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gh-116622: Mock the passage of time in Android logcat rate limit tests #124015

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Merged
merged 2 commits into from
Sep 13, 2024
Merged

gh-116622: Mock the passage of time in Android logcat rate limit tests #124015

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e4cb124
Mock the passage of time in Android logcat rate limit tests
mhsmith Sep 12, 2024
b2bf343
Merge branch 'main' into android-rate-limit
freakboy3742 Sep 13, 2024
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5 changes: 4 additions & 1 deletion Lib/_android_support.py
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Original file line number Diff line number Diff line change
Expand Up @@ -165,7 +165,10 @@ def write(self, prio, tag, message):
now = time()
self._bucket_level += (
(now - self._prev_write_time) * MAX_BYTES_PER_SECOND)
self._bucket_level = min(self._bucket_level, BUCKET_SIZE)

# If the bucket level is still below zero, the clock must have gone
# backwards, so reset it to zero and continue.
self._bucket_level = max(0, min(self._bucket_level, BUCKET_SIZE))
self._prev_write_time = now

self._bucket_level -= PER_MESSAGE_OVERHEAD + len(tag) + len(message)
Expand Down
32 changes: 26 additions & 6 deletions Lib/test/test_android.py
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@
from contextlib import ExitStack, contextmanager
from threading import Thread
from test.support import LOOPBACK_TIMEOUT
from time import sleep, time
from time import time
from unittest.mock import patch


Expand Down Expand Up @@ -42,7 +42,8 @@ def logcat_thread():
for line in self.logcat_process.stdout:
self.logcat_queue.put(line.rstrip("\n"))
self.logcat_process.stdout.close()
Thread(target=logcat_thread).start()
self.logcat_thread = Thread(target=logcat_thread)
self.logcat_thread.start()

from ctypes import CDLL, c_char_p, c_int
android_log_write = getattr(CDLL("liblog.so"), "__android_log_write")
Expand Down Expand Up @@ -78,6 +79,7 @@ def assert_log(self, level, tag, expected, *, skip=False, timeout=0.5):
def tearDown(self):
self.logcat_process.terminate()
self.logcat_process.wait(LOOPBACK_TIMEOUT)
self.logcat_thread.join(LOOPBACK_TIMEOUT)
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This fixes an unrelated warning I saw while running the tests repeatedly with -F:

Warning -- threading._dangling was modified by test_android
Warning --   Before: {<weakref at 0x7c15b68e00; to 'threading._MainThread' at 0x7c18f5fcb0>}
Warning --   After:  {<weakref at 0x7c186e3ce0; to 'threading._MainThread' at 0x7c18f5fcb0>, <weakref at 0x7c1870ef20; to 'threading.Thread' at 0x7c183faa50>}


@contextmanager
def unbuffered(self, stream):
Expand Down Expand Up @@ -369,6 +371,8 @@ def write(b, lines=None, *, write_len=None):
):
stream.write(obj)


class TestAndroidRateLimit(unittest.TestCase):
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This test doesn't read its own output, so it doesn't need the @skipIf or the setUp from the other class.

def test_rate_limit(self):
# https://cs.android.com/android/platform/superproject/+/android-14.0.0_r1:system/logging/liblog/include/log/log_read.h;l=39
PER_MESSAGE_OVERHEAD = 28
Expand All @@ -387,6 +391,19 @@ def test_rate_limit(self):
1024 - PER_MESSAGE_OVERHEAD - len(tag) - len(message.format(0))
) + "\n"

# To avoid depending on the performance of the test device, we mock the
# passage of time.
mock_now = time()

def mock_time():
# Avoid division by zero by simulating a small delay.
mock_sleep(0.0001)
return mock_now

def mock_sleep(duration):
nonlocal mock_now
mock_now += duration

# See _android_support.py. The default values of these parameters work
# well across a wide range of devices, but we'll use smaller values to
# ensure a quick and reliable test that doesn't flood the log too much.
Expand All @@ -395,21 +412,24 @@ def test_rate_limit(self):
with (
patch("_android_support.MAX_BYTES_PER_SECOND", MAX_KB_PER_SECOND * 1024),
patch("_android_support.BUCKET_SIZE", BUCKET_KB * 1024),
patch("_android_support.sleep", mock_sleep),
patch("_android_support.time", mock_time),
):
# Make sure the token bucket is full.
sleep(BUCKET_KB / MAX_KB_PER_SECOND)
stream.write("Initial message to reset _prev_write_time")
mock_sleep(BUCKET_KB / MAX_KB_PER_SECOND)
line_num = 0

# Write BUCKET_KB messages, and return the rate at which they were
# accepted in KB per second.
def write_bucketful():
nonlocal line_num
start = time()
start = mock_time()
max_line_num = line_num + BUCKET_KB
while line_num < max_line_num:
stream.write(message.format(line_num))
line_num += 1
return BUCKET_KB / (time() - start)
return BUCKET_KB / (mock_time() - start)

# The first bucketful should be written with minimal delay. The
# factor of 2 here is not arbitrary: it verifies that the system can
Expand All @@ -427,5 +447,5 @@ def write_bucketful():
)

# Once the token bucket refills, we should go back to full speed.
sleep(BUCKET_KB / MAX_KB_PER_SECOND)
mock_sleep(BUCKET_KB / MAX_KB_PER_SECOND)
self.assertGreater(write_bucketful(), MAX_KB_PER_SECOND * 2)
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