SClang: PyrGC calls own methods in its constructor before fully initialised.

[JordanHendersonMusic]

Environment

• SuperCollider version: 3.14 - dev

Steps to reproduce

This isn't a problem in current use. However, #6261 introduces a limit on the number of objects to be scanned, which when set absurdly low (<1000) triggers the constructor of PyrGC to call its own member functions in the constructor before it is fully initialised, leading to a segfault. This is during the initialisation of the mProcess member (a PyrProcess).

Specifically:

The circular call into itself starts on this line,

supercollider/lang/LangSource/GC.cpp

Line 281 in 28a0b12

mProcess = newPyrProcess(g, mainProcessClass);

requiring mStack and g-> sp to be set, which don't happen until the next line or so.

This is less of a bug, because the behaviour will never be triggered, and more a case of incorrect design, albeit, quite a nuanced issue as dealing with an allocator that needs to call itself to allocate its component parts is circular.

As an improvement I suggest, either:

• the allocator should have some special methods, or even a boolean flag, that prevent it from attempting to collect while uninitialised — ugly, but simple,
• or, a different allocator should be used when initialising this object — this might not be possible,

Alternatively, this could just be ignored, but if the 'magic' number of the GC change, this issue might be triggered.