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"""A pytest plugin to trace resource leaks.
Usage
-----
This plugin is enabled from the command line with -L / --leaks.
See `pytest --help` for further configuration settings.
You may mark individual tests as known to be leaking with the fixture
@pytest.mark.leaking(check1, check2, ...)
Where the valid checks are 'fds', 'memory', 'threads', 'processes', 'tracemalloc'.
e.g.
@pytest.mark.leaking("threads")
If you do, the specified checks won't report errors.
Known issues
------------
- Tests that contain imports will be flagged as leaking RAM (memory and tracemallock
checks) if it's the first time in the test suite that the import happens; e.g.
def test1():
pytest.importorskip("numpy")
Same issue happens with tests that populate global caches (e.g. linecache, re).
A previous version of this plugin had an option to silently retry a test once after a
failure; that version is no longer working as of the latest pytest. Reinstating the
flag would solve this issue. See pytest_rerunfailures code for inspiration.
- The @gen_cluster fixture leaks 2 fds on the first test decorated with it within a test
suite; This issue would also be fixed by rerunning failing tests.
- The @pytest.mark.flaky decorator (pytest_rerunfailures) completely disables this
plugin for the decorated tests.
- You cannot expect the process memory to go down immediately and deterministically as
soon as you garbage collect Python objects. This makes the 'memory' check very
unreliable. On Linux, this can be improved by reducing the MALLOC_TRIM glibc setting
(see distributed.yaml).
"""
from __future__ import annotations
import gc
import os
import sys
import threading
import tracemalloc
from collections import defaultdict
from time import sleep
from typing import Any, ClassVar
import psutil
import pytest
from distributed.metrics import time
def pytest_addoption(parser):
group = parser.getgroup("resource leaks")
known_checkers = ", ".join(sorted("'%s'" % s for s in all_checkers))
group.addoption(
"-L",
"--leaks",
help="List of resources to monitor for leaks before and after each test. "
"Can be 'all' or a comma-separated list of resource names "
f"(possible values: {known_checkers}).",
)
group.addoption(
"--leaks-timeout",
type=float,
default=0.5,
help="Wait at most these many seconds before marking a test as leaking "
"(default: %(default)s)",
)
group.addoption(
"--leaks-fail",
action="store_true",
help="Mark leaked tests as failed",
)
def pytest_configure(config: pytest.Config) -> None:
leaks = config.getvalue("leaks")
if not leaks:
return
if leaks == "all":
leaks = sorted(c for c in all_checkers if c != "demo")
else:
leaks = leaks.split(",")
unknown = sorted(set(leaks) - set(all_checkers))
if unknown:
raise ValueError(f"unknown resources: {unknown!r}")
checkers = [all_checkers[leak]() for leak in leaks]
checker = LeakChecker(
checkers=checkers,
grace_delay=config.getvalue("leaks_timeout"),
mark_failed=config.getvalue("leaks_fail"),
)
config.pluginmanager.register(checker, "leaks_checker")
all_checkers: dict[str, type[ResourceChecker]] = {}
class ResourceChecker:
name: ClassVar[str]
def __init_subclass__(cls, name: str):
assert name not in all_checkers
cls.name = name
all_checkers[name] = cls
def on_start_test(self) -> None:
pass
def on_stop_test(self) -> None:
pass
def on_retry(self) -> None:
pass
def measure(self) -> Any:
raise NotImplementedError
def has_leak(self, before: Any, after: Any) -> bool:
raise NotImplementedError
def format(self, before: Any, after: Any) -> str:
raise NotImplementedError
class DemoChecker(ResourceChecker, name="demo"):
"""Checker that always leaks. Used to test the core LeakChecker functionality."""
