank you both!

Kind Regards,
Maksim

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Here is a beta version, 1.11.0, with changes to TCP Messengers to support the various TCP options about ports and the like.  Also adds a Keep-alive to detect half-open connections.  Bitbucket Issues 26, 27, 33.  I have not had time to do more than a basic test; it would be a help if someone could give it a try.   Note that I've replaced some of the creation VIs for TCP Messengers in the pallette (originals should still work, but I wanted to change VI names).

drjdpowell_lib_messenging-1_11.0_116.vip

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Thank you for your work Dr Powell.

I did some testing of the following VIs from the palette:

1.PNG.dce311abb6ec3c0f928d99f9aea43b07.PNG

And I can confirm that I was able to establish connection using Service Name or Specific Port and
also it was possible to isolate actor from external network by setting net address to "2130706433" (127.0.0.1).

3.PNG.036d38be53c16f6b2938fafb97f533ab.PNG

However I noticed that the "Name the TCP Service.vi" is now missing from the palette.
I could still get it from the new "Create the TCP Server.vi" and wire it as a "event messenger subtype" to "Actor Startup" VI.

Kind Regards,
Max

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Dr Powell,

Thank you for the new release of the library. It is a beautiful piece of work.

Today I faced a new challenge (sorry for bombarding the forum). One of my actors is using TestStand API to execute test sequences. I noticed strange behavior, when this
actor is executing synchronous TestStand API calls that take a noticeable time (>200ms) other actors (5 of them, fully decoupled) are also being freezed until that API call is finished.
I started researching what could cause this. I believe it is a deadlock because preferred execution system of all actors is the same:
https://zone.ni.com/reference/en-XX/help/370052W-01/tsapiref/infotopics/lv_preferred_exec/

Ideally I would like to set specific "Preferred Execution System" for actors that require it. I tried to change this setting in VI properties
for ActorNR.vi. But doing this affects whole class hierarchy and propagates to all actors (as a result they stay under the same execution system).

Idea that I have in my mind is to create another actor type that is configured for specific execution system.
It would be great to hear how would you approach this issue?

Thank you!

Kind Regards,
Maksims

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37 minutes ago, Maksim Kuznetsov said:

One of my actors is using TestStand API to execute test sequences. I noticed strange behavior, when this
actor is executing synchronous TestStand API calls that take a noticeable time (>200ms) other actors (5 of them, fully decoupled) are also being freezed until that API call is finished...

By default, subVI are set to "Same as Caller" execution system, but they can be a specific system instead.  I suspect it might be just the subVI that does the TestStand call that needs to be in a different Execution System, not the calling Actor.vi itself.  So try just changing the subVI.

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6 minutes ago, drjdpowell said:

By default, subVI are set to "Same as Caller" execution system, but they can be a specific system instead.  I suspect it might be just the subVI that does the TestStand call that needs to be in a different Execution System, not the calling Actor.vi itself.  So try just changing the subVI.

If that doesn't work you may have to separate the TestStandAPI calls out.  Are you using your TestStand Actor as a GUI or user interface?  If so you may have to create another Actor to separate out the TestStand API calls that are causing the log jam into a new Actor....That new actor should not have any property/invoke nodes which would force its VI into the UI thread.

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Thank you both for quick replies. Indeed the TestStand actor also is used as a GUI. So, it makes it difficult to call everything in SubVIs. There are cases when TestStand engine creates popups that automatically appear on top of the actor front panel (hence blocking it).

 

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Note: there is nothing stopping you putting all your code in an actor in one single subvi (which Actor.vi or ActorNR.vi then calls). So you can try this easily.

Edited by drjdpowell
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Thank you for all the suggestions! Since I based my actor on NI example of TestStand UI the SubVIs were already configured to run in a separate execution
and I still experienced blockings. That is why I thought maybe the actor itself has to run in a different execution and posted in this thread.
However today I found out that the freeze was caused by a dialog box that was created asynchronously by the TestStand API (e.g. when it noticed that sequence file was changed).
There is a "TestStand - Set TestStand Application Window.vi" that accepts VI reference and makes all the dialog boxes modal to that VI (I set it to TestStand ActorNR.vi reference).

It works perfectly fine when TestStand Actor's front panel is the front-most window, no blockings. However if another actor's front panel is currently in focus (front-most) there will be
no dialog box until I switch the focus back to TestStand Actor front panel. And in this case both actors get frozen until I acknowledge that dialog box.

P.S. Simple front panel drag around with a mouse pointer make actors unfreeze.

I think it is related to modality settings that I will explore in more details.
Thanks again James and bbean. I highly appreciate your time and support.

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You should post a topic on LAVA sometime explaining how you use Teststand and Messenger Library.  I have not had the pleasure (or is it torment?) of seriously using Teststand.

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Say I've created a number of clones of a reentrant  actor and each has a unique setup that needs to be preserved. What's the niftiest way of identifying one clone from another when saving state using JSON?

Cheers, Bob

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How does your calling code keep track of the different clones?  Match that.  If the caller gives them specific names, such as storing the actor addresses in a cluster, then use those names in a JSON object.  If, instead, the actor addresses naturally are treated as an array, then store a JSON array.

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I've got it - storing each clone by name suits a fixed architecture, storing a JSON array suits the case where the number of clones is determined at run time. 

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Exactly.  You can even do the case where the types of actor is determined at run time, in which case the caller makes a JSON object like this:

{"Actor Class Name":"MyActorX.lvclass","Config":{...}} 

Then on application load, the caller launches an actor of that class, then sends it the "Config".

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