repo.walk in thread hangs the main thread

When calling repo.walk in a new thread, it blocks the main thread until it finished!!!

See the example code below, when run with a huge repo (qt5, chromium e.g.), the main thread won't print any message until the repo.walk ended. (Use iter also the same)

It seems that repo.diff also have the problem.

from pygit2 import Repository, GIT_SORT_TOPOLOGICAL
from threading import Thread

import sys
import time


def thread_func(repo_dir):
    repo = Repository(repo_dir)

    print(">>>>>>>> begin diff")
    commits = list(repo.walk(repo.head.target, GIT_SORT_TOPOLOGICAL))
    #for commit in repo.walk(repo.head.target, GIT_SORT_TOPOLOGICAL):
    #    continue
    print(">>>>>>>> end diff")


def test(repo_dir):
    t = Thread(target=thread_func, args=[repo_dir])
    t.start()

    while t.is_alive():
        print("main thread...")
        time.sleep(0.01)


if __name__ == "__main__":
    if len(sys.argv) != 2:
        print(">>>>>>>> Invalid argument")
        sys.exit(-1)

    test(sys.argv[1])

Start with the provided Python reproducer and inspect the implementations of repo.walk, its iterator, and repo.diff for threading behavior. Verify whether the main thread remains responsive while the worker processes a large repository, then add regression coverage demonstrating the expected behavior.