test_response_cache.py

# Copyright 2021 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from unittest.mock import Mock

from parameterized import parameterized

from twisted.internet import defer

from synapse.util.caches.response_cache import ResponseCache, ResponseCacheContext

from tests.server import get_clock
from tests.unittest import TestCase


class ResponseCacheTestCase(TestCase):
    """
    A TestCase class for ResponseCache.

    The test-case function naming has some logic to it in it's parts, here's some notes about it:
        wait: Denotes tests that have an element of "waiting" before its wrapped result becomes available
              (Generally these just use .delayed_return instead of .instant_return in it's wrapped call.)
        expire: Denotes tests that test expiry after assured existence.
                (These have cache with a short timeout_ms=, shorter than will be tested through advancing the clock)
    """

    def setUp(self):
        self.reactor, self.clock = get_clock()

    def with_cache(self, name: str, ms: int = 0) -> ResponseCache:
        return ResponseCache(self.clock, name, timeout_ms=ms)

    @staticmethod
    async def instant_return(o: str) -> str:
        return o

    async def delayed_return(self, o: str) -> str:
        await self.clock.sleep(1)
        return o

    def test_cache_hit(self):
        cache = self.with_cache("keeping_cache", ms=9001)

        expected_result = "howdy"

        wrap_d = defer.ensureDeferred(
            cache.wrap(0, self.instant_return, expected_result)
        )

        self.assertEqual(
            expected_result,
            self.successResultOf(wrap_d),
            "initial wrap result should be the same",
        )

        # a second call should return the result without a call to the wrapped function
        unexpected = Mock(spec=())
        wrap2_d = defer.ensureDeferred(cache.wrap(0, unexpected))
        unexpected.assert_not_called()
        self.assertEqual(
            expected_result,
            self.successResultOf(wrap2_d),
            "cache should still have the result",
        )

    def test_cache_miss(self):
        cache = self.with_cache("trashing_cache", ms=0)

        expected_result = "howdy"

        wrap_d = defer.ensureDeferred(
            cache.wrap(0, self.instant_return, expected_result)
        )

        self.assertEqual(
            expected_result,
            self.successResultOf(wrap_d),
            "initial wrap result should be the same",
        )
        self.assertCountEqual([], cache.keys(), "cache should not have the result now")

    def test_cache_expire(self):
        cache = self.with_cache("short_cache", ms=1000)

        expected_result = "howdy"

        wrap_d = defer.ensureDeferred(
            cache.wrap(0, self.instant_return, expected_result)
        )

        self.assertEqual(expected_result, self.successResultOf(wrap_d))

        # a second call should return the result without a call to the wrapped function
        unexpected = Mock(spec=())
        wrap2_d = defer.ensureDeferred(cache.wrap(0, unexpected))
        unexpected.assert_not_called()
        self.assertEqual(
            expected_result,
            self.successResultOf(wrap2_d),
            "cache should still have the result",
        )

        # cache eviction timer is handled
        self.reactor.pump((2,))
        self.assertCountEqual([], cache.keys(), "cache should not have the result now")

    def test_cache_wait_hit(self):
        cache = self.with_cache("neutral_cache")

        expected_result = "howdy"

        wrap_d = defer.ensureDeferred(
            cache.wrap(0, self.delayed_return, expected_result)
        )

        self.assertNoResult(wrap_d)

        # function wakes up, returns result
        self.reactor.pump((2,))

        self.assertEqual(expected_result, self.successResultOf(wrap_d))

    def test_cache_wait_expire(self):
        cache = self.with_cache("medium_cache", ms=3000)

        expected_result = "howdy"

        wrap_d = defer.ensureDeferred(
            cache.wrap(0, self.delayed_return, expected_result)
        )
        self.assertNoResult(wrap_d)

        # stop at 1 second to callback cache eviction callLater at that time, then another to set time at 2
        self.reactor.pump((1, 1))

        self.assertEqual(expected_result, self.successResultOf(wrap_d))

        # a second call should immediately return the result without a call to the
        # wrapped function
        unexpected = Mock(spec=())
        wrap2_d = defer.ensureDeferred(cache.wrap(0, unexpected))
        unexpected.assert_not_called()
        self.assertEqual(
            expected_result,
            self.successResultOf(wrap2_d),
            "cache should still have the result",
        )

        # (1 + 1 + 2) > 3.0, cache eviction timer is handled
        self.reactor.pump((2,))
        self.assertCountEqual([], cache.keys(), "cache should not have the result now")

    @parameterized.expand([(True,), (False,)])
    def test_cache_context_nocache(self, should_cache: bool):
        """If the callback clears the should_cache bit, the result should not be cached"""
        cache = self.with_cache("medium_cache", ms=3000)

        expected_result = "howdy"

        call_count = 0

        async def non_caching(o: str, cache_context: ResponseCacheContext[int]):
            nonlocal call_count
            call_count += 1
            await self.clock.sleep(1)
            cache_context.should_cache = should_cache
            return o

        wrap_d = defer.ensureDeferred(
            cache.wrap(0, non_caching, expected_result, cache_context=True)
        )
        # there should be no result to start with
        self.assertNoResult(wrap_d)

        # a second call should also return a pending deferred
        wrap2_d = defer.ensureDeferred(
            cache.wrap(0, non_caching, expected_result, cache_context=True)
        )
        self.assertNoResult(wrap2_d)

        # and there should have been exactly one call
        self.assertEqual(call_count, 1)

        # let the call complete
        self.reactor.advance(1)

        # both results should have completed
        self.assertEqual(expected_result, self.successResultOf(wrap_d))
        self.assertEqual(expected_result, self.successResultOf(wrap2_d))

        if should_cache:
            unexpected = Mock(spec=())
            wrap3_d = defer.ensureDeferred(cache.wrap(0, unexpected))
            unexpected.assert_not_called()
            self.assertEqual(
                expected_result,
                self.successResultOf(wrap3_d),
                "cache should still have the result",
            )

        else:
            self.assertCountEqual(
                [], cache.keys(), "cache should not have the result now"
            )