Limit repository creation to one process

pre_commit/file_lock.py

@@ -0,0 +1,53 @@
+import contextlib
+import errno
+
+
+try:  # pragma: no cover (windows)
+    import msvcrt
+
+    # https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/locking
+
+    # on windows we lock "regions" of files, we don't care about the actual
+    # byte region so we'll just pick *some* number here.
+    _region = 0xffff
+
+    @contextlib.contextmanager
+    def _locked(fileno):
+        while True:
+            try:
+                msvcrt.locking(fileno, msvcrt.LK_LOCK, _region)
+            except OSError as e:
+                # Locking violation. Returned when the _LK_LOCK or _LK_RLCK
+                # flag is specified and the file cannot be locked after 10
+                # attempts.
+                if e.errno != errno.EDEADLOCK:
+                    raise
+            else:
+                break
+
+        try:
+            yield
+        finally:
+            # From cursory testing, it seems to get unlocked when the file is
+            # closed so this may not be necessary.
+            # The documentation however states:
+            # "Regions should be locked only briefly and should be unlocked
+            # before closing a file or exiting the program."
+            msvcrt.locking(fileno, msvcrt.LK_UNLCK, _region)
+except ImportError:  # pragma: no cover (posix)
+    import fcntl
+
+    @contextlib.contextmanager
+    def _locked(fileno):
+        fcntl.flock(fileno, fcntl.LOCK_EX)
+        try:
+            yield
+        finally:
+            fcntl.flock(fileno, fcntl.LOCK_UN)
+
+
+@contextlib.contextmanager
+def lock(path):
+    with open(path, 'a+') as f:
+        with _locked(f.fileno()):
+            yield

pre_commit/repository.py

@@ -64,34 +64,42 @@ def _installed(cmd_runner, language_name, language_version, additional_deps):
     )
 
 
-def _install_all(venvs, repo_url):
+def _install_all(venvs, repo_url, store):
     """Tuple of (cmd_runner, language, version, deps)"""
-    need_installed = tuple(
-        (cmd_runner, language_name, version, deps)
-        for cmd_runner, language_name, version, deps in venvs
-        if not _installed(cmd_runner, language_name, version, deps)
-    )
+    def _need_installed():
+        return tuple(
+            (cmd_runner, language_name, version, deps)
+            for cmd_runner, language_name, version, deps in venvs
+            if not _installed(cmd_runner, language_name, version, deps)
+        )
+
+    if not _need_installed():
+        return
+    with store.exclusive_lock():
+        # Another process may have already completed this work
+        need_installed = _need_installed()
+        if not need_installed:  # pragma: no cover (race)
+            return
 
-    if need_installed:
         logger.info(
             'Installing environment for {}.'.format(repo_url),
         )
         logger.info('Once installed this environment will be reused.')
         logger.info('This may take a few minutes...')
 
-    for cmd_runner, language_name, version, deps in need_installed:
-        language = languages[language_name]
-        venv = environment_dir(language.ENVIRONMENT_DIR, version)
+        for cmd_runner, language_name, version, deps in need_installed:
+            language = languages[language_name]
+            venv = environment_dir(language.ENVIRONMENT_DIR, version)
 
-        # There's potentially incomplete cleanup from previous runs
-        # Clean it up!
-        if cmd_runner.exists(venv):
-            shutil.rmtree(cmd_runner.path(venv))
+            # There's potentially incomplete cleanup from previous runs
+            # Clean it up!
+            if cmd_runner.exists(venv):
+                shutil.rmtree(cmd_runner.path(venv))
 
-        language.install_environment(cmd_runner, version, deps)
-        # Write our state to indicate we're installed
-        state = _state(deps)
-        _write_state(cmd_runner, venv, state)
+            language.install_environment(cmd_runner, version, deps)
+            # Write our state to indicate we're installed
+            state = _state(deps)
+            _write_state(cmd_runner, venv, state)
 
 
 def _validate_minimum_version(hook):
@@ -174,7 +182,7 @@ class Repository(object):
 
     def require_installed(self):
         if not self.__installed:
-            _install_all(self._venvs, self.repo_config['repo'])
+            _install_all(self._venvs, self.repo_config['repo'], self.store)
             self.__installed = True
 
     def run_hook(self, hook, file_args):

pre_commit/store.py

@@ -10,6 +10,7 @@ import tempfile
 from cached_property import cached_property
 
 import pre_commit.constants as C
+from pre_commit import file_lock
 from pre_commit.prefixed_command_runner import PrefixedCommandRunner
 from pre_commit.util import clean_path_on_failure
 from pre_commit.util import cmd_output
@@ -37,13 +38,20 @@ def _get_default_directory():
 
 class Store(object):
     get_default_directory = staticmethod(_get_default_directory)
+    __created = False
 
     def __init__(self, directory=None):
         if directory is None:
             directory = self.get_default_directory()
 
         self.directory = directory
-        self.__created = False
+
+    @contextlib.contextmanager
+    def exclusive_lock(self, quiet=False):
+        if not quiet:
+            logger.info('Locking pre-commit directory')
+        with file_lock.lock(os.path.join(self.directory, '.lock')):
+            yield
 
