During development of radiosity code for POV-Ray 3.7, I encountered frequent
segfaults on an AMD64 QuadCore Debian "Etch" Linux system with particular
scenes. Observation strongly suggests that these segfaults are related to the
combination of radiosity and photons.

The exact nature of the underlying problems still remains unknown. They may or
may not be influenced by the way the POV binaries were built; however, they are
a strong indicator that there is an inherent instability in POV 3.7 regarding
the Radiosity + Photons combo.

As (A) the radiosity code has been thoroughly examined for thread-safety, (B)
activating photons does in no way change the behavior of the radiosity
algorithm nor (C) the way it is called, and (D) the radiosity code calls photon
code only indirectly, I take the segfaults as an indicator that there is a yet
undiscovered issue in the photons code, possibly regarding thread-safety
(access to the photons cache would be a hot candidate).

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