[zhangyan]

Hi everyone,

I met a question about message sending and receiving.

What I want to do is:
each slave sends a fvPatchScalarField to master, and do some manipulation in master, then send other fvPatchScalarField back to each slave.

Here is my first attempt:

forAll(input_.boundaryField(), patchi)
{
    const fvPatchScalarField& inputFaces = input_.boundaryField()[patchi];
    fvPatchScalarField& resultFaces = result_.boundaryFieldRef()[patchi];

    if (Pstream::master())
    {
        List<autoPtr<IPstream>> IPL(nProc - 1);
        List<autoPtr<OPstream>> OPL(nProc - 1);
        for(label iProc = 1; iProc < nProc; iProc++)
        {
            IPL[iProc - 1].set(new IPstream(Pstream::commsTypes::blocking, iProc));
            OPL[iProc - 1].set(new OPstream(Pstream::commsTypes::blocking, iProc));
        }

        //update master
        forAll(inputFaces, facei)
        {
            getResult
            (
                inputFaces[facei],
                resultFaces[facei]
            );
        }
            
        // update each slave
        for(label iProc = 1; iProc < nProc; iProc++)
        {
            scalarField inputFacesTemp;
            IPL[iProc - 1]()() >> inputFacesTemp;
            scalarField resultFacesTemp(inputFacesTemp.size());
            forAll(inputFacesTemp, facei)
            {
                getResult
                (
                    inputFacesTemp[facei],
                    resultFacesTemp[facei]
                );
            }
            OPL[iProc - 1]()() << resultFacesTemp;
        }
    }
    else
    {
        OPstream(blocking,Pstream::masterNo())() 
            << dynamic_cast<scalarField&>(inputFaces);
        IPstream(blocking,Pstream::masterNo())()
            >> dynamic_cast<scalarField&>(resultFaces);
    }
}

However, after decomposition, the patch numbers in each processor maybe not equal. This will cause error because of the first line of my code, where the loop times are equal to the patch numbers of each processor.
Let us suppose patch numbers in master is 4, and patch numbers in slave1 is 5.
Then in master, the loop times is 4. It should receive 4 scalarFields and send 4 scalarFields in master.
But in slave1, it will send 5 scalarFields and receive 5 scalarFields.
Send and receive do not match!


Here is my second try (simplified, scalar on behalf of scalarField):

#include "fvCFD.H"

int main(int argc, char *argv[])
{
    #include "setRootCaseLists.H"

    label nProc = Pstream::nProcs();
    if (Pstream::master())
    {
        List<List<autoPtr<IPstream>>> IPL(nProc - 1);
        List<List<autoPtr<OPstream>>> OPL(nProc - 1);

        for(label iProc = 1; iProc < nProc; iProc++)
        {
            IPL[iProc - 1].resize(5);
            OPL[iProc - 1].resize(5);
            
            for(label i = 1; i < IPL[iProc - 1].size(); i++)
            {
                IPL[iProc - 1][i].set(new IPstream(Pstream::commsTypes::blocking, iProc));
                OPL[iProc - 1][i].set(new OPstream(Pstream::commsTypes::nonBlocking, iProc));
                scalar b;
                IPL[iProc - 1][i]()() >> b;
                Info << "b===" << b <<endl;
                OPL[iProc - 1][i]()() << b;
                Info << "send b over !!!"  <<endl;
            }
        }
    }
    else
    {
        for(label i = 1; i < 5; i++)
        {
            Pout << "I am in proc ID: ===" << Pstream::myProcNo()
                 << "i ===" << i <<endl;
            scalar a = Pstream::myProcNo();
            OPstream(Pstream::commsTypes::blocking, Pstream::masterNo())() << a;
            scalar c;
            IPstream(Pstream::commsTypes::blocking, Pstream::masterNo())() >> c;
            Pout << "c===" << c <<endl;
        }
    }

    Info<< "End\n" << endl;

    return 0;
}

But the above code doesn't work well. It gets stuck after the first time of "send b over".

Could anyone help me?