Lua Academy · Lesson

Coroutine Status

Check coroutine state with coroutine.status: running, suspended, dead.

Four Coroutine States

Coroutines have four possible states: suspended (created or yielded, waiting to run), running (currently executing), normal (paused to let another coroutine run), and dead (finished or errored). Query with coroutine.status(co).

local co = coroutine.create(function()
  print(coroutine.status(coroutine.running()))  -- running
  coroutine.yield()
end)

print(coroutine.status(co))  -- suspended
coroutine.resume(co)          -- prints: running
print(coroutine.status(co))  -- suspended
coroutine.resume(co)
print(coroutine.status(co))  -- dead

The "normal" State

A coroutine enters the "normal" state when it resumes another coroutine. It's not running (the other coroutine is), but it's not suspended either — it's waiting for the resumed coroutine to yield. This state is rare but important to understand for complex coroutine graphs.

local inner, outer

inner = coroutine.create(function()
  print("outer status:", coroutine.status(outer))  -- normal
  coroutine.yield()
end)

outer = coroutine.create(function()
  coroutine.resume(inner)
end)

coroutine.resume(outer)
-- prints: outer status: normal

All lessons in this course

← Back to Lua Academy