test_weakref.py

# Copyright (c) 2025, NVIDIA CORPORATION.
# SPDX-License-Identifier: BSD-3-Clause
import multiprocessing
import unittest
from dataclasses import dataclass

from megatron.energon.fork_hook import (
    DataclassForkMixin,
    ForkMixin,
    WeakCallbacks,
    after_in_child_fork_hook,
    after_in_parent_fork_hook,
    before_fork_hook,
)


class TestWeakref(unittest.TestCase):
    def test_weakcallbacks(self):
        # Just test the internal WeakCallbacks class.
        a_called = 0
        fn_called = 0

        class A:
            def method(self):
                nonlocal a_called
                a_called += 1

        def fn():
            nonlocal fn_called
            fn_called += 1

        a = A()

        registry = WeakCallbacks()

        registry.add_hook(a.method)
        registry.add_hook(fn)
        registry.add_hook(a.method)

        registry.run()

        assert a_called == 1, a_called
        assert fn_called == 1, fn_called

        assert len(registry._hooks) == 2, len(registry._hooks)

        del a

        assert len(registry._hooks) == 1, len(registry._hooks)

        registry.run()

        assert a_called == 1, a_called
        assert fn_called == 2, fn_called

        del fn

        assert len(registry._hooks) == 0, len(registry._hooks)

        registry.run()

        assert a_called == 1, a_called
        assert fn_called == 2, fn_called

        assert len(registry._hooks) == 0, len(registry._hooks)

    def test_fork_weakref(self):
        # Verify that the fork hooks are called correctly, and that gc works correctly.

        _a_before_fork_called = 0
        _a_after_in_child_fork_called = 0
        _a_after_in_parent_fork_called = 0

        class A(ForkMixin):
            def __before_fork__(self):
                nonlocal _a_before_fork_called
                _a_before_fork_called += 1

            def __after_in_child_fork__(self):
                nonlocal _a_after_in_child_fork_called
                _a_after_in_child_fork_called += 1

            def __after_in_parent_fork__(self):
                nonlocal _a_after_in_parent_fork_called
                _a_after_in_parent_fork_called += 1

        _b_before_fork_called = 0
        _b_after_in_child_fork_called = 0
        _b_after_in_parent_fork_called = 0

        @dataclass
        class B(DataclassForkMixin):
            def __before_fork__(self):
                nonlocal _b_before_fork_called
                _b_before_fork_called += 1

            def __after_in_child_fork__(self):
                nonlocal _b_after_in_child_fork_called
                _b_after_in_child_fork_called += 1

            def __after_in_parent_fork__(self):
                nonlocal _b_after_in_parent_fork_called
                _b_after_in_parent_fork_called += 1

        a = A()
        b = B()

        _before_fork_called = 0
        _after_in_child_fork_called = 0
        _after_in_parent_fork_called = 0

        def before_fork():
            nonlocal _before_fork_called
            _before_fork_called += 1

        def after_in_child_fork():
            nonlocal _after_in_child_fork_called
            _after_in_child_fork_called += 1

        def after_in_parent_fork():
            nonlocal _after_in_parent_fork_called
            _after_in_parent_fork_called += 1

        before_fork_hook(before_fork)
        after_in_child_fork_hook(after_in_child_fork)
        after_in_parent_fork_hook(after_in_parent_fork)

        multiprocessing.set_start_method("fork", force=True)

        def process_verify_fork_hooks_1():
            # Verify in the process that the fork hooks were called
            assert _before_fork_called == 1, _before_fork_called
            assert _after_in_child_fork_called == 1, _after_in_child_fork_called
            # This was not called in the child process
            assert _after_in_parent_fork_called == 0, _after_in_parent_fork_called

            assert _a_before_fork_called == 1, _a_before_fork_called
            assert _a_after_in_child_fork_called == 1, _a_after_in_child_fork_called
            assert _a_after_in_parent_fork_called == 0, _a_after_in_parent_fork_called

            assert _b_before_fork_called == 1, _b_before_fork_called
            assert _b_after_in_child_fork_called == 1, _b_after_in_child_fork_called
            assert _b_after_in_parent_fork_called == 0, _b_after_in_parent_fork_called

        p1 = multiprocessing.Process(target=process_verify_fork_hooks_1)
        p1.start()
        p1.join()
        assert p1.exitcode == 0, p1.exitcode

        assert _before_fork_called == 1, _before_fork_called
        assert _after_in_child_fork_called == 0, _after_in_child_fork_called
        assert _after_in_parent_fork_called == 1, _after_in_parent_fork_called

        assert _a_before_fork_called == 1, _a_before_fork_called
        assert _a_after_in_child_fork_called == 0, _a_after_in_child_fork_called
        assert _a_after_in_parent_fork_called == 1, _a_after_in_parent_fork_called

        assert _b_before_fork_called == 1, _b_before_fork_called
        assert _b_after_in_child_fork_called == 0, _b_after_in_child_fork_called
        assert _b_after_in_parent_fork_called == 1, _b_after_in_parent_fork_called

        _a_before_fork_called = 0
        _a_after_in_child_fork_called = 0
        _a_after_in_parent_fork_called = 0

        _b_before_fork_called = 0
        _b_after_in_child_fork_called = 0
        _b_after_in_parent_fork_called = 0

        _before_fork_called = 0
        _after_in_child_fork_called = 0
        _after_in_parent_fork_called = 0

        del a
        del b
        del before_fork
        del after_in_child_fork
        del after_in_parent_fork

        def process_verify_fork_hooks_2():
            assert _before_fork_called == 0, _before_fork_called
            assert _after_in_child_fork_called == 0, _after_in_child_fork_called
            assert _after_in_parent_fork_called == 0, _after_in_parent_fork_called

            assert _a_before_fork_called == 0, _a_before_fork_called
            assert _a_after_in_child_fork_called == 0, _a_after_in_child_fork_called
            assert _a_after_in_parent_fork_called == 0, _a_after_in_parent_fork_called

            assert _b_before_fork_called == 0, _b_before_fork_called
            assert _b_after_in_child_fork_called == 0, _b_after_in_child_fork_called
            assert _b_after_in_parent_fork_called == 0, _b_after_in_parent_fork_called

        p2 = multiprocessing.Process(target=process_verify_fork_hooks_2)
        p2.start()
        p2.join()
        assert p2.exitcode == 0, p2.exitcode

        assert _before_fork_called == 0, _before_fork_called
        assert _after_in_child_fork_called == 0, _after_in_child_fork_called
        assert _after_in_parent_fork_called == 0, _after_in_parent_fork_called

        assert _a_before_fork_called == 0, _a_before_fork_called
        assert _a_after_in_child_fork_called == 0, _a_after_in_child_fork_called
        assert _a_after_in_parent_fork_called == 0, _a_after_in_parent_fork_called

        assert _b_before_fork_called == 0, _b_before_fork_called
        assert _b_after_in_child_fork_called == 0, _b_after_in_child_fork_called
        assert _b_after_in_parent_fork_called == 0, _b_after_in_parent_fork_called