ccall()-ed function output not shown until execution is finished

[cbecker]

I am not sure how to enable logging of stdout for ccall()-ed libraries. For example, lets make ``test.c` be

#include <stdio.h>

void test()
{   int i=0;
    for (i=0; i < 10; i++)
    {
        printf("hehe\r\n");
        fflush(stdout);
        system("sleep 0.5");
    }
}

compite with gcc -shared test.c -o test.so -fPIC, and then call it from IJulia (console or qtconsole):

ccall( (:test, "./test.so"), None, () )

Instead of seeing a series of 'hehe', separated by a 500ms pause, I see nothing at all with console, while I see the whole bunch of stdout appearing instantly once the ccall returns with qtconsole. It looks like something related to how stdout is handled, maybe close to #23

Thanks.

[stevengj]

While your C code is running, the IJulia kernel is not running; there is no way for it to send stdout to the front-end until you give IJulia some cycles.

I don't see any way to fix this, short of having your C code call the the equivalent of yield() occasionally in the julia jl_* API.

[cbecker]

Thanks Steven. That is an option in my case, because I generally link to libjulia.so, so that would help. It gets trickier with other libraries of course.

[stevengj]

It would be nice to have a jl_yield() function in the Julia API to make this sort of thing easier. Maybe file an issue in Julia.

[cbecker]

Yes, would be great. The issue is that yield() is in julia code now, and doing jl_eval_string("yield()"); crashes Julia when the function returns.

About my original question, I understand if the contents I printed appear when the function returns, but in the case of using ipython console --profile julia I don't get any of the output at all.

[stevengj]

@minrk, does the ipython console not support stream messages?

[minrk]

It does - all Python print statements are stream messages. I can print with println("1") in ipython console --profile julia.