Crash when setting MultiThreaded.MaxCores to > number of machine cores

[mantid-builder]

Original Reporter: Russell Taylor

Witnessed when working with WISH data on both my Mac (2 cores) and PC (12 cores). In the former case it crashes (100% of the time) when MultiThreaded.MaxCores is 3 or greater, in the latter case if it's 14 or more.

MultiThreaded.MaxCores is used in Mantid to call the OpenMP omp_set_num_threads directive. In principle, it should be possible to have more threads than cores, so I don't know why it suddenly crashes when this threshold is breached when we've never (afaik) seen a problem in this part of the code otherwise. One suggestion has been whether it's to do with the stack size, but a quick play with setting the OMP_STACKSIZE environment variable had no apparent effect.

The obvious and easy solution is to prevent the setting of the number of threads to greater than the number of processors.

Linux stack trace:

boost::detail::sp_counted_base::use_count() at sp_counted_base_gcc_x86.hpp:165 0x997c20 
boost::detail::shared_count::use_count() at shared_count.hpp:269 0x997c4d   
boost::detail::shared_count::unique() at shared_count.hpp:274 0x7ffff7c2d5fa    
boost::shared_ptr`<Mantid::Geometry::Detector>`::unique() at shared_ptr.hpp:432 0x7ffff755bbd4  
Mantid::Geometry::ComponentPool`<Mantid::Geometry::Detector>`::getIndexInCache() at ParComponentFactory.cpp:78 0x7ffff755b2ac   
Mantid::Geometry::ComponentPool`<Mantid::Geometry::Detector>`::create() at ParComponentFactory.cpp:46 0x7ffff755ab96    
Mantid::Geometry::ParComponentFactory::createDetector() at ParComponentFactory.cpp:118 0x7ffff755a1de   
Mantid::Geometry::Instrument::getDetector() at Instrument.cpp:412 0x7ffff74ef755    
Mantid::Geometry::Instrument::getDetectors() at Instrument.cpp:481 0x7ffff74efe7c   
Mantid::API::MatrixWorkspace::getDetector() at MatrixWorkspace.cpp:734 0x7ffff6f9ead5   
Mantid::Algorithms::ConvertUnits::convertViaTOF() at ConvertUnits.cpp:422 0x7fffdeaa4685    

Mac stack trace:

Thread 8 Crashed:
0   libMantidGeometry.dylib         0x0000000100f6ec39 Mantid::Geometry::ParComponentFactory::createDetector(Mantid::Geometry::IDetector const*, Mantid::Geometry::ParameterMap const*) + 713
1   libMantidGeometry.dylib         0x0000000100f20b52 Mantid::Geometry::Instrument::getDetectors(std::set`<int, std::less<int>`, std::allocator`<int>` > const&) const + 178
2   libMantidAPI.dylib              0x0000000101294573 Mantid::API::MatrixWorkspace::getDetector(unsigned long) const + 803
3   libMantidAlgorithms.dylib       0x00000001192cbedc Mantid::Algorithms::ConvertUnits::convertViaTOF(boost::shared_ptr`<Mantid::Kernel::Unit const>`, boost::shared_ptr`<Mantid::API::MatrixWorkspace>`) + 5052
4   libiomp5.dylib                  0x0000000104d45b53 __kmp_invoke_microtask + 147
5   libiomp5.dylib                  0x0000000104d26195 __kmpc_invoke_task_func + 181
6   libiomp5.dylib                  0x0000000104d2204a __kmp_launch_thread + 490
7   libiomp5.dylib                  0x0000000104d45f5d __kmp_launch_worker(void*) + 333
8   libSystem.B.dylib               0x00007fff83bdcfd6 _pthread_start + 331
9   libSystem.B.dylib               0x00007fff83bdce89 thread_start + 13

[mantid-builder]

This issue was originally trac ticket 3834