Allow blocking git-cache update with a timeout.

I guess I'm the only developer using git-cache, which is sad.
Hopefully these fixes will make it easier to adapt this to developer
usage some time in the FUTURE.

BUG=583420
TEST=Works for me
R=agable@chromium.org,tandrii@chromium.org

Review URL: https://codereview.chromium.org/1650993005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@298531 0039d316-1c4b-4281-b951-d872f2087c98

gclient.py

@@ -2049,6 +2049,9 @@ def CMDsync(parser, args):
                     help='Don\'t bootstrap from Google Storage.')
   parser.add_option('--ignore_locks', action='store_true',
                     help='GIT ONLY - Ignore cache locks.')
+  parser.add_option('--lock_timeout', type='int', default=0,
+                    help='GIT ONLY - Deadline (in seconds) to wait for git '
+                         'cache lock to become available.')
   (options, args) = parser.parse_args(args)
   client = GClient.LoadCurrentConfig(options)
 

gclient_scm.py

@@ -871,7 +871,8 @@ class GitWrapper(SCMWrapper):
     mirror.populate(verbose=options.verbose,
                     bootstrap=not getattr(options, 'no_bootstrap', False),
                     depth=depth,
-                    ignore_lock=getattr(options, 'ignore_locks', False))
+                    ignore_lock=getattr(options, 'ignore_locks', False),
+                    lock_timeout=getattr(options, 'lock_timeout', 0))
     mirror.unlock()
 
   def _Clone(self, revision, url, options):

git_cache.py

@@ -44,8 +44,9 @@ class RefsHeadsFailedToFetch(Exception):
 class Lockfile(object):
   """Class to represent a cross-platform process-specific lockfile."""
 
-  def __init__(self, path):
+  def __init__(self, path, timeout=0):
     self.path = os.path.abspath(path)
+    self.timeout = timeout
     self.lockfile = self.path + ".lock"
     self.pid = os.getpid()
 
@@ -91,12 +92,22 @@ class Lockfile(object):
   def lock(self):
     """Acquire the lock.
 
-    Note: This is a NON-BLOCKING FAIL-FAST operation.
-    Do. Or do not. There is no try.
+    This will block with a deadline of self.timeout seconds.
+    If self.timeout is zero, this is a NON-BLOCKING FAIL-FAST operation.
     """
+    elapsed = 0
+    while True:
       try:
         self._make_lockfile()
+        return
       except OSError as e:
+        if elapsed < self.timeout:
+          sleep_time = min(3, self.timeout - elapsed)
+          logging.info('Could not create git cache lockfile; '
+                       'will retry after sleep(%d).', sleep_time);
+          elapsed += sleep_time
+          time.sleep(sleep_time)
+          continue
         if e.errno == errno.EEXIST:
           raise LockError("%s is already locked" % self.path)
         else:
@@ -401,13 +412,13 @@ class Mirror(object):
         logging.warn('Fetch of %s failed' % spec)
 
   def populate(self, depth=None, shallow=False, bootstrap=False,
-               verbose=False, ignore_lock=False):
+               verbose=False, ignore_lock=False, lock_timeout=0):
     assert self.GetCachePath()
     if shallow and not depth:
       depth = 10000
     gclient_utils.safe_makedirs(self.GetCachePath())
 
-    lockfile = Lockfile(self.mirror_path)
+    lockfile = Lockfile(self.mirror_path, lock_timeout)
     if not ignore_lock:
       lockfile.lock()
 
@@ -582,6 +593,7 @@ def CMDpopulate(parser, args):
       'shallow': options.shallow,
       'bootstrap': not options.no_bootstrap,
       'ignore_lock': options.ignore_locks,
+      'lock_timeout': options.timeout,
   }
   if options.depth:
     kwargs['depth'] = options.depth
@@ -625,7 +637,8 @@ def CMDfetch(parser, args):
   git_dir = os.path.abspath(git_dir)
   if git_dir.startswith(cachepath):
     mirror = Mirror.FromPath(git_dir)
-    mirror.populate(bootstrap=not options.no_bootstrap)
+    mirror.populate(
+        bootstrap=not options.no_bootstrap, lock_timeout=options.timeout)
     return 0
   for remote in remotes:
     remote_url = subprocess.check_output(
@@ -634,7 +647,8 @@ def CMDfetch(parser, args):
       mirror = Mirror.FromPath(remote_url)
       mirror.print = lambda *args: None
       print('Updating git cache...')
-      mirror.populate(bootstrap=not options.no_bootstrap)
+      mirror.populate(
+          bootstrap=not options.no_bootstrap, lock_timeout=options.timeout)
     subprocess.check_call([Mirror.git_exe, 'fetch', remote])
   return 0
 
@@ -683,6 +697,8 @@ class OptionParser(optparse.OptionParser):
                     help='Increase verbosity (can be passed multiple times)')
     self.add_option('-q', '--quiet', action='store_true',
                     help='Suppress all extraneous output')
+    self.add_option('--timeout', type='int', default=0,
+                    help='Timeout for acquiring cache lock, in seconds')
 
   def parse_args(self, args=None, values=None):
     options, args = optparse.OptionParser.parse_args(self, args, values)