Auto-updating script for Windows toolchain

tools/win/toolchain/get_toolchain_if_necessary.py

+# Copyright 2013 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import hashlib
+import os
+import subprocess
+import sys
+
+
+BASEDIR = os.path.abspath(os.path.dirname(__file__))

[M-A Ruel, 2013/11/26 17:48:18]

BASEDIR = os.path.dirname(os.path.abspath(__file__))

order is important

[scottmg, 2013/11/26 17:57:54]

Done.

When does it matter? os.path.abspath('') == os.getcwd()

[M-A Ruel, 2013/11/26 18:03:40]

but os.path.dirname(os.getcwd()) != os.path.dirname('')

+
+
+def CalculateHash(root):
+  """Calculates the sha1 of the paths to all files in the given |root| and the
+  contents of those files, and returns as a hex string."""
+  digest = hashlib.sha1()
+  count = 0
+  for root, dirs, files in os.walk(root):
+    dirs.sort()
+    for name in sorted(f.lower() for f in files):
+      path = os.path.normpath(os.path.join(root, name))
+      with open(path, 'rb') as f:
+        digest.update(path.lower())

[M-A Ruel, 2013/11/26 17:48:18]

I'd prefer this to be outside of the with statement.

[scottmg, 2013/11/26 17:57:54]

Done.

+        digest.update(f.read())
+  return digest.hexdigest()
+
+
+def main():
+  if sys.platform not in ('win32', 'cygwin'):
+    return 0
+
+  if len(sys.argv) != 1:
+    print >> sys.stderr, 'Unexpected arguments.'
+    return 1
+
+  # Move to same location as .gclient. This is a no-op when run via gclient.
+  os.chdir(os.path.normpath(os.path.join(BASEDIR, '../../../..')))
+  toolchain_dir = 'src/third_party/win_toolchain'
+  target_dir = os.path.join(toolchain_dir, 'files')
+
+  sha1path = os.path.join(toolchain_dir, 'toolchain.sha1')
+  desired_hash = ''
+  if os.path.isfile(sha1path):
+    with open(sha1path, 'rb') as f:
+      desired_hash = f.read().strip()
+
+  # If the current hash doesn't match what we want in the file, nuke and pave.
+  # Note that this script is only run when a .sha1 file is updated (per DEPS)
+  # so this relatively expensive step of hashing everything only happens when
+  # the toolchain is updated.
+  current_hash = CalculateHash(target_dir)

[M-A Ruel, 2013/11/26 17:48:18]

How long does it take in practice on a spinning drive? If it is significant, it
could be worth keeping a cache of the files timestamps.

[scottmg, 2013/11/26 17:57:54]

Spinning disk, pssh. Can you even build chrome on one of those?

It's about 8s on SSD. I guess worthwhile to cache.

[M-A Ruel, 2013/11/26 18:03:40]

That's 90% of build slaves.
If you could do a test on a cold spinning disk, it'd be appreciated.

+  if current_hash != desired_hash:
+    print 'Windows toolchain out of date or doesn\'t exist, updating...'
+    if os.path.isdir(target_dir):
+      subprocess.check_call('rmdir /s/q "%s"' % target_dir, shell=True)
+    subprocess.check_call([
+        sys.executable,
+        'src/tools/win/toolchain/toolchain2013.py',
+        '--targetdir', target_dir])
+
+  current_hash = CalculateHash(target_dir)
+  if current_hash != desired_hash:
+    print >> sys.stderr, (
+        'Got wrong hash after pulling a new toolchain. '
+        'Wanted \'%s\', got \'%s\'.' % (
+            desired_hash, current_hash))
+    return 1
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())