Pico-8 coroutines are occasionally dead

Question

I was trying to replace a for-loop with coroutines to move the stars:

--fine
function _update()
 for c in all(boids) do
  move_boid(c)
 end
end

--broken
function _update()
 for c in all(boids) do
  coresume(cocreate(move_boid),c)
 end
end

Notice that a fixed number of stars are frozen (I'm pretty sure the number is fixed):

But why? How can I handle this? The complete code is on itch.

Answer 1

Thanks for @Vald and @Egor's comments. Seems the problem is caused by "too-long coroutines" to finish in a PICO-8 cycle. So the solution is that I store unfinished coroutines in a table and resume them if not finished. But somehow the movement is changed, kinda like "lost frame".

Here's my edited code:

function _init()
 -- code
 cors={}
end

function _update()
 for i=1,#boids do
  local co=cocreate(move_boid)
  local c=boids[i]
  add(cors,co)
  coresume(co,c)
 end
 for co in all(cors) do
  if (co and costatus(co)!="dead") then
   coresume(co)
  else
   del(cors,co)
  end
 end
end

And also modify the calculation function, adding a new line in the middle:

function move_boid(c)
 -- code
 yield()
 -- code
end

Just to yield before it's completed.

---

Update: another way to do it is reusing coroutines.

function _init()
 -- code
 -- create coroutines
 cors={}
 for i=1,#boids do
  local co=cocreate(move_boid)
  local c=boids[i]
  add(cors,co)
  coresume(co,c)
 end
end

function _update()
 foreach(cors,coresume)
end

-- and wrap the move function with a loop
function move_boid(c)
 while true do
  -- code
  yield()
  -- code
  yield()
 end
end