Bootstrap.cpp: Relinquish python's GIL before calling executeRun to allow python algs in MT mode
I assume this needs a bit of discussion in a ATLAS Core SW meeting and/or a Gaudi meeting.
Background: ATLAS Data Quality relies on post-processing of histograms implement as python algorithm. When running as online monitoring at P1, these python post-processing is invoked as algorithm in the event loop to present the shifter in the control room real-time histograms. Running this job in MT-mode creates a deadlock between the python-code doing the configuration and invoking the run-method of the c++-application and python code executed as algorithm in a different thread. The call chain is: python -> C++ spawning threads -> python.
The changeset here solves this problem by invoking the macro Py_BEGIN_ALLOW_THREADS just before calling IEventProcessor::executeRun.