Re: Suspending and Resuming a hard real time task

On 12/16/2015 03:35 PM, Jonas Schulze wrote:
>
> Hi,
>
> in my project I am using a soft real time task to perform some 
> computations and network communications, and a periodic hard real time 
> task in a different thread to perform other computations.
>
> For the network communications in soft real time I need to use an 
> third party API. Now the program crashed at random places with 
> “malloc() corruption (fast)” error. Our conclusion was that the 
> program crashes if the soft real time task is paused due to the 
> activation of the hard real time task, while it is carring out the 
> “read” or “write” network functions. So what we did is
>
> .
>
> .
>
> .
>
> Rt_task_suspend(hrt_task)
>
> Network read/write
>
> Rt_task_resume(hrt_task)
>
> .
>
> .
>
> .
>
> To ensure the hard real time task is never activated while the network 
> functions are at work. After using the suspend and resume the program 
> does not crash anymore.
>

What above conflicts with the idea of real time. In fact if you can 
suspend a hard real time task to let a soft real time run, you are 
forcing a priority inversion, i.e allowing hard real time to be blocked 
by a not hardened task.
If it works the you do not need hard real time and stay happy with plain 
Linux.

> My questions are
>
> 1.is this is the right way to prevent a periodic real time task from 
> interrupting another function?
>
One of the many possible,  but is a bit nonsensical.
>
> 2.After suspending and resuming, is the task still in hard real time 
> or do I need to make another call to make_hard_realtime()?
>
The hard real time state is not touched by a task suspend, whoever emits it.

> 3.Should I use rt_task_make_periodic() instead of rt_task_resume()?
>
No.

Paolo
>
> Thanks and Best Regards
>
> Jonas
>
> *---------------------------*
>
> *Jonas Schulze, M. Sc.*
>
> Technische Universität Darmstadt
>
> Flugsysteme und Regelungstechnik
>
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>
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>
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What above conflicts with the idea of real time. In fact if you can 
suspend a hard real time task to let a soft real time run, you are 
forcing a priority inversion, i.e allowing hard real time to be blocked 
by a not hardened task.
If it works the you do not need hard real time and stay happy with plain 
Linux.

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