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Eventqueue runs full [message #1839110]

Sun, 14 March 2021 15:05

Christoph Schultz

Messages: 5
Registered: February 2021

Junior Member

Hello,
I have build the following set up:
- 1 Forte Instance that reads messages from a mqtt broker runnning on a raspberry pie and decodes the messages to certain commands
these are send via publish and subsribe blocks to another forte
- 1 Forte Instance that will execute commands running on an EV3

I sometimes get the Error that the eventqueue runs full.
Which leads to the system (EV3) beeing not responsive anymore and executing the last command eternally.

I only used QW and QX + some convert Blocks on the EV3 to minimize the load on this part.

In another topic i read something like you can increase the size of the queue.
How would i do that? Could that even help.
I already reduced the incomming events by
a) synchronizing/merging events
b) building little "pause" statements in the Python Skript that i use to send the mqtt messages.

How do i find out, which block has a full event queue?
How do i increase the number of events allowed in the queue
Is there a mechanism, that can help preventing system failure, when the queue runs full. E.g flush the queue?

Even some kind of emergency stop could not reach the EV3 since that would be event trigged also, and new events are ignored.

Also i would like to build in some measurements for the timing.
I found that you implemented some kind of TIME() function.

Are there ways to synchronize the time between all the device that participate in this distributed system?
E.g. with NTP?
Or is that something that i would have to implement myself as a service fb?

Best Regards

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Re: Eventqueue runs full [message #1839116 is a reply to message #1839110]

Sun, 14 March 2021 19:59

Alois Zoitl

Messages: 1585
Registered: January 2014

Senior Member

Hi,

sofar in most of the cases when an event queue gets full increasing the event queue delays the problem only a bit and does not cure the root cause. In the default setup you have one internal and one external event queue per resource. You can increase both sizes in the advanced section of the CMake setup.

How many messages are you sending. What is the time between them? Is it possible to have a look on the app part running on EV3? You can also send it to my email if you don't want to publish it publicly.

Since 4diac FORTE 1.13.0 we have two functions one is NOW() and one is NOW_MONOTONIC. The first gives you the current time as DATE_AND_TIME based on the OS time. If you have timesynch in your OS you will also have synced times in 4diac FORTE. I think Martin who made both also implemented them as FBs.

I hope this helps,
Alois

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