I also need a random number generator, but that's a separate issue --- except for the matter of how to seed the random number generator differently on each of the interpreters, which does go back to the same problem; ... and yes, a portion of the seed does need to be unpredictable,

Yes, it was your earlier mention of your requirement for a cryptographic RNG that I was addressing.

but we already have /dev/urandom for that, so...).

I looked for that on my system and got:

c:\test>dir /s /dev/urandom
Parameter format not correct - "dev".
[download]

But seriously, that isn't portable even across *nix-like systems, let alone further afield.

TSC, which I hadn't heard of before (thanks), unfortunately appears to be x86-specific, and perhaps even Intel-x86-specific,

All recent AMD x86 processors and all their x64 processors also have the rdtsc instruction.

And pretty much every other modern processor has an equivalent.

• ARM call it the Cycle Count Register.
• UltraSPARC call it the Performance Counter Register(s)
• IBM PowerPC has gazillions of them, but the first is pretty much equivalent