Re: [PyOpenGL-Users] glReadPixels not working in thread

[Ian M. <ia...@ge...>]

​It's not entirely clear to me your setup. It looks like you're trying to
use a subprocess? A few things:

- Threads in Python add parallelism, but not performance, due to the global
interpreter lock. They may even be pure software threads.
- OpenGL contexts are not threadsafe. It is usually considered an error to
use OpenGL from multiple threads, although in-principle it can be done if
the parallel executions correspond to a serial execution, with no overlaps
(through, e.g., tons of mutexes).
- Subprocesses definitely will suffer at least that problem. IDR exactly,
but it may be an error to attempt to share a GL context across
subprocesses, regardless of any synchronization.

Recommendation: keep all GL calls in one thread, and don't use threads in
Python anyway unless you need asynchronous operations. If profiling shows
that OpenGL *command overhead* really is the bottleneck *and* this is worth
investing effort fixing, move to C++. If you still don't have enough
performance, move from OpenGL to Vulkan (which unlike GL will allow you to
build and issue command lists in parallel).

Ian