diff options
| -rw-r--r-- | lib/git/utils.py | 36 |
1 files changed, 25 insertions, 11 deletions
diff --git a/lib/git/utils.py b/lib/git/utils.py index 69ee927a..fbc1ea2e 100644 --- a/lib/git/utils.py +++ b/lib/git/utils.py @@ -119,6 +119,10 @@ class LockFile(object): """ return "%s.lock" % (self._file_path) + def _get_id(self): + """Returns string id to be written into the lock file""" + return "%i|%i" % (os.getpid(), hash(self)) + def _has_lock(self): """ Return @@ -133,13 +137,13 @@ class LockFile(object): lock_file = self._lock_file_path() try: fp = open(lock_file, "rb") - pid = int(fp.read()) + pid = fp.read() fp.close() except IOError: raise AssertionError("The lock file at %s could not be read" % lock_file) - if pid != os.getpid(): - raise AssertionError("We claim to own the lock at %s, but it was not owned by our process %i, but by %i" % (lock_file, os.getpid(), pid)) + if pid != self._get_id(): + raise AssertionError("We claim to own the lock at %s, but it was not owned by our process %r, but by %r" % (lock_file, self._get_id(), pid )) return True @@ -152,14 +156,25 @@ class LockFile(object): """ if self._has_lock(): return - lock_file = self._lock_file_path() - if os.path.exists(lock_file): + if os.path.isfile(lock_file): raise IOError("Lock for file %r did already exist, delete %r in case the lock is illegal" % (self._file_path, lock_file)) - + + my_id = self._get_id() fp = open(lock_file, "wb") - fp.write(str(os.getpid())) + fp.write(my_id) + fp.close() + + # verify its truly us who got the lock - if two threads are doing this within the + # fraction of a millisecond, it is possible to actually trick the FS + # and two threads write, but only one succeeds. + fp = open(lock_file, 'rb') + actual_id = fp.read() fp.close() + if actual_id != my_id: + msg = "Failed to obtain lock for file %r as the process identified by %r outraced this process or thread %r" % (self._file_path, actual_id, my_id) + raise IOError(msg) + # END verification self._owns_lock = True @@ -175,11 +190,11 @@ class LockFile(object): Release our lock if we have one """ if not self._has_lock(): - return - + return os.remove(self._lock_file_path()) self._owns_lock = False + class BlockingLockFile(LockFile): """The lock file will block until a lock could be obtained, or fail after a specified timeout""" @@ -206,7 +221,7 @@ class BlockingLockFile(LockFile): maxtime = starttime + float(self._max_block_time) while True: try: - self._obtain_lock_or_raise() + super(BlockingLockFile, self)._obtain_lock() except IOError: curtime = time.time() if curtime >= maxtime: @@ -219,7 +234,6 @@ class BlockingLockFile(LockFile): # END endless loop - class ConcurrentWriteOperation(LockFile): """ This class facilitates a safe write operation to a file on disk such that we: |