utils: Replace BuildDirLock with generic DirectoryLock

DirectoryLock provides a generic locking implementation the replaces the
previously used BuildDirLock.

.gitignore

@@ -22,6 +22,7 @@ __pycache__
 *~
 *.swp
 packagecache
+.wraplock
 /MANIFEST
 /build
 /dist

mesonbuild/msetup.py

@@ -184,7 +184,9 @@ def generate(self, capture: bool = False, vslite_ctx: T.Optional[dict] = None) -
             mlog.set_timestamp_start(time.monotonic())
         if self.options.clearcache:
             env.coredata.clear_cache()
-        with mesonlib.BuildDirLock(self.build_dir):
+        with mesonlib.DirectoryLock(self.build_dir, 'meson-private/meson.lock',
+                                    mesonlib.DirectoryLockAction.FAIL,
+                                    'Some other Meson process is already using this build directory. Exiting.'):
             return self._generate(env, capture, vslite_ctx)
 
     def _generate(self, env: environment.Environment, capture: bool, vslite_ctx: T.Optional[dict]) -> T.Optional[dict]:

mesonbuild/utils/platform.py

@@ -6,22 +6,27 @@
 
 """base classes providing no-op functionality.."""
 
+import enum
 import os
 import typing as T
 
 from .. import mlog
 
-__all__ = ['BuildDirLock']
+__all__ = ['DirectoryLock', 'DirectoryLockAction']
 
-# This needs to be inherited by the specific implementations to make type
-# checking happy
-class BuildDirLock:
+class DirectoryLockAction(enum.Enum):
+    IGNORE = 0
+    WAIT = 1
+    FAIL = 2
 
-    def __init__(self, builddir: str) -> None:
-        self.lockfilename = os.path.join(builddir, 'meson-private/meson.lock')
+class DirectoryLock:
+    def __init__(self, directory: str, lockfile: str, action: DirectoryLockAction, err: str) -> None:
+        self.action = action
+        self.err = err
+        self.lockpath = os.path.join(directory, lockfile)
 
     def __enter__(self) -> None:
-        mlog.debug('Calling the no-op version of BuildDirLock')
+        mlog.debug('Calling the no-op version of DirectoryLock')
 
     def __exit__(self, *args: T.Any) -> None:
         pass

mesonbuild/utils/posix.py

@@ -10,23 +10,38 @@
 import typing as T
 
 from .core import MesonException
-from .platform import BuildDirLock as BuildDirLockBase
+from .platform import DirectoryLock as DirectoryLockBase, DirectoryLockAction
 
-__all__ = ['BuildDirLock']
+__all__ = ['DirectoryLock', 'DirectoryLockAction']
 
-class BuildDirLock(BuildDirLockBase):
+class DirectoryLock(DirectoryLockBase):
 
     def __enter__(self) -> None:
-        self.lockfile = open(self.lockfilename, 'w', encoding='utf-8')
         try:
-            fcntl.flock(self.lockfile, fcntl.LOCK_EX | fcntl.LOCK_NB)
-        except (BlockingIOError, PermissionError):
+            self.lockfile = open(self.lockpath, 'w+', encoding='utf-8')
+        except FileNotFoundError:
+            self.lockfile = None
+            return
+
+        try:
+            flags = fcntl.LOCK_EX
+            if self.action != DirectoryLockAction.WAIT:
+                flags = flags | fcntl.LOCK_NB
+            fcntl.flock(self.lockfile, flags)
+        except BlockingIOError:
+            self.lockfile.close()
+            if self.action == DirectoryLockAction.IGNORE:
+                return
+            raise MesonException(self.err)
+        except PermissionError:
             self.lockfile.close()
-            raise MesonException('Some other Meson process is already using this build directory. Exiting.')
+            raise MesonException(self.err)
         except OSError as e:
             self.lockfile.close()
-            raise MesonException(f'Failed to lock the build directory: {e.strerror}')
+            raise MesonException(f'Failed to lock directory {self.lockpath}: {e.strerror}')
 
     def __exit__(self, *args: T.Any) -> None:
+        if self.lockfile is None or self.lockfile.closed:
+            return
         fcntl.flock(self.lockfile, fcntl.LOCK_UN)
         self.lockfile.close()

mesonbuild/utils/win32.py

@@ -10,20 +10,35 @@
 import typing as T
 
 from .core import MesonException
-from .platform import BuildDirLock as BuildDirLockBase
+from .platform import DirectoryLock as DirectoryLockBase, DirectoryLockAction
 
-__all__ = ['BuildDirLock']
+__all__ = ['DirectoryLock', 'DirectoryLockAction']
 
-class BuildDirLock(BuildDirLockBase):
+class DirectoryLock(DirectoryLockBase):
 
     def __enter__(self) -> None:
-        self.lockfile = open(self.lockfilename, 'w', encoding='utf-8')
         try:
-            msvcrt.locking(self.lockfile.fileno(), msvcrt.LK_NBLCK, 1)
-        except (BlockingIOError, PermissionError):
+            self.lockfile = open(self.lockpath, 'w+', encoding='utf-8')
+        except FileNotFoundError:
+            self.lockfile = None
+            return
+
+        try:
+            mode = msvcrt.LK_LOCK
+            if self.action != DirectoryLockAction.WAIT:
+                mode = msvcrt.LK_NBLCK
+            msvcrt.locking(self.lockfile.fileno(), mode, 1)
+        except BlockingIOError:
+            self.lockfile.close()
+            if self.action == DirectoryLockAction.IGNORE:
+                return
+            raise MesonException(self.err)
+        except PermissionError:
             self.lockfile.close()
-            raise MesonException('Some other Meson process is already using this build directory. Exiting.')
+            raise MesonException(self.err)
 
     def __exit__(self, *args: T.Any) -> None:
+        if self.lockfile is None or self.lockfile.closed:
+            return
         msvcrt.locking(self.lockfile.fileno(), msvcrt.LK_UNLCK, 1)
         self.lockfile.close()

unittests/allplatformstests.py

@@ -28,7 +28,7 @@
 import mesonbuild.machinefile
 import mesonbuild.modules.gnome
 from mesonbuild.mesonlib import (
-    BuildDirLock, MachineChoice, is_windows, is_osx, is_cygwin, is_dragonflybsd,
+    DirectoryLock, DirectoryLockAction, MachineChoice, is_windows, is_osx, is_cygwin, is_dragonflybsd,
     is_sunos, windows_proof_rmtree, python_command, version_compare, split_args, quote_arg,
     relpath, is_linux, git, search_version, do_conf_file, do_conf_str, default_prefix,
     MesonException, EnvironmentException,
@@ -2447,10 +2447,9 @@ def test_identical_target_name_in_subdir_flat_layout(self):
     def test_flock(self):
         exception_raised = False
         with tempfile.TemporaryDirectory() as tdir:
-            os.mkdir(os.path.join(tdir, 'meson-private'))
-            with BuildDirLock(tdir):
+            with DirectoryLock(tdir, 'lock', DirectoryLockAction.FAIL, 'failed to lock directory'):
                 try:
-                    with BuildDirLock(tdir):
+                    with DirectoryLock(tdir, 'lock', DirectoryLockAction.FAIL, 'expected failure'):
                         pass
                 except MesonException:
                     exception_raised = True