Measure resident memory in leak tests, not peak memory

* ru_maxrss never falls, so leak tests were measuring occasional transient
  spikes, not true leaks. Instead, for leak tests we now read the current
  RSS, which falls (to a degree, depending on system allocator strategy)
  when memory is released, and also doesn't depend on the process's past.
* The tests' limits were adjusted based on empirical measurements.

Author: akx

.ci/requirements-mypy.txt

@@ -12,4 +12,5 @@ pytest
 types-atheris
 types-defusedxml
 types-olefile
+types-psutil
 types-setuptools

Tests/helper.py

@@ -22,8 +22,15 @@
 if TYPE_CHECKING:
     from collections.abc import Callable, Sequence
     from pathlib import Path
+    from types import ModuleType
     from typing import Any
 
+psutil: ModuleType | None
+try:
+    import psutil
+except ImportError:
+    psutil = None
+
 logger = logging.getLogger(__name__)
 
 uploader = None
@@ -212,33 +219,33 @@ def is_pypy() -> bool:
 
 
 @pytest.mark.isolated
-@pytest.mark.skipif(sys.platform.startswith("win32"), reason="Requires Unix or macOS")
+@pytest.mark.skipif(psutil is None, reason="psutil not installed")
+@pytest.mark.skipif(
+    sys.platform.startswith("win32"),
+    reason="Leak limits are not calibrated for Windows",
+)
 # Per https://stackoverflow.com/a/29007723/51685, due to JIT compilation,
 # RSS utilization is known to grow in PyPy.
 @pytest.mark.skipif(is_pypy(), reason="max RSS utilization is not stable on PyPy")
 class PillowLeakTestCase:
-    # requires unix/macOS
     iterations = 100  # count
     mem_limit = 512  # k
 
     def _get_mem_usage(self) -> float:
         """
-        Gets the RUSAGE memory usage, returns in K. Encapsulates the difference
-        between macOS and Linux rss reporting
+        Gets the resident set size currently used by this process.
 
         :returns: memory usage in kilobytes
         """
 
-        from resource import RUSAGE_SELF, getrusage
-
-        mem = getrusage(RUSAGE_SELF).ru_maxrss
-        # man 2 getrusage:
-        #     ru_maxrss
-        # This is the maximum resident set size utilized
-        # in bytes on macOS, in kilobytes on Linux
-        return mem / 1024 if sys.platform == "darwin" else mem
+        assert psutil is not None
+        return psutil.Process().memory_info().rss / 1024
 
     def _test_leak(self, core: Callable[[], None]) -> None:
+        # Warm up so allocator arenas, caches, etc. are allocated,
+        # before taking the baseline measurement.
+        core()
+
         start_mem = self._get_mem_usage()
         for cycle in range(self.iterations):
             core()

Tests/test_font_leaks.py

@@ -23,9 +23,8 @@ def _test_font(self, font: ImageFont.FreeTypeFont | ImageFont.ImageFont) -> None
 
 
 class TestTTypeFontLeak(TestFontLeak):
-    # fails at iteration 3 in main
-    iterations = 10
-    mem_limit = 4096  # k
+    iterations = 30
+    mem_limit = 32768  # k
 
     @skip_unless_feature("freetype2")
     def test_leak(self) -> None:
@@ -34,9 +33,8 @@ def test_leak(self) -> None:
 
 
 class TestDefaultFontLeak(TestFontLeak):
-    # fails at iteration 37 in main
-    iterations = 100
-    mem_limit = 1024  # k
+    iterations = 1000
+    mem_limit = 16384  # k
 
     def test_leak(self, monkeypatch: pytest.MonkeyPatch) -> None:
         if features.check_module("freetype2"):

pyproject.toml

@@ -71,6 +71,7 @@ optional-dependencies.tests = [
   "markdown2",
   "olefile",
   "packaging",
+  "psutil; sys_platform=='darwin' or sys_platform=='linux'",
   "pytest",
   "pytest-cov",
   "pytest-timeout",