Race condition when displaying MantidMatrix of updating workspace

[mantid-builder]

Original Reporter: Russell Taylor

This has manifested itself as a segmentation fault when displaying an EventWorkspace during a live data run, but I think it's a possible problem (if less likely) with a Workspace2D as well.

We presumabely need to read-lock the workspace.

Here's a stack trace of the crash:

Mantid::DataObjects::TofEvent::tof() at Events.h:102    
Mantid::DataObjects::EventList::generateCountsHistogram() at EventList.cpp:2,059    
Mantid::DataObjects::EventList::generateHistogram() at EventList.cpp:1,986  
Mantid::DataObjects::EventList::constDataY() at EventList.cpp:1,536 
Mantid::DataObjects::EventList::dataY() at EventList.h:278  
Mantid::API::MatrixWorkspace::readY() at MatrixWorkspace.h:172  
MantidMatrixModel::data() at MantidMatrix.cpp:1,467 0x9b8372    
MantidMatrixModel::data() at MantidMatrix.cpp:1,517 0x9b869f    

[mantid-builder]

This issue was originally trac ticket 5462