Embedded Julia: Backslash hangs thread

General Usage
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1

I’m not entirely sure where the best place to put this question as I am new to this place and Julia in general. I’ve tried stack overflow but I think this is too specific for that.

I’ve embedded Julia into C# using the public C API. When I run the backslash command, execution stalls, and the process keeps consuming processor power. I’ve tried it both by running functions from imported modules and just running statements with jl_eval_string

Here are two examples of I can do that get’s it to hang.
Julia Module
function doStuff()
a = [1 2;3 4];
b = [4;6];
c = a\b;
end

In C# main function
jl_eval_string(“a=[1 2;3 4];”);
jl_eval_string(“b = [4;6];”);
jl_eval_string(“c=a\b;”);

I tried running it in a try/catch block to see if that would help, but it didn’t. Running the statements in the REPL or with a script executed from the command line work just fine. I’m not entirely sure what the differences are between running Julia from the command line and from C#.

Does anyone have an idea about what is going on here? I’ve tried using other lin alg functions and they work just fine.

2

Just a guess, but do you need to escape the backslash in \b ? That’s a valid escape sequence for C / C++ strings.

Try, perhaps, "c=a\\b" instead?

Ref: Escape sequences in C - Wikipedia

3

Oops, I wrote that in wrong. I’ve been using jl_eval_string("c=a\\b;"). I know that works because I’ve been able to change directories using the the double backslash.

Still doesn’t explain why it stops working in the Julia module though.

4

I can’t reproduce this on 0.6-rc3:

julia> include("mod1.jl")
Foo

julia> Foo.doStuff()
2-element Array{Float64,1}:
 -2.0
  3.0

mod1.jl is just your code wrapped with module Foo ... end.

5

I can’t reproduce from C on a tip-of-trunk build (on a mac). Please try from C. If you have a local build, comment out everything in examples/embedding/embedding.c between jl_init(); and int ret = 0; replace with:

    jl_eval_string("a=[1 2;3 4];");
    jl_eval_string("b = [4;6];");
    jl_eval_string("c=a\\b;");
    jl_eval_string("@show c");

Then in the examples dir run:

make
embedding/embedding

6

It works when run in the REPL. However, it happens when it’s run from C#.

Here is a more complete version of my code that has been heavily cut (I have a lot of testing code, and some rewritten stuff from julia.h for the garbage collector)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;
namespace TestCInCSharp{
    class Program{
        [DllImport("kernel32.dll", SetLastError = true)]
        static extern bool SetDllDirectory(string lpPathName);

        [DllImport("libjulia.dll", SetLastError = true)]
        public static extern void jl_init(string path);

        [DllImport("libjulia.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern IntPtr jl_eval_string(string input);
        //other dll imports here....
        //
        static unsafe void Main(string[] args){
            string p;
            string julia_path = @"C:\Users\schulk4\AppData\Local\Julia-0.5.2\bin";
            IntPtr module;
            SetDllDirectory(julia_path);
            jl_init(julia_path);
            //
            p = @"C:\\Users\\schulk4\\Documents\\Programming\\TestJuliaSim\\Assets\\test_julia.jl";
            p = "include(\"" + p + "\")";
            module = jl_eval_string(p); //holds module pointer? it appears to be so
            
            jl_eval_string("a=[1 2;3 4];");
            jl_eval_string("b=[4;6];");
            jl_eval_string("c=a\\b;");
         
            jl_atexit_hook(0); //tell Julia to shut down
            Console.ReadLine(); //pause so that output stays up
        }
    }
}
7

I assume you are talking about this, which is almost certainly not going to work as-written, and is most likely the cause of the problem:

8

As I said in my comment there, it is probably possible in principle but hooking in to pgc_stack like that is asking for trouble and probably provides no benefit (especially not if as-written you are allocating on the managed heap rather than using alloca).

9

Yes, but I stopped using the functions I wrote to try and see what was going wrong. That shouldn’t influence the code in the Julia function in the module though?

10

I’ve decided that I’ll try and do it the way that Ipython does it with the global array of references, and see if that works

11

Ok, if you are not doing the GC manipulation right now then that’s fine, I wasn’t sure based on how the intro to your example was worded.

Console.ReadLine(); //pause so that output stays up

Are you sure that work is actually happening? Try adding jl_eval_string("@show c"); – maybe it’s actually finished.

12

I just tried both C and C# (Visual Studio 2015) on Windows 10 against 0.5.2 release binary and it worked fine.

13

I made an entirely new project and copied only the things that I needed. I guess I’ll just work with this now. Thanks for your help

14

If there’s still an issue, please try some of the suggestions and report back – I’m happy to help debug further if I can find a way to reproduce it.