content_by_lua+require+coroutine throws attempt to yield across C-call boundary

[Aleksey Akulovich]

Hello.

I have nginx 1.6.0 + luajit 2.0.2 with config:

# nginx.conf
lua_package_path '/path/to/lua/?.lua;;';
location / {
    #content_by_lua_file '/path/to/lua/foo.lua'; # works fine
    content_by_lua 'require("foo")'; # fail
}

# foo.lua
local function c()
    return coroutine.wrap(function()
        for i = 1, 10 do
            coroutine.yield(i)
        end
    end)
end

for v in c() do
    ngx.say(v)
end

An error occurs "lua entry thread aborted: runtime error: attempt to yield across C-call boundary".

[Yichun Zhang]

@atercattus This is a known limitation in LuaJIT (and the standard Lua 5.1 interpreter) that the require() builtin is currently implemented as a C builtin across which you cannot initiate a yield. A work-around is to put your coroutine operations in a function in your Lua module and let the caller call your function explicitly after require(), for example,

local foo = require "foo"
foo.go()

or more concisely:

require("foo").go()

And your for v in c() do ... end loop should be in the function named go (or something else) in your foo.lua file.

Mike Pall is going to reimplement the require builtin with LuaJIT bytecode in LuaJIT and by that time this limitation will get removed. You can prod him on the luajit mailing list and/or sponsor him to work on it directly ;)

[Aleksey Akulovich]

Sponsorship of development is a good option.
Thanks.

[Pierre-Yves Gérardy]

FWIW, https://github.com/pygy/require.lua implements require in plain Lua, sidestepping the problem.

I'll test it more thoroughly tomorrow, but AFAICT, it works like the original.

You can sponsor me retroactively, if you want ;-)