HOWTO: Inter-plugin communication

[xoft]

Yes, on its own it's not slow, but it causes lock convoys - each such call must lock an additional plugin's critical section. If the plugin is busy, with lots of hooks, this will become costly.

[NiLSPACE]

Is the cPlugin::Call function able to parse functions as parameter?

[xoft]

No, it cannot, mainly because functions in Lua are really closures - they take with them the local values of their containing functions and are able to modify those; this cannot be safely ported to another Lua state structure. Consider the following example:

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function FnOuter(ParamOuter)   local VarOuter = 10;   local FnInner = function(ParamInner)     local VarInner = VarOuter + 1;  -- It can read FnOuter's local variables     VarOuter = VarOuter * 3;  -- It can modify them     local VarInner2 = ParamOuter + 1;  -- It can even read FnOuter's parameters   end   SomeOtherFunction(FnInner);  -- Perfeclt valid Lua code, SomeOtherFunction() can call FnInner however it wants end

[FakeTruth]

Is the cPlugin::Call function able to parse functions as parameter?

No, you can however pass a function name and a plugin instance, so the other plugin can call the function on your plugin.

[NiLSPACE]

No, you can however pass a function name and a plugin instance, so the other plugin can call the function on your plugin.

Yea I know but I hoped you could use a local function as parameter.

[NiLSPACE]

I just realized that you can parse a function as a string and then use the loadstring() function to execute it. for example:

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------------------------------------------------ --Plugin 1 local Callback = [[     return type(500) ]] Plugin:Call("Example", Callback)     ------------------------------------------------ --Plugin 2 function Example(Callback)     local Function = loadstring(Callback)     if Function then --If the string is loaded correctly then execute it. Otherwise it's a nil value.         Test = Function()     end     print(Test) end

now Test should be equal to 'number'.

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Hmm wait now i'm suddenly unsure if it works..

[xoft]

That might work but is pretty much useless. Such a function won't have the upvalues, so it won't see neither the first plugin's globals nor the locals. Consider this example:

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-- Plugin 1: function CallMe() ... end g_UseMe = 1; local SomeVar = 2;   local Callback = [[   g_UseMe = 2;   SomeVar = 3;   CallMe(); ]] Plugin2:Call("Executor", Callback); -- The call has failed inside Plugin2, but that doesn't propagate here -- However, g_UseMe is still 1, SomeVar is still 2 and CallMe() hasn't been called.     -- Plugin 2: function Executor(Callback)   local Function = loadstring(Callback);   Function();  -- will set Plugin2's globals g_UseMe to 2 and SomeVar to 3 and then fail with message "CallMe not defined" end;

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I'm not sure now whether Plugin2 will fail on the actual execution, or if the loadstring() will already complain about the undefined function. But the end result is the same - the callback just cannot access Plugin1's data in any way.

[NiLSPACE]

Yea I posted it and then suddenly I was like: "Wait... It's nog going to work isn't it..."