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| Reporter | millszg | Assigned To | henry | |
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| Priority | normal | Severity | minor | Reproducibility | always |
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| Status | resolved | Resolution | fixed | |
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| Platform | x86-64 | OS | Ubuntu | OS Version | 18.04 |
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| Product Version | 8 | |
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| Fixed in Version | | |
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| Summary | 0003537: faceAgglomerate hangs for certain values of nFacesInCoarsestLevel and featureAngle in parallel |
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| Description | faceAgglomerate will occasionally hang for certain values of nFacesInCoarsestLevel and featureAngle. This only occurs when running in parallel, and the same values that cause it to hang for a certain number of processors will work for a different number of processors. Increasing nFacesInCoarsestLevel will sometimes alleviate it, but oftentimes it needs to be increased so much that very little agglomeration is actually occurring. In runs where the program hangs, it will always print "Agglomerating patch : patch_name" at least one time, but will not always print for each patch being agglomerated. Keeping everything the same, but rearranging the order of patches in the viewfactorsDict file will usually lead to the programming hanging after outputting "Agglomerating patch..." for a different patch. From what I have tested, this occurs in OpenFOAM 6, 7, 8 and dev. I have had this issues with multiple different meshes and on different computers. From what I have found, this is actually caused by a bug in the pairPatchAgglomeration class (see additional information for explanation).
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| Steps To Reproduce | A case which will reproduce the error is attached. It is a single region of a multiregion case, so some of the boundaries are mappedWall. This error was occurring with the entire multi-region mesh was included in the case folder, so the use of mapped walls without the patch being mapped to is not the cause of the issue. The mesh has already been generated and calling faceAgglomerate will cause it to hang. The culprit seems to be innerGas_to_holderBase. When nFacesInCoarsestLevel for the patch is set to 7000, faceAgglomerate hangs. When it is increased to 10000, it will complete successfully. When the innerGas_to_holderBase is the first in the list of patch dictionaries in viewFactorsDict, faceAgglomerate seems to hang on innerGas_to_retort. When it's the fourth dictionary (between innerGas_to_tempDisks and innerGas_to_retort), faceAgglomerate seems to hang on innerGas_to_retortInlet. |
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| Additional Information | From debugging it appears the problem is in the pairPatchAgglomeration class. In the agglomerate() function, at least one process hangs while the rest continue, causing the program to be unable to continue. This seems to happen in the do-while loop where the agglomOK variable for processes that hang remains false, while it is set to true for the other processes and they complete the function. The issue seems to be resolved by adding in a call to reduce the agglomOK variable with an orOp operation the reduce operation for nCoarseFaces on line 412 of pairPatchAgglomeration.C (in version 8). I have attached a copy of pairPatchAgglomeration.C that I am using, which is no longer causing the error for me. |
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| Tags | No tags attached. |
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