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#
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# Copyright (C) 2020-2021 Georg Richter and MariaDB Corporation AB
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# This library is free software; you can redistribute it and/or
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# modify it under the terms of the GNU Library General Public
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# License as published by the Free Software Foundation; either
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# version 2 of the License, or (at your option) any later version.
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# This library is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Library General Public License for more details.
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# You should have received a copy of the GNU Library General Public
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# License along with this library; if not see <http://www.gnu.org/licenses>
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# or write to the Free Software Foundation, Inc.,
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# 51 Franklin St., Fifth Floor, Boston, MA 02110, USA
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#
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import mariadb
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import _thread
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import time
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from mariadb.constants import STATUS
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MAX_POOL_SIZE = 64
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class ConnectionPool(object):
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"""
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Class defining a pool of database connections
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MariaDB Connector/Python supports simple connection pooling.
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A connection pool holds a number of open connections and handles thread safety when providing connections to threads.
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The size of a connection pool is configurable at creation time, but cannot be changed afterward. The maximum size of a connection pool is limited to 64 connections.
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Keyword Arguments:
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- **`pool_name`** (``str``) - Name of connection pool
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- **`pool_size`** (``int``) - Size of pool. The Maximum allowed number is 64. Default to 5
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- **`pool_reset_connection`** (``bool``) - Will reset the connection before returning it to the pool. Default to True.
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- **`pool_validation_interval`** (``int``) - Specifies the validation interval in milliseconds after which the status of a connection requested from the pool is checked. A value of 0 means that the status will always be checked. Default to 500 (Added in version 1.1.6)
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- **\*\*kwargs** - Optional additional connection arguments, as described in mariadb.connect() method.
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"""
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def __init__(self, *args, **kwargs):
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"""
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Creates a connection pool class
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:param str pool_name:
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Name of connection pool
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:param int pool_size:
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Size of pool. If not specified, the default value of 5 will be used.
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The Maximum allowed number is 64.
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:param bool pool_reset_connection:
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Will reset the connection before returning it to the pool.
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The Default value is True.
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:param **kwargs kwargs:
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Optional additional connection arguments, as described in
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mariadb.connect() method.
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"""
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self._connections_free = []
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self._connections_used = []
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self._pool_args = {}
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self._conn_args = {}
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self._lock_pool = _thread.RLock()
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self.__closed = 0
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key_words = ["pool_name", "pool_size", "pool_reset_connection",
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"pool_validation_interval"]
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# check if pool_name was provided
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if kwargs and "pool_name" in kwargs:
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# check if pool_name already exists
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if kwargs["pool_name"] in mariadb._CONNECTION_POOLS:
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raise mariadb.ProgrammingError("Pool '%s' already exists"
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% kwargs["pool_name"])
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else:
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raise mariadb.ProgrammingError("No pool name specified")
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# save pool keyword arguments
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self._pool_args["name"] = kwargs.get("pool_name")
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self._pool_args["size"] = int(kwargs.get("pool_size", 5))
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self._pool_args["reset_connection"] = \
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bool(kwargs.get("pool_reset_connection", True))
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self._pool_args["validation_interval"] = \
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int(kwargs.get("pool_validation_interval", 500))
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# validate pool size (must be in range between 1 and MAX_POOL_SIZE)
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if not (0 < self._pool_args["size"] <= MAX_POOL_SIZE):
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raise mariadb.ProgrammingError("Pool size must be in range of "
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"1 and %s" % MAX_POOL_SIZE)
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# store pool and connection arguments
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self._conn_args = kwargs.copy()
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for key in key_words:
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if key in self._conn_args:
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del self._conn_args[key]
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if len(self._conn_args) > 0:
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with self._lock_pool:
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# fill connection pool
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for i in range(0, self._pool_args["size"]):
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try:
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connection = mariadb.Connection(**self._conn_args)
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except mariadb.Error:
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# if an error occurred, close all connections
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# and raise exception
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for j in reversed(range(0, len(self._connections_free))):
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try:
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self._connections_free[j].close()
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except mariadb.Error:
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# connect failed, so we are not
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# interested in errors
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# from close() method
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pass
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del self._connections_free[j]
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raise
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self.add_connection(connection)
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# store connection pool in _CONNECTION_POOLS
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mariadb._CONNECTION_POOLS[self._pool_args["name"]] = self
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def _replace_connection(self, connection):
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"""
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Removes the given connection and adds a new connection.
