Storing data in a csv file error (running code in parallel)

[achodankar]

Hello Developers,
The values in the csv file are random and don’t make sense. I am using the same code for storing data in csv file. It stores the correct values when the code is not run parallelly.

The code snippet:

{
SuperLatticePhysVelocity2D<T,DESCRIPTOR> velocityF(sLattice, converter);
BlockReduction2D2D<T> velocityPlane(velocityF,12, BlockDataSyncMode::ReduceOnly);
ofstream myfile1;
myfile1.open(“velocity_”+ std::to_string(iT) + “.csv”);
myfile1 << “i,” << “j,” << “Ux,” <<“Uy”<< std::endl;
int latticeR[2] { };
for (latticeR[0]=0; latticeR[0] < velocityPlane.getBlockStructure().getNx(); ++latticeR[0])
{
for (latticeR[1]=0; latticeR[1] < velocityPlane.getBlockStructure().getNy(); ++latticeR[1])
{
T vel[2] { };
velocityPlane(vel, latticeR);
myfile1 << latticeR[0] << “,” << latticeR[1] << “,”<< vel[0] << “,”<< vel[1] << std::endl;
}
}
myfile1.close();

}

I would really appreciate feedback on this matter.

Thank you.

Yours sincerely,

Abhijeet

[Adrian]

You have to ensure that the IO only happens in the main process (where BlockDataSyncMode::ReduceOnly syncs to). Otherwise each process will write to the same file in parallel and in addition not even have the correct data.

[achodankar]

Hello Adrian,
What do you mean by “IO only happens in the main process”? The code snippet is included in the getResults function and called in the main program. I would really appreciate help in this matter.

Thank you.

Yours sincerely,

Abhijeet

[Adrian]

The snippet performs filesystem write operations using std::ofstream. As far as I can tell without seeing the full code, this is not restricted to the rank 0 process (where the reduced data is communicated to by BlockReduction2D2D). Thus all processes execute this the std::ofstream code and write to the same file. When using e.g. OpenLB’s default VTK writer this is resolved transparently in the background.

[achodankar]

Hello Adrian,
Thank you for your feedback. I will try to work it out and meanwhile use the default VTK results temporarily.

Thank you.

Yours sincerely,

Abhijeet

[syed]

Did you solve the problem? I am stuck with the same problem.

[Author]

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