Adding darwin.py platform

Adding functionality to recognise Darwin as a platform in plaform.py

buildstream/_platform/darwin.py

+#
+#  Copyright (C) 2017 Codethink Limited
+#  Copyright (C) 2018 Bloomberg Finance LP
+#
+#  This program is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU Lesser General Public
+#  License as published by the Free Software Foundation; either
+#  version 2 of the License, or (at your option) any later version.
+#
+#  This library is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+#  Lesser General Public License for more details.
+#
+#  You should have received a copy of the GNU Lesser General Public
+#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
+
+import os
+import resource
+
+from .._artifactcache.cascache import CASCache
+from .._exceptions import PlatformError
+from ..sandbox import SandboxChroot
+
+from . import Platform
+
+
+class Darwin(Platform):
+
+    def __init__(self, context):
+
+        super().__init__(context)
+        self._artifact_cache = CASCache(context)
+
+        # Need to set resources for _frontend/app.py as this is dependent on the platform
+        # SafeHardlinks FUSE needs to hold file descriptors for all processes in the sandbox.
+        # Avoid hitting the limit too quickly.
+        limits = resource.getrlimit(resource.RLIMIT_NOFILE)
+        if limits[0] != limits[1]:
+            resource.setrlimit(resource.RLIMIT_NOFILE, (49152, limits[1]))
+
+        # Not necessarily 100% reliable, but we want to fail early.
+        if os.geteuid() != 0:
+            raise PlatformError("Root privileges are required to run without bubblewrap.")
+
+    @property
+    def artifactcache(self):
+        return self._artifact_cache
+
+    def create_sandbox(self, *args, **kwargs):
+        return SandboxChroot(*args, **kwargs)

buildstream/_platform/platform.py

@@ -40,19 +40,23 @@ class Platform():
 
     @classmethod
     def create_instance(cls, *args, **kwargs):
-        if sys.platform.startswith('linux'):
-            backend = 'linux'
-        else:
-            backend = 'unix'
 
         # Meant for testing purposes and therefore hidden in the
         # deepest corners of the source code. Try not to abuse this,
         # please?
         if os.getenv('BST_FORCE_BACKEND'):
             backend = os.getenv('BST_FORCE_BACKEND')
+        elif sys.platform.startswith('linux'):
+            backend = 'linux'
+        elif sys.platform.startswith('darwin'):
+            backend = 'darwin'
+        else:
+            backend = 'unix'
 
         if backend == 'linux':
             from .linux import Linux as PlatformImpl
+        elif backend == 'darwin':
+            from .darwin import Darwin as PlatformImpl
         elif backend == 'unix':
             from .unix import Unix as PlatformImpl
         else: