Cannot resume non-suspended coroutine, DataStore & xpcall()

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#1

Since DataStore OnUpdate is broken I have to come up with another way to check for a New Place Version with Datastore so I did, but the problem is that I keep getting this error
cannot resume non-suspended coroutine

I’m not sure why but I think it’s because of the xpcall() see code below

Code 
-- PlaceVersion DataStore --
if not RunS:IsStudio() then
	local GameDataStore = DataStoreService:GetDataStore('Name','Scope')
	local Saved_PlaceVersion,Result
	local Default_WaitTime = 60
	local Extra_WaitTime = 0
	local function GetANDCompare_PlaceVersions_Func()
		local Success = pcall(function() Saved_PlaceVersion = GameDataStore:GetAsync("PlaceVersion") end)
		if Success and Saved_PlaceVersion then
			Result = Current_PlaceVersion == Saved_PlaceVersion and 'Lastest_Version' or Current_PlaceVersion < Saved_PlaceVersion and 'Outdated_Version' or Current_PlaceVersion > Saved_PlaceVersion and 'New_Version'
			print('Time',tick())
			return
		end
		wait(Default_WaitTime)
	end
	local function CheckForPlaceVersionUpdate_Func()
		while wait(5) do
			if DataStoreService:GetRequestBudgetForRequestType(1) >= 5 and xpcall(GetANDCompare_PlaceVersions_Func,GetANDCompare_PlaceVersions_Func) then
				if Result == 'Outdated_Version' then
					break
				elseif Result == 'New_Version' then
					GameDataStore:SetAsync("PlaceVersion",Current_PlaceVersion)
					Extra_WaitTime = 600
				elseif Result == 'Lastest_Version' then
					Extra_WaitTime = 300
				end
			end
			print(Result)
			Result = nil
			wait(Default_WaitTime+Extra_WaitTime)
		end
	end
	spawn(CheckForPlaceVersionUpdate_Func)
end

Output >>
https://gyazo.com/61c24d104bf0d0ec03ba46504d981481
https://gyazo.com/4153563d0ac19705cd4b5dd72227c8f0
https://gyazo.com/b28b8717f416c81278a295581415f7da

Testing xpcall() Behavior 
local X = 0

local function Err_Func()
	X = X + 1
	print(time())
	error('Hi There')
end

for i = 0, 10 do
	xpcall(Err_Func,Err_Func)
end

print(X)

Output of X >> 2442

#2

You cannot yield in xpcall. Re-implement xpcall as the following:

local function xypcall(successProc, failureProc, ...)
	-- Store it in a table to get all return values
	local call = {ypcall(successProc, ...)}
	
	-- Check if the pcall failed to call the failure proc
	if not call[1] then
		call = {ypcall(failureProc, select(2, unpack(call)))}
		-- If the proc to call when failing errored, return "error in error handling"
		if not call[1] then
			return false, "error in error handling"
		end
		return false, select(2, unpack(call))
	end
	
	return true, select(2, unpack(call))
end

…or if you want to be less verbose than I am, just use ypcall and check if the success return is true or not.

#3

This is not a correct alternative. The main point of xpcall is that the error handler is called just after the error, allowing the handler to retrieve a stack trace via debug.traceback. This is otherwise impossible without using a custom error function to intercept the error beforehand.

pcall also disallows error types other than strings, while xpcall allows anything.

2 Likes
#4

That’s true, although I think my code is good enough for most use cases for it.

#5

Cool I like how you implemented your own xypcall()

I don’t understand the problem tho,

Does xpcall() trigger the Err handler function until it succeeds or just once?

Why does it seems like it’s being triggered a lot? see Testing xpcall() Behavior

#6

We can’t.

> xpcall(function() error() end, function() wait() end)
13:19:59.263 - attempt to call a nil value
13:19:59.423 - cannot resume non-suspended coroutine (x220)

> xpcall(function() wait() end, function() print("im here") end)
im here
13:20:13.145 - attempt to call a nil value

As for the xpcall behavior in your post, I’m not sure.

#7

…I thought I could trust @Crazyman32 I am devastated.

Joking aside, is that a bug or supposed to happen? I thought that Roblox made some changes a few months ago.

#8

Yielding in pcalls (that aren’t ypcall) just seems to be broken in many ways, it’s not documented on the Lua wiki if that’s what you’re asking.

#9

Hmm is that a bug? I know for sure pcall can yield. ypcall was added before that was the case, and then they changed pcall. I see no reason why xpcalls behavior shouldn’t be changed too.

#10

You can yield in a pcall (which means you can change my code to pcall instead of ypcall), but not in an xpcall.

#11

Yes I understand that, but that’s why I would assume that xpcall should behave the same

1 Like