Object reference not set to an instance of an object error while using the TP in Mono

[tamizhvendan]

Hi @rspeele,

Thanks a lot for the awesome work.

Today, When I tried to use Rezoom type provider in my Mac using Mono (both 5.0.1 & 5.2.0) I am getting an "Object reference not set to an instance" error

To reproduce it, open the TypeProviderUsers.sln file in the Rezoom.SQL in either visual studio code or VS for Mac

/~/temp/Rezoom.SQL/src/TypeProviderUsers/TypeProviderUser.SQLite/Shared.fs(18,18): Error FS3033: The type provider 'Rezoom.SQL.Provider.Provider' reported an error: Object reference not set to an instance of an object (FS3033) (TypeProviderUser.SQLite)

SQLLite Type Provider

Postgres Type Provider

[tamizhvendan]

I guess it is something similar to this issue. Some internal code while initializing the type provider is causing the issue. I tried to attach debugger and troubleshoot but it didn't work out as we can't open more than one instance of VS for Mac :(

Is there any way that I can troubleshoot this to find the actual error?

[rspeele]

Hi,

Thanks for the bug report. A good way to troubleshoot it further would be to use the type provider from a .fsx script file and attach the debugger to fsi.exe. Rezoom.SQL.Provider has an example of this if you F5 it in debug configuration.

[tamizhvendan]

Thanks @rspeele

Unfortunately, it didn't work!

/~/temp/Rezoom.SQL/src/Rezoom.SQL.Provider/user.fsx(15,10): error FS3033: The type provider 'Rezoom.SQL.Provider.Provider' reported an error: Object reference not set to an instance of an object

mono_os_mutex_lock: pthread_mutex_lock failed with "Invalid argument" (22)
Stacktrace:

  at <unknown> <0xffffffff>
  at System.IO.KqueueMonitor.CleanUp () [0x00053] in <70507a44a84041d599bbfa8f3d0ea5b1>:0
  at System.IO.KqueueMonitor.DoMonitor () [0x00051] in <70507a44a84041d599bbfa8f3d0ea5b1>:0
  at System.IO.KqueueMonitor.<Start>b__5_0 () [0x00000] in <70507a44a84041d599bbfa8f3d0ea5b1>:0
  at System.Threading.ThreadHelper.ThreadStart_Context (object) [0x00014] in <c9f8153c41de4f8cbafd0e32f9bf6b28>:0
  at System.Threading.ExecutionContext.RunInternal (System.Threading.ExecutionContext,System.Threading.ContextCallback,object,bool) [0x00071] in <c9f8153c41de4f8cbafd0e32f9bf6b28>:0
  at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object,bool) [0x00000] in <c9f8153c41de4f8cbafd0e32f9bf6b28>:0
  at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext,System.Threading.ContextCallback,object) [0x0002b] in <c9f8153c41de4f8cbafd0e32f9bf6b28>:0
  at System.Threading.ThreadHelper.ThreadStart () [0x00008] in <c9f8153c41de4f8cbafd0e32f9bf6b28>:0
  at (wrapper runtime-invoke) object.runtime_invoke_void__this__ (object,intptr,intptr,intptr) [0x0004d] in <c9f8153c41de4f8cbafd0e32f9bf6b28>:0

Native stacktrace:

