Fix update of the magnetic field#15632
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shahor02
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@romainschotter thanks, the fix is correct.
Could you hint at how you re-initialise it in the analysis for different runs?
In principle, if it is done via GRPGeomHelper, there no need to delete the field: the field GRP is a function if timestamp rather than the run number, one simply updates the current values.
sawenzel
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July 25, 2026 09:32
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Looks ok to me.
For full consistency, one should probably also do Instance()->mFieldFast = nullptr next to the mField reset in both overloads to remove the implicit dependency on updateField()'s internal branch condition for correctness of the fast-field cache.
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When using the standard CCDB loader, the magnetic field is initialised correctly.
However, when processing a second file from a different run, the
TGeoGlobalMagFieldinstance is deleted (AliceO2/Detectors/Base/src/Propagator.cxx
Line 131 in 10eb61e
mFieldis not reset (AliceO2/Detectors/Base/src/Propagator.cxx
Line 51 in 10eb61e
As a result, it becomes a dangling pointer and can return completely nonsensical magnetic field values (e.g. around 2e+22). The pointer therefore needs to be refreshed by calling
updateField. Furthermore,updateFieldonly updates the magnetic field if the pointermFieldis a nullptr. IfmFieldexists but points to invalid memory,updateFielddoes not update the magnetic field, so this logic also had to be fixed.Thank you @fchinu for reporting this bug!
@ddobrigk @dsekihat for your information!