Hey guys I m making Kotlin Multiplatform work on Windows now

Question

Hey guys I m making Kotlin Multiplatform work on Windows now but I have an issue of calling Kotlin back from C++ Here is my use case I want use socket io client cpp to connect to a SocketIO server and get a callback when it connects successfully But the callback is not invoked on main thread I do notice the note on the C Interop page calling `kotlin native initRuntimeIfNeeded ` in my kotlin code before I connect to server but it still crash my program If I fire the callback on main thread e g APP C++ code calls `kotlinTestFunc` which calls `cppSocketIOConnect` and fire the callback directly inside `cppSocketIOConnect` it works fine Do I miss something

Artyom Degtyarev [JB] · Answer

Can you share more details on the error

Piasy · Answer

Sorry visual studio just says Exception thrown ```Exception thrown at 0x004FEFB0 in WindowsExample exe 0xC0000005 Access violation executing location 0x004FEFB0 ``` I write it to crash dump and analyze it with dbghelper but the stack also doesn t give helpful message the attachment is the full analyze output

Piasy · Answer

Sorry the previous attachment may contain duplicate content please check this one thanks

Piasy · Answer

Oh sorry < Artyom Degtyarev JB > I find the reason It turns out that I do the wrong capture in C++ lambda how stupid am I Here is the working code snippet ```void SioOn void sio SIOListener2 listener reinterpret cast lt sio client gt sio gt set socket open listener = std string const amp nsp listener ``` Previously I capture it by reference ` amp `

Piasy · Answer

Oh btw do you know how to create ` pdb` when compile kotlin code to ` dll` on windows < Artyom Degtyarev JB >

Artyom Degtyarev [JB] · Answer

Seems like there is no such option for now The best you can get here is a dwarf compatible debug info see here <https github com JetBrains kotlin native blob master DEBUGGING md>

Piasy · Answer

Thanks I ll check it out

Piasy · Answer

Hi < Artyom Degtyarev JB > I have a follow up question in the non main thread case I want to pass some data when the callback is fired in C++ code e g a integer but if I access the `Int` in kotlin code my program crashed with error `Exception thrown at 0x6514A0E9 AvConf dll in WindowsExample exe 0xC0000005 Access violation reading location 0x00000020 ` if I don t access the integer it works fine if I fire the callback directly in main thread it also works fine

Artyom Degtyarev [JB] · Answer

I m sorry but I m missing something here Are you sending a Kotlin s `StableRef` to the callback or it is a C++ `int` that the Kotlin function takes as input

Piasy · Answer

It is a C++ `int` that the Kotlin function takes as input Here is my C++ code ```typedef void SIOListener int void SioOn void sio const char event SIOListener listener reinterpret cast lt sio client gt sio gt set socket open listener = std string const amp nsp listener 0 ``` Here is my kotlin code ```private fun SioListenerFunction2 len Int Logging error SIO SioListenerFunction2 Logging error SIO len $len NKBundle SioOn socket event staticCFunction SioListenerFunction2 ``` If I don t log `len` param or if I invoke `listener` directly it works fine

Piasy · Answer

btw the `socket` variable is created by a C++ function so don t worry about it

Artyom Degtyarev [JB] · Answer

Try to call `initRuntimeIfNeeded ` here before logging

Artyom Degtyarev [JB] · Answer

Also I got some suspicions about passing value like that maybe one should create a parameter with default value like ``` = std string const amp nsp int zero = 0 listener zero ``` but it s just a guess

Piasy · Answer

Hi < Artyom Degtyarev JB > calling `initRuntimeIfNeeded ` does the magic So the note in C Interop page means it should be called inside the callback right And regarding your comment on C++ code actually passing 0 back is only for test purpose there shall be more data from C++ and the `int` is the length of an array Thank you very much