Do not update cache from xdist worker (#10641)

AUTHORS

@@ -315,6 +315,7 @@ Samuel Searles-Bryant
 Samuele Pedroni
 Sanket Duthade
 Sankt Petersbug
+Saravanan Padmanaban
 Segev Finer
 Serhii Mozghovyi
 Seth Junot

changelog/10641.bugfix.rst

@@ -0,0 +1 @@
+Fix a race condition when creating or updating the stepwise plugin's cache, which could occur when multiple xdist worker nodes try to simultaneously update the stepwise plugin's cache.

src/_pytest/stepwise.py

@@ -48,6 +48,10 @@ def pytest_configure(config: Config) -> None:
 def pytest_sessionfinish(session: Session) -> None:
     if not session.config.getoption("stepwise"):
         assert session.config.cache is not None
+        if hasattr(session.config, "workerinput"):
+            # Do not update cache if this process is a xdist worker to prevent
+            # race conditions (#10641).
+            return
         # Clear the list of failing tests if the plugin is not active.
         session.config.cache.set(STEPWISE_CACHE_DIR, [])
 
@@ -119,4 +123,8 @@ class StepwisePlugin:
         return None
 
     def pytest_sessionfinish(self) -> None:
+        if hasattr(self.config, "workerinput"):
+            # Do not update cache if this process is a xdist worker to prevent
+            # race conditions (#10641).
+            return
         self.cache.set(STEPWISE_CACHE_DIR, self.lastfailed)

testing/test_stepwise.py

@@ -1,6 +1,10 @@
+from pathlib import Path
+
 import pytest
+from _pytest.cacheprovider import Cache
 from _pytest.monkeypatch import MonkeyPatch
 from _pytest.pytester import Pytester
+from _pytest.stepwise import STEPWISE_CACHE_DIR
 
 
 @pytest.fixture
@@ -278,3 +282,76 @@ def test_stepwise_skip_is_independent(pytester: Pytester) -> None:
 def test_sw_skip_help(pytester: Pytester) -> None:
     result = pytester.runpytest("-h")
     result.stdout.fnmatch_lines("*Implicitly enables --stepwise.")
+
+
+def test_stepwise_xdist_dont_store_lastfailed(pytester: Pytester) -> None:
+    pytester.makefile(
+        ext=".ini",
+        pytest=f"[pytest]\ncache_dir = {pytester.path}\n",
+    )
+
+    pytester.makepyfile(
+        conftest="""
+import pytest
+
+@pytest.hookimpl(tryfirst=True)
+def pytest_configure(config) -> None:
+    config.workerinput = True
+"""
+    )
+    pytester.makepyfile(
+        test_one="""
+def test_one():
+    assert False
+"""
+    )
+    result = pytester.runpytest("--stepwise")
+    assert result.ret == pytest.ExitCode.INTERRUPTED
+
+    stepwise_cache_file = (
+        pytester.path / Cache._CACHE_PREFIX_VALUES / STEPWISE_CACHE_DIR
+    )
+    assert not Path(stepwise_cache_file).exists()
+
+
+def test_disabled_stepwise_xdist_dont_clear_cache(pytester: Pytester) -> None:
+    pytester.makefile(
+        ext=".ini",
+        pytest=f"[pytest]\ncache_dir = {pytester.path}\n",
+    )
+
+    stepwise_cache_file = (
+        pytester.path / Cache._CACHE_PREFIX_VALUES / STEPWISE_CACHE_DIR
+    )
+    stepwise_cache_dir = stepwise_cache_file.parent
+    stepwise_cache_dir.mkdir(exist_ok=True, parents=True)
+
+    stepwise_cache_file_relative = f"{Cache._CACHE_PREFIX_VALUES}/{STEPWISE_CACHE_DIR}"
+
+    expected_value = '"test_one.py::test_one"'
+    content = {f"{stepwise_cache_file_relative}": expected_value}
+
+    pytester.makefile(ext="", **content)
+
+    pytester.makepyfile(
+        conftest="""
+import pytest
+
+@pytest.hookimpl(tryfirst=True)
+def pytest_configure(config) -> None:
+    config.workerinput = True
+"""
+    )
+    pytester.makepyfile(
+        test_one="""
+def test_one():
+    assert True
+"""
+    )
+    result = pytester.runpytest()
+    assert result.ret == 0
+
+    assert Path(stepwise_cache_file).exists()
+    with stepwise_cache_file.open() as file_handle:
+        observed_value = file_handle.readlines()
+    assert [expected_value] == observed_value