def _Acquire(self, lease_time):
self.lock_token = thread.get_ident()
sqlite_connection = self.store.cache.Get(self.subject)
# We first check if there is a lock on the subject.
# Next we set our lease time and lock_token as identification.
with sqlite_connection:
locked_until, stored_token = sqlite_connection.GetLock(
self.subject)
# This is currently locked by another thread.
if locked_until and (time.time() * 1e6) < float(locked_until):
raise data_store.DBSubjectLockError("Subject %s is locked" %
self.subject)
# Subject is not locked, we take a lease on it.
self.expires = int((time.time() + lease_time) * 1e6)
sqlite_connection.SetLock(self.subject, self.expires,
self.lock_token)
# TODO(user): This shouldn't really be necessary, and seems fragile. We
# should be able to use an UPDATE WHERE lock_expiration < now inside a
# transaction and check that we changed one row.
# Check if the lock stuck. If the stored token is not ours
# then probably someone was able to grab it before us.
locked_until, stored_token = sqlite_connection.GetLock(self.subject)
if stored_token != self.lock_token:
raise data_store.DBSubjectLockError("Unable to lock subject %s" %
self.subject)
self.locked = True
def _Acquire(self, lease_time):
self.lock_token = thread.get_ident()
self.expires = int((time.time() + lease_time) * 1e6)
# This single query will create a new entry if one doesn't exist, and update
# the lock value if there is a lock but it's expired. The SELECT 1
# statement checks if there is a current lock. The select from dual is
# essentially a way to get the numbers into the query conditional on there
# not being an existing lock.
query = (
"REPLACE INTO locks(lock_expiration, lock_owner, subject_hash) "
"SELECT %s, %s, unhex(md5(%s)) FROM dual WHERE NOT EXISTS (SELECT 1 "
"FROM locks WHERE subject_hash=unhex(md5(%s)) AND (lock_expiration > "
"%s))")
args = [
self.expires, self.lock_token, self.subject, self.subject,
time.time() * 1e6
]
unused_results, rowcount = self.store.ExecuteQuery(query, args)
# New row rowcount == 1, updating expired lock rowcount == 2.
if rowcount == 0:
raise data_store.DBSubjectLockError("Subject %s is locked" %
self.subject)
self.locked = True
def _Acquire(self, lease_time):
self.expires = int((time.time() + lease_time) * 1e6)
with self.store.lock:
expires = self.store.transactions.get(self.subject)
if expires and (time.time() * 1e6) < expires:
raise data_store.DBSubjectLockError("Subject is locked")
self.store.transactions[self.subject] = self.expires
self.locked = True
