Re: lua_resume and a C-function as the main coroutine function problem

[Mark Feldman <mfeldman@...>]

Roberto Ierusalimschy wrote:

It is forbidden to resume a C function. The manual should mention that.
Thanks for the report.

Is this by deliberate design? Or by virtue of the fact that it hasn't been deliberately implemented? As far as I can gather the lua_resume function works by re-using the function pointer on the top of the stack from the previous call, so it's possible (in 5.1.4 at least) to yield C functions so long as you ensure that this value is maintained. You also have to handle the resume logic yourself since there's only one entry point:

== begin code ===
    #define YIELD(func) {lua_pushcfunction(L, func); lua_yield(L, 1); return -1;}

    // C-function with co-routine support:
    static int foo(lua_State *L)
    {
        static int instr_num = 0;
        switch (instr_num++)
        {
            case 0: printf("Hello World!\n"); YIELD(foo);
            case 1: printf("Goodbye World!\n"); YIELD(foo);
            default: return 1; // coroutine dies
        }
    }


    // initialize it and assign it to the "foo" global
    lua_pushcfunction(L, foo);
    lua_setglobal(L, "foo");

    -- lua code to call it
    local co_foo = coroutine.create(foo)
    coroutine.resume(co_foo)                --> Hello World
    coroutine.resume(co_foo)                --> Goodbye World
== end code ===

Needs some extra logic to handle multiple calls but you get the idea. The switch statement allows you to resume anywhere in your function while still allowing each "instruction" to fall through to the next e.g. for conditional yields.

No?

Mark Feldman

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