OpenJPH bindings

Requirements

These bindings link against OpenJPH and require a version containing PR #312 ("Removes direct access to COC segment marker"). That change was merged after the 0.30.1 release and, at the time of writing, is only available on OpenJPH main (unreleased). Building against OpenJPH 0.30.1 or earlier is not supported.

Free-threaded Python

ojph supports free-threaded (PEP 703) CPython 3.13t/3.14t: the extension declares that it does not need the GIL, so importing it leaves the GIL disabled. Wheels are published for cp314t, and the test suite runs on a free-threaded interpreter in CI.

The decode and encode hot paths already release the GIL, so a thread pool scales across cores on a free-threaded interpreter:

from concurrent.futures import ThreadPoolExecutor
from ojph.ojph_bindings import read_j2c_into

with ThreadPoolExecutor() as pool:
    pool.map(lambda t: read_j2c_into(t.data, t.out, t.level), tiles)

As with a file object, a single Codestream, infile or outfile object must not be shared between threads without external synchronisation. Give each thread its own; a compressed buffer that is only read can safely be shared.