Problem 1706

In Version 10.1 to reduce memory consumption a locking of mutex in GPS was introduced in G4SingleParticleSource::GeneratePrimaryVertex (see attachment lock-where.png). When primaries are of low energy and setup is simple the generation of primaries is highly penalized with a moderate number of threads (>8) because the mutex plays a major role.

As an example, in case of 24 threads, only 4 threads are efficiently used (see compare.png, where the blue bars represent the time spent with a given number of threads running for 10.1 and the yellow bars represent the same quantity for 10.0).

A strategy to remove the lock is needed, because this can dramatically impact medical applications, however this is not completely trivial as it requires understanding concurrency issues in the underlying classes.

Andrea