     def _write_readme(self):
         with io.open(os.path.join(self.directory, 'README'), 'w') as readme:
@@ -75,12 +83,17 @@ class Store(object):
         os.rename(tmpfile, self.db_path)
 
     def _create(self):
-        if os.path.exists(self.db_path):
-            return
         if not os.path.exists(self.directory):
             os.makedirs(self.directory)
             self._write_readme()
-        self._write_sqlite_db()
+
+        if os.path.exists(self.db_path):
+            return
+        with self.exclusive_lock(quiet=True):
+            # Another process may have already completed this work
+            if os.path.exists(self.db_path):  # pragma: no cover (race)
+                return
+            self._write_sqlite_db()
 
     def require_created(self):
         """Require the pre-commit file store to be created."""
@@ -91,27 +104,37 @@ class Store(object):
     def _new_repo(self, repo, ref, make_strategy):
         self.require_created()
 
-        # Check if we already exist
-        with sqlite3.connect(self.db_path) as db:
-            result = db.execute(
-                'SELECT path FROM repos WHERE repo = ? AND ref = ?',
-                [repo, ref],
-            ).fetchone()
-            if result:
-                return result[0]
+        def _get_result():
+            # Check if we already exist
+            with sqlite3.connect(self.db_path) as db:
+                result = db.execute(
+                    'SELECT path FROM repos WHERE repo = ? AND ref = ?',
+                    [repo, ref],
+                ).fetchone()
+                if result:
+                    return result[0]
 
-        logger.info('Initializing environment for {}.'.format(repo))
+        result = _get_result()
+        if result:
+            return result
+        with self.exclusive_lock():
+            # Another process may have already completed this work
+            result = _get_result()
+            if result:  # pragma: no cover (race)
+                return result
 
-        directory = tempfile.mkdtemp(prefix='repo', dir=self.directory)
-        with clean_path_on_failure(directory):
-            make_strategy(directory)
+            logger.info('Initializing environment for {}.'.format(repo))
 
-        # Update our db with the created repo
-        with sqlite3.connect(self.db_path) as db:
-            db.execute(
-                'INSERT INTO repos (repo, ref, path) VALUES (?, ?, ?)',
-                [repo, ref, directory],
-            )
+            directory = tempfile.mkdtemp(prefix='repo', dir=self.directory)
+            with clean_path_on_failure(directory):
+                make_strategy(directory)
+
+            # Update our db with the created repo
+            with sqlite3.connect(self.db_path) as db:
+                db.execute(
+                    'INSERT INTO repos (repo, ref, path) VALUES (?, ?, ?)',
+                    [repo, ref, directory],
+                )
         return directory
 
     def clone(self, repo, ref):

tests/commands/install_uninstall_test.py

@@ -142,7 +142,8 @@ FILES_CHANGED = (
 
 
 NORMAL_PRE_COMMIT_RUN = re.compile(
-    r'^\[INFO\] Initializing environment for .+\.\r?\n'
+    r'^\[INFO\] Locking pre-commit directory\r?\n'
+    r'\[INFO\] Initializing environment for .+\.\r?\n'
     r'Bash hook\.+Passed\r?\n'
     r'\[master [a-f0-9]{7}\] Commit!\r?\n' +
     FILES_CHANGED +
@@ -254,7 +255,8 @@ def test_environment_not_sourced(tempdir_factory):
 
 
 FAILING_PRE_COMMIT_RUN = re.compile(
-    r'^\[INFO\] Initializing environment for .+\.\r?\n'
+    r'^\[INFO\] Locking pre-commit directory\r?\n'
+    r'\[INFO\] Initializing environment for .+\.\r?\n'
     r'Failing hook\.+Failed\r?\n'
     r'hookid: failing_hook\r?\n'
     r'\r?\n'
@@ -332,6 +334,7 @@ def test_install_existing_hook_no_overwrite_idempotent(tempdir_factory):
 
 FAIL_OLD_HOOK = re.compile(
     r'fail!\r?\n'
+    r'\[INFO\] Locking pre-commit directory\r?\n'
     r'\[INFO\] Initializing environment for .+\.\r?\n'
     r'Bash hook\.+Passed\r?\n',
 )

tests/repository_test.py

@@ -547,8 +547,8 @@ def test_reinstall(tempdir_factory, store, log_info_mock):
     config = make_config_from_repo(path)
     repo = Repository.create(config, store)
     repo.require_installed()
-    # We print some logging during clone (1) + install (3)
-    assert log_info_mock.call_count == 4
+    # We print some logging during clone (2) + install (4)
+    assert log_info_mock.call_count == 6
     log_info_mock.reset_mock()
     # Reinstall with same repo should not trigger another install
     repo.require_installed()

tests/store_test.py

@@ -88,7 +88,7 @@ def test_clone(store, tempdir_factory, log_info_mock):
 
     ret = store.clone(path, sha)
     # Should have printed some stuff
-    assert log_info_mock.call_args_list[0][0][0].startswith(
+    assert log_info_mock.call_args_list[1][0][0].startswith(
         'Initializing environment for ',
     )