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# -*- test-case-name: twisted.test.test_adbapi -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
An asynchronous mapping to U{DB-API
2.0<http://www.python.org/topics/database/DatabaseAPI-2.0.html>}.
"""
from twisted.internet import threads
from twisted.python import log, reflect
class ConnectionLost(Exception):
"""
This exception means that a db connection has been lost. Client code may
try again.
"""
class Connection:
"""
A wrapper for a DB-API connection instance.
The wrapper passes almost everything to the wrapped connection and so has
the same API. However, the L{Connection} knows about its pool and also
handle reconnecting should when the real connection dies.
"""
def __init__(self, pool):
self._pool = pool
self._connection = None
self.reconnect()
def close(self):
# The way adbapi works right now means that closing a connection is
# a really bad thing as it leaves a dead connection associated with
# a thread in the thread pool.
# Really, I think closing a pooled connection should return it to the
# pool but that's handled by the runWithConnection method already so,
# rather than upsetting anyone by raising an exception, let's ignore
# the request
pass
def rollback(self):
if not self._pool.reconnect:
self._connection.rollback()
return
try:
self._connection.rollback()
curs = self._connection.cursor()
curs.execute(self._pool.good_sql)
curs.close()
self._connection.commit()
return
except BaseException:
log.err(None, "Rollback failed")
self._pool.disconnect(self._connection)
if self._pool.noisy:
log.msg("Connection lost.")
raise ConnectionLost()
def reconnect(self):
if self._connection is not None:
self._pool.disconnect(self._connection)
self._connection = self._pool.connect()
def __getattr__(self, name):
return getattr(self._connection, name)
class Transaction:
"""
A lightweight wrapper for a DB-API 'cursor' object.
Relays attribute access to the DB cursor. That is, you can call
C{execute()}, C{fetchall()}, etc., and they will be called on the
underlying DB-API cursor object. Attributes will also be retrieved from
there.
"""
_cursor = None
def __init__(self, pool, connection):
self._pool = pool
self._connection = connection
self.reopen()
def close(self):
_cursor = self._cursor
self._cursor = None
_cursor.close()
def reopen(self):
if self._cursor is not None:
self.close()
try:
self._cursor = self._connection.cursor()
return
except BaseException:
if not self._pool.reconnect:
raise
else:
log.err(None, "Cursor creation failed")
if self._pool.noisy:
log.msg("Connection lost, reconnecting")
self.reconnect()
self._cursor = self._connection.cursor()
def reconnect(self):
self._connection.reconnect()
self._cursor = None
def __getattr__(self, name):
return getattr(self._cursor, name)
class ConnectionPool:
"""
Represent a pool of connections to a DB-API 2.0 compliant database.
@ivar connectionFactory: factory for connections, default to L{Connection}.
@type connectionFactory: any callable.
@ivar transactionFactory: factory for transactions, default to
L{Transaction}.
@type transactionFactory: any callable
@ivar shutdownID: L{None} or a handle on the shutdown event trigger which
will be used to stop the connection pool workers when the reactor
stops.
@ivar _reactor: The reactor which will be used to schedule startup and
shutdown events.
@type _reactor: L{IReactorCore} provider
"""
CP_ARGS = "min max name noisy openfun reconnect good_sql".split()
noisy = False # If true, generate informational log messages
min = 3 # Minimum number of connections in pool
max = 5 # Maximum number of connections in pool
name = None # Name to assign to thread pool for debugging
openfun = None # A function to call on new connections
reconnect = False # Reconnect when connections fail
good_sql = "select 1" # A query which should always succeed
running = False # True when the pool is operating
connectionFactory = Connection
transactionFactory = Transaction
# Initialize this to None so it's available in close() even if start()
# never runs.
shutdownID = None
def __init__(self, dbapiName, *connargs, **connkw):
"""
Create a new L{ConnectionPool}.
Any positional or keyword arguments other than those documented here
are passed to the DB-API object when connecting. Use these arguments to
pass database names, usernames, passwords, etc.
@param dbapiName: an import string to use to obtain a DB-API compatible
module (e.g. C{'pyPgSQL.PgSQL'})
@keyword cp_min: the minimum number of connections in pool (default 3)
@keyword cp_max: the maximum number of connections in pool (default 5)
@keyword cp_noisy: generate informational log messages during operation
(default C{False})
@keyword cp_openfun: a callback invoked after every C{connect()} on the
underlying DB-API object. The callback is passed a new DB-API
connection object. This callback can setup per-connection state
such as charset, timezone, etc.
