Source code for django_mysql.locks

from collections import OrderedDict

from django.db import connections
from django.db.transaction import TransactionManagementError, atomic
from django.db.utils import DEFAULT_DB_ALIAS

from django_mysql.exceptions import TimeoutError


[docs]class Lock(object): def __init__(self, name, acquire_timeout=10.0, using=None): self.acquire_timeout = acquire_timeout if using is None: self.db = DEFAULT_DB_ALIAS else: self.db = using # For multi-database servers, we prefix the name of the lock wth # the database, to protect against concurrent apps with the same locks self.name = self.make_name(self.db, name) @classmethod def make_name(cls, db, name): return ".".join((connections[db].settings_dict["NAME"], name)) @classmethod def unmake_name(cls, db, name): # Cut off the 'dbname.' prefix db_name = connections[db].settings_dict["NAME"] return name[len(db_name) + 1 :] def get_cursor(self): return connections[self.db].cursor() def __enter__(self): return self.acquire() def __exit__(self, exc_type, exc_value, traceback): self.release()
[docs] def acquire(self): with self.get_cursor() as cursor: cursor.execute("SELECT GET_LOCK(%s, %s)", (self.name, self.acquire_timeout)) result = cursor.fetchone()[0] if result == 1: return self else: raise TimeoutError( "Waited >{} seconds to gain lock".format(self.acquire_timeout) )
[docs] def release(self): with self.get_cursor() as cursor: cursor.execute("SELECT RELEASE_LOCK(%s)", (self.name,)) result = cursor.fetchone()[0] if result is None or result == 0: raise ValueError("Tried to release an unheld lock.")
[docs] def is_held(self): return self.holding_connection_id() is not None
[docs] def holding_connection_id(self): with self.get_cursor() as cursor: cursor.execute("SELECT IS_USED_LOCK(%s)", (self.name,)) return cursor.fetchone()[0]
[docs] @classmethod def held_with_prefix(cls, prefix, using=DEFAULT_DB_ALIAS): # Use the METADATA_LOCK_INFO table from the MariaDB plugin to show # which locks of a given prefix are held prefix = cls.make_name(using, prefix) with connections[using].cursor() as cursor: cursor.execute( """SELECT TABLE_SCHEMA, THREAD_ID FROM INFORMATION_SCHEMA.METADATA_LOCK_INFO WHERE TABLE_SCHEMA LIKE %s AND LOCK_TYPE = 'User Lock'""", (prefix + "%",), ) return {cls.unmake_name(using, row[0]): row[1] for row in cursor.fetchall()}
[docs]class TableLock(object): def __init__(self, read=None, write=None, using=None): self.read = self._process_names(read) self.write = self._process_names(write) self.db = DEFAULT_DB_ALIAS if using is None else using def _process_names(self, names): """ Convert a list of models/table names into a list of table names. Deals with cases of model inheritance, etc. """ if names is None: return [] table_names = OrderedDict() # Preserve order and ignore duplicates while len(names): name = names.pop(0) if hasattr(name, "_meta"): if name._meta.abstract: raise ValueError( "Can't lock abstract model {}".format(name.__name__) ) table_names[name._meta.db_table] = True # Include all parent models - the keys are the model classes if name._meta.parents: names.extend(name._meta.parents.keys()) else: table_names[name] = True return table_names.keys() def __enter__(self): return self.acquire() def __exit__(self, exc_type, exc_value, traceback): self.release(exc_type, exc_value, traceback)
[docs] def acquire(self): connection = connections[self.db] qn = connection.ops.quote_name with connection.cursor() as cursor: if not connection.get_autocommit(): raise TransactionManagementError( "InnoDB requires that we not be in a transaction when " "gaining a table lock." ) # Begin transaction - does 'SET autocommit = 0' self._atomic = atomic(using=self.db) self._atomic.__enter__() locks = [] for name in self.read: locks.append("{} READ".format(qn(name))) for name in self.write: locks.append("{} WRITE".format(qn(name))) cursor.execute("LOCK TABLES {}".format(", ".join(locks)))
[docs] def release(self, exc_type=None, exc_value=None, traceback=None): connection = connections[self.db] with connection.cursor() as cursor: self._atomic.__exit__(exc_type, exc_value, traceback) self._atomic = None cursor.execute("UNLOCK TABLES")