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POHow to have different OpenMP threads execute different tasks
 

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  1. POHow to have different OpenMP threads execute different tasks
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    <p>I am using open MP to speed up the flux calculation in my program. I basically want OpenMP to carry out both of these left and right flux calculations in parallel. But on the contrary, the following code takes even more time with the <code>#pragma</code> directives. What do i modify to get it right?</p> <pre><code>#pragma omp parallel num_threads(2) { #pragma omp single {//first condition //cerr&lt;&lt;"Executed thread 0"&lt;&lt;endl; if ( (fabs(lcellMach-1.0)&lt;EPSILON) || ( (lcellMach-1.0) &gt; 0.0 ) ){//purpose of Epsilon!!!! FluxP[0] = rhol * vnl; FluxP[1] = rhol * ul * vnl + Pl*nx; FluxP[2] = rhol * vl * vnl + Pl*ny; FluxP[3] = rhol * wl * vnl + Pl*nz; FluxP[4] = rhol * ((GAMMA * Pl / (rhol * (GAMMA-1.0))) + ((ul*ul + vl*vl + wl*wl)/2.0)) * vnl; }else if ( (fabs(lcellMach+1.0)&lt;EPSILON) || ( (lcellMach+1.0) &lt; 0.0 ) ){ FluxP[0] = FluxP[1] = FluxP[2] = FluxP[3] = FluxP[4] = 0.0;// If flow direction is opposite the Flux + is zero }else { double ql = (ul*ul + vl*vl + wl*wl);// how did this come FluxP[0] = rhol * lcell_a * (lcellMach+1.0)*(lcellMach+1.0) / 4.0; FluxP[1] = FluxP[0] * ( ul + (nx*(0.0-vnl + 2.0*lcell_a)/GAMMA) ); FluxP[2] = FluxP[0] * ( vl + (ny*(0.0-vnl + 2.0*lcell_a)/GAMMA) ); FluxP[3] = FluxP[0] * ( wl + (nz*(0.0-vnl + 2.0*lcell_a)/GAMMA) ); FluxP[4] = FluxP[0] * ( ((ql - vnl*vnl)/2.0) + (((GAMMA-1.0)*vnl + 2.0*lcell_a)*((GAMMA-1.0)*vnl + 2.0*lcell_a) / (2.0*(GAMMA*GAMMA-1.0))) ); } }//end of 1st #pragma omp single {//second condition //cerr&lt;&lt;"Executed thread 1"&lt;&lt;endl; if ((fabs(rcellMach+1.0)&lt;EPSILON) || ((rcellMach+1.0) &lt; 0.0)) { FluxM[0] = rhor * vnr; FluxM[1] = rhor * ur * vnr + Pr*nx; FluxM[2] = rhor * vr * vnr + Pr*ny; FluxM[3] = rhor * wr * vnr + Pr*nz; FluxM[4] = rhor * ((GAMMA * Pr / (rhor * (GAMMA-1.0))) + ((ur*ur + vr*vr + wr*wr)/2.0)) * vnr; }else if ((fabs(rcellMach-1.0)&lt;EPSILON) || ((rcellMach-1.0) &gt; 0.0)) { FluxM[0] = FluxM[1] = FluxM[2] = FluxM[3] = FluxM[4] = 0.0; }else { tempFlux[0] = rhor * vnr; tempFlux[1] = rhor * ur * vnr + Pr*nx; tempFlux[2] = rhor * vr * vnr + Pr*ny; tempFlux[3] = rhor * wr * vnr + Pr*nz; tempFlux[4] = rhor * ((GAMMA * Pr / (rhor * (GAMMA-1.0))) + ((ur*ur + vr*vr + wr*wr)/2.0)) * vnr; double qr = (ur*ur + vr*vr + wr*wr); tempFluxP[0] = rhor * rcell_a * (rcellMach+1.0)*(rcellMach+1.0) / 4.0; tempFluxP[1] = tempFluxP[0] * ( ur + (nx*(0.0-vnr + 2.0*rcell_a)/GAMMA) ); tempFluxP[2] = tempFluxP[0] * ( vr + (ny*(0.0-vnr + 2.0*rcell_a)/GAMMA) ); tempFluxP[3] = tempFluxP[0] * ( wr + (nz*(0.0-vnr + 2.0*rcell_a)/GAMMA) ); tempFluxP[4] = tempFluxP[0] * ( ((qr - vnr*vnr)/2.0) + (((GAMMA-1.0)*vnr + 2.0*rcell_a)*((GAMMA-1.0)*vnr + 2.0*rcell_a) / (2.0*(GAMMA*GAMMA-1.0))) ); for (int j=0; j&lt;O; j++) FluxM[j] = tempFlux[j] - tempFluxP[j]; } } }//pragma </code></pre> <p>Urgent help required. Thanks.</p>
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    1. PTQuestion
    1. USJonathan Dursi
    1. USAakash Anuj
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    1. CO#pragma omp single: The omp single directive identifies a section of code that must be run by a **single available thread**.
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      1. POHow to have different OpenMP threads execute different tasks
      1. USnhahtdh
    2. COThen what do i do here? I need to execute both of the blocks of code inside the single sections in parallel.
      singulars
      1. POHow to have different OpenMP threads execute different tasks
      1. USAakash Anuj
    3. COThis can be done; @nhahtdh's comment describes the problem, and Hristo's answer correctly describes how to do what you were trying to do. But this seems like an overly low-level place to be doing the parallelization. Presumably at some higher level of the code you're doing this flux calculation over many cells, correct? That loop seems like a more profitable target for parallelization.
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      1. POHow to have different OpenMP threads execute different tasks
      1. USJonathan Dursi
 

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