Segfault in ParameterMap::asString

[Harry Jeffery]

mat_ws = Load(Filename='MAP05935_ei34.nxspe')
LoadInstrument(mat_ws, InstrumentName='MAPS')
SaveNexusProcessed(mat_ws, Filename="this_will_crash.nxs")

This script crashes Mantid, with a sefault in ParameterMap::asString.

[Nick Draper]

This is because the nxspe file creates and in memory instrument, but this will not match the detector numbers etc within the intsrument being loaded.

It is not frequent normal behaviour to do this in a reduction and analysis workflow.

Fixing the crash would be good, but not high priority.

[Harry Jeffery]

Refs #11749 Fix segfault

Changeset: 139cf95dac52f5217fcb7933960f25748a938760

[Harry Jeffery]

Refs #11749 Don't risk touching someone elses pmap

Changeset: 54af10ae56ad741df9416452bc6c9a846937c54c

[Harry Jeffery]

This is being verified as ​pull request #751.

[Harry Jeffery]

Refs #11749 Fix segfault in systemtest

Changeset: 99a6efbac324d459e2517bba7f099c87b552f513

[Harry Jeffery]

The reason the system test was segfaulting was because it fetched const reference to the parameter map and *then* performed setInstrument, which replaces the internal parameter map pointer. The reference is then to freed memory, which is not good™. The easy fix in this case is just to get the reference after, but it's a very easy mistake to make again.

We should have a good think about what we return from instrumentParameters to prevent this happening again, as it's a nasty error that's not immediately obvious. My first reaction is to instead have instrumentParameters return a ParameterMap_const_sptr&, so that the reference stays up to date if the internal parameter map changes.

[Harry Jeffery]

The windows build failure is unrelated. isis-ndw1185 is playing up.

[Owen Arnold]

As this is Core and as it's a little tricky to get into the state where this becomes an issue so close to the release. I'm moving this to 3.5.

[Harry Jeffery]

@mantid-roman [This](​https://github.com/mantidproject/mantid/blob/11749_segfault_in_parametermap_asstring/Code/Mantid/Framework/API/src/ExperimentInfo.cpp#L167-L191) is the currently problematic area.

If you set the instrument after fetching this reference you have a reference to freed memory, causing a crash when used.

This originally comes in in 5e030f1

Do you know why this needs to be copy-on-write? See [this comment](​https://github.com/mantidproject/mantid/pull/751#issuecomment-102070166) for my suggestion for resolving this. Returning a reference to the shared pointer means that our reference keeps pointing to the right thing if the shared pointer changes.

[Roman Tolchenov]

Merge pull request #751 from mantidproject/11749_segfault_in_parametermap_asstring

Fix parameter map segfault

Full changeset: ​54d45ad608deb0611cb025f7db4b65236c27f06f

[Stuart Campbell]

This ticket has been transferred to github issue ​12587