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adbapi.py
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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"]