@keyword cp_reconnect: detect connections which have failed and reconnect
(default C{False}). Failed connections may result in
L{ConnectionLost} exceptions, which indicate the query may need to
be re-sent.
@keyword cp_good_sql: an sql query which should always succeed and change
no state (default C{'select 1'})
@keyword cp_reactor: use this reactor instead of the global reactor
(added in Twisted 10.2).
@type cp_reactor: L{IReactorCore} provider
"""
self.dbapiName = dbapiName
self.dbapi = reflect.namedModule(dbapiName)
if getattr(self.dbapi, "apilevel", None) != "2.0":
log.msg("DB API module not DB API 2.0 compliant.")
if getattr(self.dbapi, "threadsafety", 0) < 1:
log.msg("DB API module not sufficiently thread-safe.")
reactor = connkw.pop("cp_reactor", None)
if reactor is None:
from twisted.internet import reactor
self._reactor = reactor
self.connargs = connargs
self.connkw = connkw
for arg in self.CP_ARGS:
cpArg = f"cp_{arg}"
if cpArg in connkw:
setattr(self, arg, connkw[cpArg])
del connkw[cpArg]
self.min = min(self.min, self.max)
self.max = max(self.min, self.max)
# All connections, hashed on thread id
self.connections = {}
# These are optional so import them here
from twisted.python import threadable, threadpool
self.threadID = threadable.getThreadID
self.threadpool = threadpool.ThreadPool(self.min, self.max)
self.startID = self._reactor.callWhenRunning(self._start)
def _start(self):
self.startID = None
return self.start()
def start(self):
"""
Start the connection pool.
If you are using the reactor normally, this function does *not*
need to be called.
"""
if not self.running:
self.threadpool.start()
self.shutdownID = self._reactor.addSystemEventTrigger(
"during", "shutdown", self.finalClose
)
self.running = True
def runWithConnection(self, func, *args, **kw):
"""
Execute a function with a database connection and return the result.
@param func: A callable object of one argument which will be executed
in a thread with a connection from the pool. It will be passed as
its first argument a L{Connection} instance (whose interface is
mostly identical to that of a connection object for your DB-API
module of choice), and its results will be returned as a
L{Deferred}. If the method raises an exception the transaction will
be rolled back. Otherwise, the transaction will be committed.
B{Note} that this function is B{not} run in the main thread: it
must be threadsafe.
@param args: positional arguments to be passed to func
@param kw: keyword arguments to be passed to func
@return: a L{Deferred} which will fire the return value of
C{func(Transaction(...), *args, **kw)}, or a
L{twisted.python.failure.Failure}.
"""
return threads.deferToThreadPool(
self._reactor, self.threadpool, self._runWithConnection, func, *args, **kw
)
def _runWithConnection(self, func, *args, **kw):
conn = self.connectionFactory(self)
try:
result = func(conn, *args, **kw)
conn.commit()
return result
except BaseException:
try:
conn.rollback()
except BaseException:
log.err(None, "Rollback failed")
raise
def runInteraction(self, interaction, *args, **kw):
"""
Interact with the database and return the result.
The 'interaction' is a callable object which will be executed in a
thread using a pooled connection. It will be passed an L{Transaction}
object as an argument (whose interface is identical to that of the
database cursor for your DB-API module of choice), and its results will
be returned as a L{Deferred}. If running the method raises an
exception, the transaction will be rolled back. If the method returns a
value, the transaction will be committed.
NOTE that the function you pass is *not* run in the main thread: you
may have to worry about thread-safety in the function you pass to this
if it tries to use non-local objects.
@param interaction: a callable object whose first argument is an
L{adbapi.Transaction}.
@param args: additional positional arguments to be passed to
interaction
@param kw: keyword arguments to be passed to interaction
@return: a Deferred which will fire the return value of
C{interaction(Transaction(...), *args, **kw)}, or a
L{twisted.python.failure.Failure}.
"""
return threads.deferToThreadPool(
self._reactor,
self.threadpool,
self._runInteraction,
interaction,
*args,
**kw,
)
def runQuery(self, *args, **kw):
"""
Execute an SQL query and return the result.
