There are two contexts, a worker context and a render context. During setup, the worker thread creates and sets up the shader and VBO. The render thread then uses the the VBO to create a VAO and draw it. I get nothing on screen (or old vertices, see below).
If I allow the render thread to also create the VBO before it creates the VAO, everything works, I see a triangle, rendered with the shader program created in the worker thread.
The really weird part is after it works, if I switch it back to VBO creation in the worker thread, I still see the triangle but if I change the geometry of the triangle it is not updated until I switch it back to VBO creation in the render thread.
This is incredibly odd. Both ways the render context is using a shader created in the worker context, but I can't seem to share the VBO, yet when the worker context creates the VBO the vertices are not updated and the triangle from the previous program run draws.
I'm on Ubuntu 16. This was happening with glew, now glbinding, and my own compiled latest glfw3 and the Ubuntu package as well.
In summary, VBO creation and drawing works from the main thread with a shader created from the worker thread. If I try to create a VBO with the worker thread (same function) I seem to get access to a new buffer that happens to have old data when it is used in the render thread...
The thread that uses the object merely has to bind it. The thread the updates the object (worker thread in this case) must use
glFlush();
to make sure the update is processed and available to the other context.