    0   mono                                0x000000010f9f6061 mono_handle_native_crash + 257
    1   libsystem_platform.dylib            0x00007fff8c5afb3a _sigtramp + 26
    2   ???                                 0x000070000cd9bfe0 0x0 + 123145517907936
    3   libsystem_c.dylib                   0x00007fff8c434420 abort + 129
    4   mono                                0x000000010fbcd591 mono_log_write_logfile + 353
    5   mono                                0x000000010fbe4740 monoeg_g_log + 208
    6   mono                                0x000000010fac63d1 mono_marshal_find_in_cache + 129
    7   mono                                0x000000010face23f mono_marshal_get_native_wrapper + 223
    8   mono                                0x000000010f9456f0 mono_jit_compile_method_inner + 384
    9   mono                                0x000000010f94884a mono_jit_compile_method_with_opt + 714
    10  mono                                0x000000010f9f866f common_call_trampoline + 1199
    11  mono                                0x000000010f9f8189 mono_magic_trampoline + 73
    12  ???                                 0x000000010fdad39e 0x0 + 4560966558
    13  ???                                 0x0000000118e3a5c9 0x0 + 4712539593
    14  ???                                 0x0000000118d8aa1e 0x0 + 4711819806
    15  ???                                 0x0000000118d8a7f5 0x0 + 4711819253
    16  mscorlib.dll.dylib                  0x00000001119cde11 System_Threading_ExecutionContext_Run_System_Threading_ExecutionContext_System_Threading_ContextCallback_object_bool + 33
    17  mono                                0x000000010f94c505 mono_jit_runtime_invoke + 2245
    18  mono                                0x000000010fb4dd48 do_runtime_invoke + 88
    19  mono                                0x000000010fb19a9e start_wrapper + 766
    20  libsystem_pthread.dylib             0x00007fff8c5b993b _pthread_body + 180
    21  libsystem_pthread.dylib             0x00007fff8c5b9887 _pthread_body + 0
    22  libsystem_pthread.dylib             0x00007fff8c5b908d thread_start + 13

Debug info from gdb:

(lldb) command source -s 0 '/tmp/mono-gdb-commands.TCzxrT'
Executing commands in '/tmp/mono-gdb-commands.TCzxrT'.
(lldb) process attach --pid 32058
error: attach failed: unable to attach

The application was terminated by a signal: SIGHUP

[tamizhvendan]

I tried to troubleshoot this using printfn as suggested.

For this code in user.fsx

type QueryWithNullablePar = SQL<"""
    select * from Users u
    where u.Name is @name
""", "user-migrations">

I put printfn in these places

Provider.fs

do
        printfn "initializing #2" // <----

        let tys = [ sqlTy; modelTy ]
        tmpAssembly.AddTypes(tys)
        this.AddNamespace(rootNamespace, tys)
        modelCache.Invalidated.Add(fun _ -> this.Invalidate())
        this.Disposing.Add(fun _ -> modelCache.Dispose())

        printfn "init success" // <----

    static do

        printfn "initializing #1" // <----

        System.AppDomain.CurrentDomain.add_AssemblyResolve(fun _ args ->
            AssemblyResolver.resolve args.Name |> Option.toObj)

TypeGeneration.fs

let generateSQLType (generate : GenerateType) (sql : string) =
  printfn "generating SQL Type" // <----
  // ...
  provided.AddMember <| generateCommandMethod generate commandEffect commandType commandCtorMethod

    printfn "generated SQL type" // <----

    provided

Here is the output that I got

initializing #1
initializing #2
init success
generating SQL Type
generated SQL type

/Users/tamizhvendan/TamizhWorks/temp/Rezoom.SQL/src/Rezoom.SQL.Provider/user.fsx(15,29): error FS3033: The type provider 'Rezoom.SQL.Provider.Provider' reported an error: Object reference not set to an instance of an object

I guess I am able to troubleshoot it using printfn. It would be helpful if you can help me in placing the print statements in the codebase to identify the root cause

[rspeele]

I haven't the slightest clue where that NRE might be coming from, but I think using this event handler to do some logging might help you obtain a useful stack trace:

https://msdn.microsoft.com/en-us/library/system.appdomain.firstchanceexception.aspx

[tamizhvendan]

Unfortunately, it didn't trap the exception!

Hi @ovatsus, @andrevdm, Can you folks help here? it is similar to the Fsharp.Data issue but we couldn't able to debug/troubleshoot it

[tamizhvendan]

@rspeele Is it because of the error being discussed in SO

[rspeele]

Leaving a note here that this might fix it:

https://github.com/fsprojects/FSharp.TypeProviders.StarterPack/issues/121

I'm on Windows only at the moment and not able to quickly repro the original issue so I can't tell if upgrading the ProvidedTypes.fs helps at all.

[Swoorup]

I tested on ubuntu with Mono 6.0.0 Preview and 5.20.1 Stable (5.20.1.19). Can confirm we still run into the same issue.