Starting state machine within running state machine

[jasonpfi]

Is there a way to call another XML file from the state machine that is currently executing?

I want to start another State Machine based on a state of the current machine. So far I have used "" with both the absolute directory path and the URL of the XML file hosted on an apache server. Neither has worked.

I had an idea to add a listener to the current state machine and spawn another interpreter if a certain state was achieved, but this seems to have barriers to the approach.

Any help would be appreciated!

[jasonpfi]

Note: I am using SCXML.

[jasonpfi]

Example: I always get a timeout

\ \ \ \ \ \ \ \ \ \ \ \ \

[jbeard4]

You are doing this correctly, but SCION does not currently support <invoke>. The next version of SCION will support <invoke>, so please stand by. Thanks.

[jasonpfi]

Great! Any idea on when this is going to be released?

[jbeard4]

Maybe next week

[jasonpfi]

Hi, Any idea when the invoke tag will be implemented in the code base?

[jbeard4]

Pretty soon. I am getting it ready for release.

[jbeard4]

@jasonpfi Hi. The the latest version of scion released today (4.3.1) supports <invoke>. I would appreciate if you could please give it a try, and report any bugs. Thanks.

[jasonpfi]

Great, will definitely give it a try on Monday.

[Getafix-hub]

Thanks Jacob! I will test invoke later this week

[jbeard4]

Great, I look forward to your feedback. Thanks

[Getafix-hub]

The invoke is basically working, but is there a way to make the parent context accessible? for example, in the parent script, I can send a websocket message: ws.send(s) but that does not work in the child script

Parent scxml extract

    <state id="state2">
        <onentry>
            <script>
                <log label="In state2"/>
            </script>
        </onentry>

        <invoke src="echoChild.xml" type="scxml">
            <finalize/>
        </invoke>

        <transition event="done.invoke.state2.*" target="fstate">
            <log label="Received event done.invoke.state2.*"/>
        </transition>

        <transition event="error.invoke.state2.*" target="fstate">
            <log label="Received event error.invoke.state2.*"/>
        </transition>
    </state>

echoChild.xml: (update: moved transition outside onentry block)

<?xml version="1.0" encoding="UTF-8"?>
<scxml xmlns="http://www.w3.org/2005/07/scxml" version="1.0" initial="idle">

    <datamodel>
        <data id="msg" expr="[7,8,9]"/>
    </datamodel>

    <state id="idle">
        <onentry>
            <log label="Echo Child - idle state"/>
            <script>
                const json = {
                    "type": "MSG_ECHO", 
                    "value": { "msg": msg  }};
                const s = JSON.stringify(json);
                console.log('In idle ' + s);
                ws.send(s);
            </script>
        </onentry>

         <transition event="MSG_ECHO" target="fstate">
                <log label="Received MSG_ECHO"/>
         </transition>
    </state>

    <final id="fstate">
        <onentry>
            <log label="Echo Child - final state"/>
        </onentry>
    </final>

</scxml>

[jbeard4]

SCXML supports data sharing between parent and child invoked instances through the use of the param element. This lets you initialize data in the child session to data from the parent session. You can find an example of this in test226 of the scxml IRP test suite.

https://github.com/jbeard4/scxml-test-framework/blob/master/test/w3c-ecma/test226.txml.scxml

https://github.com/jbeard4/scxml-test-framework/blob/master/test/w3c-ecma/test226sub1.scxml

[Getafix-hub]

Thanks!

I was able to share the ws websocket from the parent

`

        <finalize/>
    </invoke>

to the child state machine

`

would you have any pointer showing how the child state machine can receive the events:

• Can the parent state machine forward events to a child state machine?
• Can a child state machine register for event notifications to receive all the parent's events?

[jbeard4]

In general, I recommend reviewing the spec for <invoke> and <send>: https://www.w3.org/TR/scxml/#invoke https://www.w3.org/TR/scxml/#send

Can the parent state machine forward events to a child state machine?

There are two ways to achieve this:

• If you want to automatically forward all events received by the parent to the child, then use invoke/@autoforward.
• If you only want to send specific events to received by the parent to the child (i.e., filter the events that are sent), then you can use the <send> action inside of a targetless transition with @target=#_invokeid.

Can a child state machine register for event notifications to receive all the parent's events?

Just use regular transitions in the child state machine to handle the events sent by the parent.

If this support is helpful, please consider backing the project on OpenCollective. It really helps to sustain the project. Thank you!

[Getafix-hub]

Thank you! As far as I can tell, Invoke feature works as expected

[jbeard4]

Thank you for trying it out and providing feedback.