Lock parallel package operations

This ensures that two tox invocation on different target environments will work.

Signed-off-by: Bernát Gábor <bgabor8@bloomberg.net>

.pre-commit-config.yaml

@@ -59,7 +59,7 @@ repos:
           - flake8-unused-arguments==0.0.12
           - flake8-noqa==1.3
           - pep8-naming==0.13.2
-          - flake8-pyproject==1.2.1
+          - flake8-pyproject==1.2.2
   - repo: https://github.com/pre-commit/mirrors-prettier
     rev: "v2.7.1"
     hooks:

docs/changelog/2594.bugfix.rst

@@ -0,0 +1,2 @@
+Ensure that two parallel tox instance invocations on different tox environment targets will work by holding a file lock
+onto the packaging operations (e.g., in bash ``tox4 r -e py311 &; tox4 r -e py310``) - by :user:`gaborbernat`.

pyproject.toml

@@ -30,6 +30,7 @@ dependencies = [
   "pyproject-api>=1.2.1",
   'tomli>=2.0.1; python_version < "3.11"',
   "virtualenv>=20.17",
+  "filelock>=3.8.1",
   'importlib-metadata>=5.1; python_version < "3.8"',
   'typing-extensions>=4.4; python_version < "3.8"',
 ]
@@ -49,7 +50,6 @@ optional-dependencies.testing = [
   "devpi-process>=0.3",
   "diff-cover>=7.2",
   "distlib>=0.3.6",
-  "filelock>=3.8",
   "flaky>=3.7",
   "hatch-vcs>=0.2",
   "hatchling>=1.11.1",

src/tox/tox_env/package.py

@@ -9,6 +9,8 @@
 from types import MethodType
 from typing import TYPE_CHECKING, Any, Callable, Generator, Iterator, cast
 
+from filelock import FileLock
+
 from tox.config.main import Config
 from tox.config.sets import EnvConfigSet
 
@@ -31,29 +33,39 @@ def __str__(self) -> str:
         return str(self.path)
 
 
-def _lock_method(lock: RLock, meth: Callable[..., Any]) -> Callable[..., Any]:
+def _lock_method(thread_lock: RLock, file_lock: FileLock | None, meth: Callable[..., Any]) -> Callable[..., Any]:
     def _func(*args: Any, **kwargs: Any) -> Any:
-        with lock:
-            return meth(*args, **kwargs)
+        with thread_lock:
+            if file_lock is not None and file_lock.is_locked is False:  # file_lock is to lock from other tox processes
+                file_lock.acquire()
+            try:
+                return meth(*args, **kwargs)
+            finally:
+                if file_lock is not None:
+                    file_lock.release()
 
     return _func
 
 
 class PackageToxEnv(ToxEnv, ABC):
     def __init__(self, create_args: ToxEnvCreateArgs) -> None:
-        self._lock = RLock()
+        self._thread_lock = RLock()
+        self._file_lock: FileLock | None = None
         super().__init__(create_args)
         self._envs: set[str] = set()
 
     def __getattribute__(self, name: str) -> Any:
         # the packaging class might be used by multiple environments in parallel, hold a lock for operations on it
         obj = object.__getattribute__(self, name)
         if isinstance(obj, MethodType):
-            obj = _lock_method(self._lock, obj)
+            obj = _lock_method(self._thread_lock, self._file_lock, obj)
         return obj
 
     def register_config(self) -> None:
         super().register_config()
+        file_lock_path: Path = self.conf["env_dir"] / "file.lock"
+        self._file_lock = FileLock(file_lock_path)
+        file_lock_path.parent.mkdir(parents=True, exist_ok=True)
         self.core.add_config(
             keys=["package_root", "setupdir"],
             of_type=Path,