Bug 1251870 - Disable indexing of objdir on Windows; r=ted

The Windows content indexing service has been known to scan the objdir.
This can add significant system overhead and slow down builds or
subsequent operations. The objdir is meant to be a short-lived black box
and there really isn't a major benefit to indexing it.

There is a file attribute on Windows that disables content indexing.
This commit adds a utility function for creating a directory and
optionally disabling indexing on it. We call it at the top of
`mach build` to ensure the objdir as content indexing disabled.

MozReview-Commit-ID: 68gxCxbkVAN

python/mozbuild/mozbuild/mach_commands.py

@@ -305,7 +305,10 @@ class Build(MachCommandBase):
         """
         import which
         from mozbuild.controller.building import BuildMonitor
-        from mozbuild.util import resolve_target_to_make
+        from mozbuild.util import (
+            mkdir,
+            resolve_target_to_make,
+        )
 
         self.log_manager.register_structured_logger(logging.getLogger('mozbuild'))
 
@@ -314,6 +317,10 @@ class Build(MachCommandBase):
         monitor.init(warnings_path)
         ccache_start = monitor.ccache_stats()
 
+        # Disable indexing in objdir because it is not necessary and can slow
+        # down builds.
+        mkdir(self.topobjdir, not_indexed=True)
+
         with BuildOutputManager(self.log_manager, monitor) as output:
             monitor.start()
 

python/mozbuild/mozbuild/util.py

@@ -9,6 +9,7 @@ from __future__ import absolute_import, unicode_literals
 
 import argparse
 import collections
+import ctypes
 import difflib
 import errno
 import functools
@@ -36,6 +37,11 @@ if sys.version_info[0] == 3:
 else:
     str_type = basestring
 
+if sys.platform == 'win32':
+    _kernel32 = ctypes.windll.kernel32
+    _FILE_ATTRIBUTE_NOT_CONTENT_INDEXED = 0x2000
+
+
 def hash_file(path, hasher=None):
     """Hashes a file specified by the path given and returns the hex digest."""
 
@@ -111,6 +117,28 @@ def ensureParentDir(path):
                 raise
 
 
+def mkdir(path, not_indexed=False):
+    """Ensure a directory exists.
+
+    If ``not_indexed`` is True, an attribute is set that disables content
+    indexing on the directory.
+    """
+    try:
+        os.makedirs(path)
+    except OSError as e:
+        if e.errno != errno.EEXIST:
+            raise
+
+    if not_indexed:
+        if sys.platform == 'win32':
+            if isinstance(path, str_type):
+                fn = _kernel32.SetFileAttributesW
+            else:
+                fn = _kernel32.SetFileAttributesA
+
+            fn(path, _FILE_ATTRIBUTE_NOT_CONTENT_INDEXED)
+
+
 def simple_diff(filename, old_lines, new_lines):
     """Returns the diff between old_lines and new_lines, in unified diff form,
     as a list of lines.