i: int
def __init__(self):
self.i = 0
def measure(self) -> int:
self.i += 1
return self.i
def has_leak(self, before: int, after: int) -> bool:
return after > before
def format(self, before: int, after: int) -> str:
return f"counter increased from {before} to {after}"
class FDChecker(ResourceChecker, name="fds"):
def measure(self) -> int:
# Note: WINDOWS constant doesn't work with `mypy --platform win32`
if sys.platform == "win32":
# Don't use num_handles(); you'll get tens of thousands of reported leaks
return 0
else:
return psutil.Process().num_fds()
def has_leak(self, before: int, after: int) -> bool:
return after > before
def format(self, before: int, after: int) -> str:
return f"leaked {after - before} file descriptor(s) ({before}->{after})"
class RSSMemoryChecker(ResourceChecker, name="memory"):
LEAK_THRESHOLD = 10 * 2**20
def measure(self) -> int:
return psutil.Process().memory_info().rss
def has_leak(self, before: int, after: int) -> bool:
return after > before + self.LEAK_THRESHOLD
def format(self, before: int, after: int) -> str:
return f"leaked {(after - before) / 2**20:.1f} MiB of RSS memory"
class ActiveThreadsChecker(ResourceChecker, name="threads"):
def measure(self) -> set[threading.Thread]:
return set(threading.enumerate())
def has_leak(
self, before: set[threading.Thread], after: set[threading.Thread]
) -> bool:
return not after <= before
def format(
self, before: set[threading.Thread], after: set[threading.Thread]
) -> str:
leaked = after - before
assert leaked
return f"leaked {len(leaked)} Python thread(s): {sorted(leaked, key=str)}"
class ChildProcess:
"""Child process info
We use pid and creation time as keys to disambiguate between processes (and protect
against pid reuse); other properties such as cmdline may change for a given process
"""
pid: int
name: str
cmdline: list[str]
create_time: float
def __init__(self, p: psutil.Process):
self.pid = p.pid
self.name = p.name()
self.cmdline = p.cmdline()
self.create_time = p.create_time()
def __hash__(self) -> int:
return self.pid
def __eq__(self, other: object) -> bool:
return (
isinstance(other, ChildProcess)
and self.pid == other.pid
and self.create_time == other.create_time
)
def __lt__(self, other: object) -> bool:
if not isinstance(other, ChildProcess):
raise TypeError(other)
return self.pid < other.pid
class ChildProcessesChecker(ResourceChecker, name="processes"):
def measure(self) -> set[ChildProcess]:
children = set()
p = psutil.Process()
for c in p.children(recursive=True):
try:
with c.oneshot():
if (
c.ppid() == p.pid
and os.path.samefile(c.exe(), sys.executable)
and any(
# Skip multiprocessing resource tracker
a.startswith(
"from multiprocessing.resource_tracker import main"
)
# Skip forkserver process; the forkserver's children
# however will be recorded normally
or a.startswith(
"from multiprocessing.forkserver import main"
)
for a in c.cmdline()
)
):
continue
children.add(ChildProcess(c))
except psutil.NoSuchProcess:
pass
return children
def has_leak(self, before: set[ChildProcess], after: set[ChildProcess]) -> bool:
return not after <= before
def format(self, before: set[ChildProcess], after: set[ChildProcess]) -> str:
leaked = sorted(after - before)
assert leaked
return f"leaked {len(leaked)} processes:\n" + "\n".join(
f" - pid={p.pid}, name={p.name!r}, cmdline={p.cmdline!r}" for p in leaked
)
class TracemallocMemoryChecker(ResourceChecker, name="tracemalloc"):
# Report a leak if the traced memory increased by at least this many bytes
LEAK_THRESHOLD = 2**20
# Report at most this many leaks
NDIFF = 5
# Report less than NDIFF leaks if they amount to less than this many bytes
MIN_SIZE_DIFF = 200 * 1024
def on_start_test(self) -> None:
tracemalloc.start(1)
def on_stop_test(self) -> None:
tracemalloc.stop()
def measure(self) -> tuple[int, tracemalloc.Snapshot]:
current, _ = tracemalloc.get_traced_memory()
snap = tracemalloc.take_snapshot()
return current, snap
def has_leak(
self,
before: tuple[int, tracemalloc.Snapshot],
after: tuple[int, tracemalloc.Snapshot],
) -> bool:
return after[0] > before[0] + self.LEAK_THRESHOLD
def format(
self,
before: tuple[int, tracemalloc.Snapshot],
after: tuple[int, tracemalloc.Snapshot],
) -> str:
bytes_before, snap_before = before
bytes_after, snap_after = after
diff = snap_after.compare_to(snap_before, "traceback")
lines = [
f"leaked {(bytes_after - bytes_before) / 2 ** 20:.1f} MiB "
"of traced Python memory"
]
for stat in diff[: self.NDIFF]:
size_diff = stat.size_diff or stat.size
if size_diff < self.MIN_SIZE_DIFF:
break
count = stat.count_diff or stat.count
lines += [f" - leaked {size_diff / 2**20:.1f} MiB in {count} calls at:"]
lines += [" " + line for line in stat.traceback.format()]
return "\n".join(lines)
class LeakChecker:
checkers: list[ResourceChecker]
grace_delay: float
mark_failed: bool
# {nodeid: {checkers}}
skip_checkers: dict[str, set[ResourceChecker]]
# {nodeid: {checker: [(before, after)]}}
counters: dict[str, dict[ResourceChecker, list[tuple[Any, Any]]]]
# {nodeid: [(checker, before, after)]}
leaks: dict[str, list[tuple[ResourceChecker, Any, Any]]]
# {nodeid: {outcomes}}
outcomes: defaultdict[str, set[str]]
def __init__(
self,
checkers: list[ResourceChecker],
grace_delay: float,
mark_failed: bool,
):
self.checkers = checkers
self.grace_delay = grace_delay
self.mark_failed = mark_failed
self.skip_checkers = {}
self.counters = {}
self.leaks = {}
self.outcomes = defaultdict(set)
def cleanup(self) -> None:
gc.collect()
def checks_for_item(self, nodeid: str) -> list[ResourceChecker]:
return [c for c in self.checkers if c not in self.skip_checkers.get(nodeid, ())]
def measure(self, nodeid: str) -> list[tuple[ResourceChecker, Any]]:
# Return items in order
return [(c, c.measure()) for c in self.checks_for_item(nodeid)]
def measure_before_test(self, nodeid: str) -> None:
for checker in self.checks_for_item(nodeid):
checker.on_start_test()
for checker, before in self.measure(nodeid):
assert before is not None
self.counters[nodeid][checker].append((before, None))
def measure_after_test(self, nodeid: str) -> None:
outcomes = self.outcomes[nodeid]
