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I'm making a programming game in C++ and Qt, but have a unique constraint as far as my choice in engines go; because it's possible that the player may write code that loops infinitely or takes a long time to run, I need to be able to terminate a scripting engine's execution at any time. I asked a question about this on StackOverflow yesterday, and unfortunately there's no way to kill a thread in C++ without potentially causing resource problems (locks not being released, memory leaks, etc.).

I was advised that I need a scripting engine that allows me to terminate scripts at will without jeopardizing the player's session. What options do I have, subject to these requirements?

  • It must be embeddable in a C++ application.
  • It must work on Windows, Mac, Linux, and Android.
  • It doesn't need to be a mainstream language like Python, but it must be teachable to someone entirely new to programming.
    • Haskell, Scheme, Prolog, etc. are right out unless you can convince me that they would be good first languages for an 11-year-old to learn.
  • I need to be able to stop a script's execution at any time.
    • I can't kill the thread itself, so why not kill the scripting engine?
  • I should have full control over the scripting context (e.g. what objects/functions/types are available).
  • Qt integration would be nice, but is optional (I can make my own wrapper).
  • It doesn't need to be very fast -- the player's code will run repeatedly, but no more than once every half-second or so.
  • I must be able to call C++ functions from this scripting engine, and I must be able to call functions written in this scripting language from C++.
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  • Actually, you might not need the ability to terminate the scripting engine at will. It might well be enough to be able to signal it that you want a long-running script terminated; or you could have it use time-outs internally, like Javascript's setTImeout()
    – einpoklum
    Commented Jul 16, 2016 at 6:52
  • Also remember that you can instruct users to write simple scripts, using a small subset of the scripting language's grammar - and if they try writing something more complex, it's up to them. And a final note - check out what existing FOSS games use (0 A.D., Battle for Wesnoth, Cave Story) - at leasy some of them use a scripting engine, and you can get inspiration regarding how to use it as well.
    – einpoklum
    Commented Jul 16, 2016 at 6:57

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You might want to try Lua.

  • It is embeddable in C or C++

  • It is portable (works on all platforms that have a C compiler)

  • It is a rather easy language

  • You can call into Lua from C++ and the other way round (even nested multiple times)

  • You have full control over which functionality/objects/... are provided to the scripts

  • From my understanding it should be feasible to terminate an executing Lua engine in a multithreaded environment

If you want to stay entirely inside C++, you might be interested in luabind.

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  • @JesseTG: The Battle for Wesnoth uses Lua extensively.
    – einpoklum
    Commented Jul 16, 2016 at 6:54
  • Many games do: e.g. WoW (for user addons) and Civilization V, just to name 2 AAA titles from the top of my head
    – hoffmale
    Commented Jul 16, 2016 at 8:17
  • If Lua runs under a C++ thread, and you terminate it, you terminate the C++ thread and violate the OP's original objection. Why is this an answer?
    – Ira Baxter
    Commented Aug 30, 2016 at 4:49

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