在std :: thread中用SOIL加载OpenGL纹理会引发“整数除以零”

Question

I can load a texture just fine in SOIL/OpenGL normally. No errors, everything works fine:

// this is inside my texture loading code in my texture class
// that i normally use for loading textures
image = SOIL_load_OGL_texture
    (
    file,
    SOIL_LOAD_AUTO,
    SOIL_CREATE_NEW_ID,
    NULL
    );

However, using that same code and calling it from an std::thread, at the line image = SOIL_load_OGL_texture I get unhandled exception Integer Division by Zero :

void loadMe() {
    Texture* abc = new Texture("res/img/office.png");
}

void loadStuff() {
    Texture* loading = new Texture("res/img/head.png"); // < always works

    loadMe() // < always works
    std::thread textures(loadMe); // < always "integer division by zero"

Here's some relevant code from my Texture class:

// inside the class
private:
    GLint w, h;
    GLuint image;

// loading the texture (called by constructor if filename is given)
void Texture::loadImage(const char* file)
{

    image = SOIL_load_OGL_texture
        (
        file,
        SOIL_LOAD_AUTO,
        SOIL_CREATE_NEW_ID,
        NULL
        );

    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, image);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH, &w);
    glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_HEIGHT, &h);
    glBindTexture(GL_TEXTURE_2D, 0);

    if (image <= 0)
        std::cout << file << " failed to load!\n";
    else
        std::cout << file << " loaded.\n";

    glDisable(GL_TEXTURE_2D);
}

It raises the exception exactly at image = SOIL_load_OGL_texture , and when I go into the debugger, I see things like w = -816294792 and w = -816294792 , but I guess that just means it hasn't been set yet, as it also shows that in the debugger for loading the other textures.

Also, the SOIL_load_OGL_texture part of the code works fine by itself, outside of the Texture class, even in a std::thread.

Any idea what's going on here?

Answer 1

This is how you do it. Note that, as others have mentioned in the comments, a context needs to be maintained current for every thread that uses GL. What this means is practically there cannot be a GL API call made in multiple threads without making one thread the owner of the GL context. Hence if the intention is to separate the Image loading overhead it is recommended to load the image file into a buffer using a library in a separate thread, then use that buffer to glTexImage2D in the main thread. Till the image is loaded, a dummy texture can be displayed.

I tried checking what platform you are on (see comment above), since I did not see a response, I am assuming Linux for below.

/* Regular GL context creation foo */
/* Regular attribute, uniform, shader creation foo */
/* Create a thread that does loading with SOIL in function SOIL_loader */
std::thread textureloader(SOIL_loader);
/* Wait for loader thread to finish, 
thus defeating the purpose of a thread. Ideally, 
only the image file read/decode should happen in separate thread */
textureloader.join();
/* Make the GL context current back again in the main thread 
for other actions */
glfwMakeContextCurrent((GLFWwindow*)window);
/* Some other foo */

======

And this is the loader thread function:

void SOIL_loader()
{
   glfwMakeContextCurrent((GLFWwindow*)window);
    SOIL_load_OGL_texture
        (
        "./img_test.png",
        SOIL_LOAD_AUTO,
        SOIL_CREATE_NEW_ID /* or passed ID */,
        NULL
        );
   GL_CHECK(SOIL);
}

Tested on Ubuntu 14.04, Mesa, and glfw3.