# pytest_rerunfailures (@pytest.mark.flaky) breaks this plugin and causes
# outcomes to be empty.
if "passed" not in outcomes:
# Test failed or skipped
return
def run_measurements() -> list[tuple[ResourceChecker, Any, Any]]:
leaks = []
for checker, after in self.measure(nodeid):
c = self.counters[nodeid][checker]
before, _ = c[-1]
c[-1] = (before, after)
if checker.has_leak(before, after):
leaks.append((checker, before, after))
return leaks
t1 = time()
deadline = t1 + self.grace_delay
leaks = run_measurements()
if leaks:
self.cleanup()
for c, _, _ in leaks:
c.on_retry()
leaks = run_measurements()
while leaks and time() < deadline:
sleep(0.1)
self.cleanup()
for c, _, _ in leaks:
c.on_retry()
leaks = run_measurements()
if leaks:
self.leaks[nodeid] = leaks
else:
self.leaks.pop(nodeid, None)
for checker in self.checks_for_item(nodeid):
checker.on_stop_test()
# Note on hook execution order:
# pytest_runtest_protocol
# pytest_runtest_setup
# pytest_report_teststatus
# pytest_runtest_call
# pytest_report_teststatus
# pytest_runtest_teardown
# pytest_report_teststatus
# See also https://github.com/abalkin/pytest-leaks/blob/master/pytest_leaks.py
@pytest.hookimpl(hookwrapper=True)
def pytest_runtest_protocol(self, item, nextitem):
if not self.checkers:
return
nodeid = item.nodeid
assert nodeid not in self.counters
self.counters[nodeid] = {c: [] for c in self.checkers}
leaking_mark = item.get_closest_marker("leaking")
if leaking_mark:
unknown = sorted(set(leaking_mark.args) - set(all_checkers))
if unknown:
raise ValueError(
f"pytest.mark.leaking: unknown resources {unknown}; "
f"must be one of {list(all_checkers)}"
)
classes = tuple(all_checkers[a] for a in leaking_mark.args)
self.skip_checkers[nodeid] = {
c for c in self.checkers if isinstance(c, classes)
}
yield
@pytest.hookimpl(hookwrapper=True)
def pytest_runtest_setup(self, item):
self.measure_before_test(item.nodeid)
yield
@pytest.hookimpl(hookwrapper=True, trylast=True)
def pytest_runtest_teardown(self, item):
yield
self.measure_after_test(item.nodeid)
leaks = self.leaks.get(item.nodeid)
if leaks and self.mark_failed:
# Trigger fail here to allow stopping with `-x`
pytest.fail()
@pytest.hookimpl(hookwrapper=True, trylast=True)
def pytest_report_teststatus(self, report):
nodeid = report.nodeid
self.outcomes[nodeid].add(report.outcome)
outcome = yield
if report.when == "teardown":
leaks = self.leaks.get(report.nodeid)
if leaks:
if self.mark_failed:
outcome.force_result(("failed", "L", "LEAKED"))
report.outcome = "failed"
report.longrepr = "\n".join(
[
f"{nodeid} leaking {checker.name}: "
f"{checker.format(before, after)}"
for checker, before, after in leaks
]
)
else:
outcome.force_result(("leaked", "L", "LEAKED"))
@pytest.hookimpl
def pytest_terminal_summary(self, terminalreporter, exitstatus):
tr = terminalreporter
leaked = tr.getreports("leaked")
if leaked:
# If mark_failed is False, leaks are output as a separate
# results section
tr.write_sep("=", "RESOURCE LEAKS")
for rep in leaked:
nodeid = rep.nodeid
for checker, before, after in self.leaks[nodeid]:
tr.line(
f"{rep.nodeid} leaking {checker.name}: "
f"{checker.format(before, after)}"
)
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