# New Multithreaded LagrangianParticleTracker.
**URL:** https://discourse.paraview.org/t/new-multithreaded-lagrangianparticletracker/1838
**Category:** Tips and Tricks
**Created:** [May 13, 2019, 12:01pm UTC](https://discourse.paraview.org/t/new-multithreaded-lagrangianparticletracker/1838 "2019-05-13T12:01:36Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [May 13, 2019, 12:01pm UTC](https://discourse.paraview.org/t/new-multithreaded-lagrangianparticletracker/1838/1 "2019-05-13T12:01:36Z")
**Multithreaded LagrangianParticleTracker**
The LagragianParticleTracker filter, provided in a Plugin in ParaView,
has been reimplemented with an multithreaded algorithm using VTK SMP backed that one can benefit from when using TBB or OpenMP as SMP backend when compiling ParaView.
Note that those changes imply some update on user-developed Lagrangian Integration models
as some method signatures have been modified.
**Important code changes**
1. A few methods signatures of vtkLagrangianParticleTracker, vtkLagrangianBasicIntegrationModel and vtkLagrangianParticle have changed:
- vtkLagrangianParticleTracker::Integrate/ComputeNextStep(vtkInitialValueProblemSolver\* integrator, …): Integrator are now passed to this method for further usage;
- vtkLagrangianBasicIntegrationModel::FonctionValues/FindInLocator(vtkLagrangianParticle\* particle, … ): There is no concept of CurrentParticle anymore and the particle are passed through these methods;
- vtkLagrangianParticle::SetLastCell(vtkAbstractCellLocator\* locator, …): The particle is now fully responsible of tracking last locator, data, cell and weights;
1. Accessing flow or surface data within your FonctionValues is also now a little bit different:
```auto
// Fetch flowVelocity at index 3
double flowVelocity[3];
if (this->GetFlowOrSurfaceDataNumberOfComponents(3, dataSet) != 3 ||
!this->GetFlowOrSurfaceData(3, dataSet, cellId, weights, flowVelocity))
{
vtkErrorMacro(<< "Flow velocity is not set in source flow dataset or "
"have incorrect number of components, cannot use Matida”
“equations");
return 0;
}
```
1. Some methods now need to be thread-safe, so that may impact your own implementation. Here is the exhaustive list:
```auto
In vtkLagrangianParticleTracker:
GetNewParticleId
Integrate
ComputeNextStep
In vtkLagrangianBasicIntegrationModel:
FonctionValues
FindInLocators
CheckFreeFlightTermination
ManualIntegration
FindInLocator
TerminateParticle
BounceParticle
BreakParticle (use ParticleQueueMutex before adding new particle)
InteractWithSurface (use ParticleQueueMutex before adding new particle)
IntersectWithLine
InterpolateNextParticleVariables
CheckSurfacePerforation
GetSeedArray
GetFlowOrSurfaceData
GetFlowOrSurfaceDataNumberOfComponents
GetFlowOrSurfaceDataFieldAssociation
```
1. A few mutexes are present in the code, the only one you may need to use would be vtkLagrangianBasicIntegrationModel::ParticleQueueMutex before adding particles in the particleQueue, e.g. when interacting with a surface.
---
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [December 20, 2019, 5:09pm UTC](https://discourse.paraview.org/t/new-multithreaded-lagrangianparticletracker/1838/2 "2019-12-20T17:09:38Z")
Almost all mutexes have been removed providing an even better speedup. See here :
[https://gitlab.kitware.com/vtk/vtk/merge\_requests/6240](https://gitlab.kitware.com/vtk/vtk/merge_requests/6240)
---
### Author:  [@sharon](https://discourse.paraview.org/u/sharon)
#### Post date: [January 12, 2020, 1:38pm UTC](https://discourse.paraview.org/t/new-multithreaded-lagrangianparticletracker/1838/3 "2020-01-12T13:38:25Z")
Hi Mathieu,
To make TBB enable, should i use “VTK\_SMP\_IMPLEMENTATION=TBB” or “VTK\_SMP\_IMPLEMENTATION\_TYPE=TBB”?
I can found “VTK\_SMP\_IMPLEMENTATION\_TYPE” in one of cmake files but cannot find VTK\_SMP\_IMPLEMENTATION" which is suggested in paraview build [https://github.com/Kitware/ParaView/blob/master/Documentation/dev/build.md](https://github.com/Kitware/ParaView/blob/master/Documentation/dev/build.md)
---
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [January 12, 2020, 7:19pm UTC](https://discourse.paraview.org/t/new-multithreaded-lagrangianparticletracker/1838/4 "2020-01-12T19:19:32Z")
VTK\_SMP\_IMPLEMENTATION\_TYPE=TBB
There is a typo in build.md.
---
### Author:  [@sharon](https://discourse.paraview.org/u/sharon)
#### Post date: [January 13, 2020, 12:09pm UTC](https://discourse.paraview.org/t/new-multithreaded-lagrangianparticletracker/1838/5 "2020-01-13T12:09:38Z")
Thank you Mathieu for your answers!
Best Regards,
Sharon
---
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [January 17, 2020, 9:56am UTC](https://discourse.paraview.org/t/new-multithreaded-lagrangianparticletracker/1838/6 "2020-01-17T09:56:46Z")
@sharon : Do you think you could take care of correcting the typographic issue ? That would be nice of you.
---
### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [February 13, 2020, 7:44am UTC](https://discourse.paraview.org/t/new-multithreaded-lagrangianparticletracker/1838/7 "2020-02-13T07:44:39Z")
[https://gitlab.kitware.com/paraview/paraview/merge\_requests/3918](https://gitlab.kitware.com/paraview/paraview/merge_requests/3918)