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"""
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if connection:
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if connection in self._connections_free:
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x = self._connections_free.index(connection)
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del self._connections_free[x]
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elif connection in self._connections_used:
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x = self._connections_used.index(connection)
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del self._connections_used[x]
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connection._Connection__pool = None
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connection.close()
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return self.add_connection()
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def __repr__(self):
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if (self.__closed):
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return "<mariadb.connectionPool.ConnectionPool object (closed) "\
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"at %s>" % (hex(id(self)),)
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else:
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return "<mariadb.connectionPool.ConnectionPool object (name=%s) "\
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"at %s>" % (self.pool_name, hex(id(self)))
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def add_connection(self, connection=None):
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"""
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Adds a connection object to the connection pool.
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In case that the pool doesn’t have a free slot or is not configured,
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a PoolError exception will be raised.
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"""
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if not self._conn_args:
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raise mariadb.PoolError("Couldn't get configuration for pool %s" %
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self._pool_args["name"])
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if (connection is not None and
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not isinstance(connection, mariadb.connections.Connection)):
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raise mariadb.ProgrammingError("Passed parameter is not a "
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"connection object")
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if connection is None and len(self._conn_args) == 0:
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raise mariadb.PoolError("Can't get configuration for pool %s" %
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self._pool_args["name"])
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total = len(self._connections_free + self._connections_used)
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if total >= self._pool_args["size"]:
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raise mariadb.PoolError("Can't add connection to pool %s: "
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"No free slot available (%s)." %
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(self._pool_args["name"],
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total))
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with self._lock_pool:
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if connection is None:
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connection = mariadb.Connection(**self._conn_args)
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connection._Connection__pool = self
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connection.__last_used = time.perf_counter_ns()
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self._connections_free.append(connection)
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return connection
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def get_connection(self):
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"""
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Returns a connection from the connection pool or raises a PoolError
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exception if a connection is not available.
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"""
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conn = None
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with self._lock_pool:
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for i in range(0, len(self._connections_free)):
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conn = self._connections_free[i]
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dt = (time.perf_counter_ns() - conn.__last_used) / 1000000
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if dt > self._pool_args["validation_interval"]:
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try:
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conn.ping()
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except mariadb.Error:
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conn = self._replace_connection(conn)
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if not conn:
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continue
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conn._used += 1
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self._connections_used.append(conn)
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idx = self._connections_free.index(conn)
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del self._connections_free[idx]
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return conn
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raise mariadb.PoolError("No connection available")
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def _close_connection(self, connection):
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"""
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Returns connection to the pool. Internally used
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by connection object.
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"""
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with self._lock_pool:
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try:
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if self._pool_args["reset_connection"]:
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connection.reset()
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elif connection.server_status & STATUS.IN_TRANS:
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connection.rollback()
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except mariadb.Error:
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self._replace_connection(connection)
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if connection:
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if connection in self._connections_used:
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x = self._connections_used.index(connection)
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del self._connections_used[x]
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connection.__last_used = time.perf_counter_ns()
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self._connections_free.append(connection)
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def set_config(self, **kwargs):
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"""
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Sets the connection configuration for the connection pool.
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For valid connection arguments, check the mariadb.connect() method.
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Note: This method doesn't create connections in the pool.
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To fill the pool, one has to use add_connection() ḿethod.
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"""
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self._conn_args = kwargs
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def close(self):
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"""Closes connection pool and all connections."""
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try:
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for c in (self._connections_free + self._connections_used):
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c._Connection__pool = None
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c.close()
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finally:
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self._connections_free = None
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self._connections_used = None
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del mariadb._CONNECTION_POOLS[self._pool_args["name"]]
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@property
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def pool_name(self):
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"""Returns the name of the connection pool."""
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return self._pool_args["name"]
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@property
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def pool_size(self):
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"""Returns the size of the connection pool."""
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return self._pool_args["size"]
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@property
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def max_size(self):
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"Returns the maximum size for connection pools."""
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return MAX_POOL_SIZE
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@property
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def connection_count(self):
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"Returns the number of connections in connection pool."""
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try:
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return len(self._connections_free + self._connections_used)
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except Exception:
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return 0
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@property
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def pool_reset_connection(self):
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"""
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If set to true, the connection will be reset on both client and server
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side after .close() method was called
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"""
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return self._pool_args["reset_connection"]
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@pool_reset_connection.setter
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def pool_reset_connection(self, reset):
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self._pool_args["reset_connection"] = reset
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