# PetscCommGetComm
get a new MPI communicator from a PETSc communicator that can be passed off to another package 
## Synopsis
```
#include "petscsys.h"   
PetscErrorCode PetscCommGetComm(MPI_Comm comm_in, MPI_Comm *comm_out)
```
Collective


## Input Parameter

- ***comm_in -*** Input communicator



## Output Parameters

- ***comm_out -*** Output communicator



## Notes
Use `PetscCommRestoreComm()` to return the communicator when the external package no longer needs it

Certain MPI implementations have `MPI_Comm_free()` that do not work, thus one can run out of available MPI communicators causing
mysterious crashes in the code after running a long time. This routine allows reusing previously obtained MPI communicators that
are no longer needed.




## See Also
 `PetscObjectGetNewTag()`, `PetscCommGetNewTag()`, `PetscCommDestroy()`, `PetscCommRestoreComm()`

## Level
developer

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/sys/objects/tagm.c.html#PetscCommGetComm">src/sys/objects/tagm.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/sys/objects/tagm.c)


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