Lua returning output after subprocess - lua

Question

Working in lua, I have a table of key/value pairs
local fmtsToRun = {
name = function()
return configSubTable
end
}
Which could be 1 or more entries in length. I need to loop through each entry and run a subprocess (through some libuv C bindings).
With a normal for loop, the subprocess results from libuv return after the loop has finished running, leading to things showing up out of order. The result would be
Loop Start
Loop Entry 1
Job 1 starts
Loop Entry 2
Job 2 starts
Loop Ends
Job1 Returns
Job2 Returns
What I need to have is
Loop Start
Loop Entry 1
Job 1 starts
Job1 Returns
Loop Entry 2
Job 2 starts
Job2 Returns
Loop Ends
I've also tried writing my own version of pairs() to and using something like coroutines to handle the callbacks
for fmt, output in jobIterator(fmtsToRun) do
print('finished running', output)
end
local function jobIterator(tbl)
return coroutine.wrap(function()
local fmtConf, fmtName
fmtName, fmtConf = next(tbl, fmtName)
if nil~=fmtConf then
local conf = fmtConf()
local output = nil
-- wrapper util from Libuv library
local job = Job:new({
cmd = conf.cmd,
args = conf.args,
on_stdout = onStdout, -- process output
on_stderr = onStderr, -- process any error
on_exit = function()
coroutine.yield(fmtName, output)
end
})
job.send(conf.data)
end
end)
end
which leads to this error messages.
attempt to yield across C-call boundary
What would be the "right" way to wait for the job to finish and continue the loop while maintaining the correct order?

Answer 1

A better option was to manually control the flow and recursively call a function to step through the table one entry at a time.
local runner = {}
for _, output in pairs(fmtsToRun) do
table.insert(runner, output)
end
jobIterator(runner)
local function jobIterator(tbl)
local F = {}
function F.step()
if #tbl == 0 then
return
end
local current = table.remove(tbl, 1)
F.run(current)
end
function F.run(conf)
local output = nil
-- wrapper util from Libuv library
local job =
Job:new(
{
cmd = conf.cmd,
args = conf.args,
on_stdout = onStdout, -- process output
on_stderr = onStderr, -- process any error
on_exit = function()
-- do what you need with output
print(output)
F.step()
end
}
)
job.send(conf.data)
end
F.step()
end