communication callbacks in libsim

[markcmiller86]

Date: Fri, 23 Aug 2019 05:13:56 -0700
From: mdorier at anl.gov (Dorier, Matthieu)
This post was imported from the visit-users@ornl.gov email archive

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Hi,

This is more of  a curiosity question: in LibSim, we have to setup communication callbacks using
VisItSetBroadcastIntFunction2 and VisItSetBroadcastStringFunction2. In literally all the simulations
I?ve seen, these functions simply call MPI_Bcast. Given that VisIt itself relies on MPI (with even
the possibility to set the MPI communicator using VisItSetMPICommunicator), why are these callbacks
necessary? Why isn?t VisIt directly using MPI_Bcast?

Thanks,

Matthieu

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[markcmiller86]

Date: Fri, 23 Aug 2019 09:36:47 -0700
From: bjw at ilight.com (Brad Whitlock)
This post was imported from the visit-users@ornl.gov email archive

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I didn?t design that part but my take is that by doing communication via callbacks, the simV2 front
end library can be used for either serial or parallel by keeping MPI out of it. Otherwise, we?d
probably need a simV2_ser and simV2_par library.

Brad

> On Aug 23, 2019, at 5:13 AM, Dorier, Matthieu via visit-users <visit-users at elist.ornl.gov>
wrote:
>
> Hi,
>
> This is more of  a curiosity question: in LibSim, we have to setup communication callbacks using
VisItSetBroadcastIntFunction2 and VisItSetBroadcastStringFunction2. In literally all the simulations
I?ve seen, these functions simply call MPI_Bcast. Given that VisIt itself relies on MPI (with even
the possibility to set the MPI communicator using VisItSetMPICommunicator), why are these callbacks
necessary? Why isn?t VisIt directly using MPI_Bcast?
>
> Thanks,
>
> Matthieu
> --

> Frequently Asked Questions for VisIt: https://wci.llnl.gov/simulation/computer-
codes/visit/FAQ.html <https://wci.llnl.gov/simulation/computer-codes/visit/FAQ.html>

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