I need some embeddable language for tasks similar to query execution in mongodb. Language should be fast and it should have both JIT and interpreter (for frequent scripts that JIT-compiled and for one-time-run scripts too), should have in-memory runtime that I populate with specific API functions (or classes, whatever) by hand (and nothing "built-in" else like gettime, thread spawning or similar), it should have C API and it should work on ARM (MIPS also would be nice), not too big footprint also would be nice (but this is not critical).
I have two candidates:
I have not experienced embedding languages into C projects before so I have a few questions: recently there was a rumor that V8 is not thread-safe, is this problem still exists? If so, where that lack of thread-safe can cause problems?
Also I would be glad if anyone suggested embeddable language which is more suitable for my requirements (except lua, I can't find any advantages in comparison with js except smaller footprint about what I don't care).
I'm not sure how SpiderMonkey's multithreading embeddability compares to V8's, but I do know that it's possible to do with SpiderMonkey -- we have a few multiprogramming embedders on dev.tech.js-engine that you may want to post followup questions to.
Our web workers implementation in the browser uses one runtime instance per worker (you can multiply instantiate the runtime in a single process) -- we've moved away from an multithread-safe single-runtime approach over the past few years because it's unnecessary for the web and adds a significant amount of complexity to the engine.
An alternative to multiprogramming is also the asynchronous, select-based, run-to-completion approach a la node.
A nit: I don't think an interpreter is really a requirement of yours -- your requirement is fast start up times for one-off code. SpiderMonkey has an interpreter and V8 does not, but V8 has a fast-code-emission (which we tend to call "baseline") JIT compiler that offers comparable performance in that area. That capability is an important requirement for JS on the web in general. :-)