WIP: wrap: Implemented wraplock

mesonbuild/wrap/wrap.py

@@ -28,6 +28,7 @@
 from functools import lru_cache
 
 from . import WrapMode
+from .wraplock import WrapLock
 from .. import coredata
 from ..mesonlib import quiet_git, GIT, ProgressBar, MesonException, windows_proof_rmtree, Popen_safe
 from ..interpreterbase import FeatureNew
@@ -304,6 +305,7 @@ class Resolver:
     def __post_init__(self) -> None:
         self.subdir_root = os.path.join(self.source_dir, self.subdir)
         self.cachedir = os.environ.get('MESON_PACKAGE_CACHE_DIR') or os.path.join(self.subdir_root, 'packagecache')
+        self.wraplock = WrapLock(self.subdir_root)
         self.wraps: T.Dict[str, PackageDefinition] = {}
         self.netrc: T.Optional[netrc] = None
         self.provided_deps: T.Dict[str, PackageDefinition] = {}
@@ -427,7 +429,7 @@ def find_program_provider(self, names: T.List[str]) -> T.Optional[str]:
                 return wrap_name
         return None
 
-    def resolve(self, packagename: str, force_method: T.Optional[Method] = None) -> T.Tuple[str, Method]:
+    def _resolve(self, packagename: str, force_method: T.Optional[Method]) -> T.Tuple[str, Method]:
         wrap = self.wraps.get(packagename)
         if wrap is None:
             wrap = self.get_from_wrapdb(packagename)
@@ -525,6 +527,10 @@ def has_buildfile() -> bool:
         self.wrap.update_hash_cache(self.dirname)
         return rel_path, method
 
+    def resolve(self, packagename: str, force_method: T.Optional[Method] = None) -> T.Tuple[str, Method]:
+        with self.wraplock:
+            return self._resolve(packagename, force_method)
+
     def check_can_download(self) -> None:
         # Don't download subproject data based on wrap file if requested.
         # Git submodules are ok (see above)!

mesonbuild/wrap/wraplock.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+import os
+
+try:
+    import fcntl
+except ImportError:
+    class WrapLock():
+        def __init__(self, subdir_root: str):
+            pass
+        def __enter__(self, *args, **kwargs) -> None:
+            pass
+        def __exit__(self, *args, **kwargs) -> None:
+            pass
+else:
+    class WrapLock():
+        def __init__(self, subdir_root: str):
+            self.lock_file = os.path.join(subdir_root, ".wraplock")
+
+        """Uses the :func:`fcntl.flock` to hard lock the lock file on unix systems."""
+        def __enter__(self, *args, **kwargs) -> None:
+            try:
+                self.fd = os.open(self.lock_file,
+                             os.O_RDWR | os.O_TRUNC | os.O_CREAT,
+                             0o644);
+            except FileNotFoundError:
+                self.fd = -1
+                return
+            fcntl.flock(self.fd, fcntl.LOCK_EX)
+
+        def __exit__(self, *args, **kwargs) -> None:
+            if self.fd == -1:
+                return;
+            # Do not remove the lockfile:
+            #   https://github.com/tox-dev/py-filelock/issues/31
+            #   https://stackoverflow.com/questions/17708885/flock-removing-locked-file-without-race-condition
+            fcntl.flock(self.fd, fcntl.LOCK_UN)
+            os.close(self.fd)
+            self.fd = -1
+
+__all__ = [
+    "WrapLock",
+]

test cases/unit/116 empty project/expected_mods.json

@@ -237,7 +237,8 @@
       "mesonbuild.utils.universal",
       "mesonbuild.utils.vsenv",
       "mesonbuild.wrap",
-      "mesonbuild.wrap.wrap"
+      "mesonbuild.wrap.wrap",
+      "mesonbuild.wrap.wraplock"
     ],
     "count": 69
   }