A DB-API cursor which will be invoked with C{cursor.execute(*args,
**kw)}. The exact nature of the arguments will depend on the specific
flavor of DB-API being used, but the first argument in C{*args} be an
SQL statement. The result of a subsequent C{cursor.fetchall()} will be
fired to the L{Deferred} which is returned. If either the 'execute' or
'fetchall' methods raise an exception, the transaction will be rolled
back and a L{twisted.python.failure.Failure} returned.
The C{*args} and C{**kw} arguments will be passed to the DB-API
cursor's 'execute' method.
@return: a L{Deferred} which will fire the return value of a DB-API
cursor's 'fetchall' method, or a L{twisted.python.failure.Failure}.
"""
return self.runInteraction(self._runQuery, *args, **kw)
def runOperation(self, *args, **kw):
"""
Execute an SQL query and return L{None}.
A DB-API cursor which will be invoked with C{cursor.execute(*args,
**kw)}. The exact nature of the arguments will depend on the specific
flavor of DB-API being used, but the first argument in C{*args} will be
an SQL statement. This method will not attempt to fetch any results
from the query and is thus suitable for C{INSERT}, C{DELETE}, and other
SQL statements which do not return values. If the 'execute' method
raises an exception, the transaction will be rolled back and a
L{Failure} returned.
The C{*args} and C{*kw} arguments will be passed to the DB-API cursor's
'execute' method.
@return: a L{Deferred} which will fire with L{None} or a
L{twisted.python.failure.Failure}.
"""
return self.runInteraction(self._runOperation, *args, **kw)
def close(self):
"""
Close all pool connections and shutdown the pool.
"""
if self.shutdownID:
self._reactor.removeSystemEventTrigger(self.shutdownID)
self.shutdownID = None
if self.startID:
self._reactor.removeSystemEventTrigger(self.startID)
self.startID = None
self.finalClose()
def finalClose(self):
"""
This should only be called by the shutdown trigger.
"""
self.shutdownID = None
self.threadpool.stop()
self.running = False
for conn in self.connections.values():
self._close(conn)
self.connections.clear()
def connect(self):
"""
Return a database connection when one becomes available.
This method blocks and should be run in a thread from the internal
threadpool. Don't call this method directly from non-threaded code.
Using this method outside the external threadpool may exceed the
maximum number of connections in the pool.
@return: a database connection from the pool.
"""
tid = self.threadID()
conn = self.connections.get(tid)
if conn is None:
if self.noisy:
log.msg(f"adbapi connecting: {self.dbapiName}")
conn = self.dbapi.connect(*self.connargs, **self.connkw)
if self.openfun is not None:
self.openfun(conn)
self.connections[tid] = conn
return conn
def disconnect(self, conn):
"""
Disconnect a database connection associated with this pool.
Note: This function should only be used by the same thread which called
L{ConnectionPool.connect}. As with C{connect}, this function is not
used in normal non-threaded Twisted code.
"""
tid = self.threadID()
if conn is not self.connections.get(tid):
raise Exception("wrong connection for thread")
if conn is not None:
self._close(conn)
del self.connections[tid]
def _close(self, conn):
if self.noisy:
log.msg(f"adbapi closing: {self.dbapiName}")
try:
conn.close()
except BaseException:
log.err(None, "Connection close failed")
def _runInteraction(self, interaction, *args, **kw):
conn = self.connectionFactory(self)
trans = self.transactionFactory(self, conn)
try:
result = interaction(trans, *args, **kw)
trans.close()
conn.commit()
return result
except BaseException:
try:
conn.rollback()
except BaseException:
log.err(None, "Rollback failed")
raise
def _runQuery(self, trans, *args, **kw):
trans.execute(*args, **kw)
return trans.fetchall()
def _runOperation(self, trans, *args, **kw):
trans.execute(*args, **kw)
def __getstate__(self):
return {
"dbapiName": self.dbapiName,
"min": self.min,
"max": self.max,
"noisy": self.noisy,
"reconnect": self.reconnect,
"good_sql": self.good_sql,
"connargs": self.connargs,
"connkw": self.connkw,
}
def __setstate__(self, state):
self.__dict__ = state
self.__init__(self.dbapiName, *self.connargs, **self.connkw)
__all__ = ["Transaction", "ConnectionPool"]
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