pool.py :  » Project-Management » Trac » Trac-0.11.7 » trac » db » Python Open Source

Home
Python Open Source
1.3.1.2 Python
2.Ajax
3.Aspect Oriented
4.Blog
5.Build
6.Business Application
7.Chart Report
8.Content Management Systems
9.Cryptographic
10.Database
11.Development
12.Editor
13.Email
14.ERP
15.Game 2D 3D
16.GIS
17.GUI
18.IDE
19.Installer
20.IRC
21.Issue Tracker
22.Language Interface
23.Log
24.Math
25.Media Sound Audio
26.Mobile
27.Network
28.Parser
29.PDF
30.Project Management
31.RSS
32.Search
33.Security
34.Template Engines
35.Test
36.UML
37.USB Serial
38.Web Frameworks
39.Web Server
40.Web Services
41.Web Unit
42.Wiki
43.Windows
44.XML
Python Open Source » Project Management » Trac 
Trac » Trac 0.11.7 » trac » db » pool.py
# -*- coding: utf-8 -*-
#
# Copyright (C)2005-2009 Edgewall Software
# Copyright (C) 2005 Christopher Lenz <cmlenz@gmx.de>
# All rights reserved.
#
# This software is licensed as described in the file COPYING, which
# you should have received as part of this distribution. The terms
# are also available at http://trac.edgewall.org/wiki/TracLicense.
#
# This software consists of voluntary contributions made by many
# individuals. For the exact contribution history, see the revision
# history and logs, available at http://trac.edgewall.org/log/.
#
# Author: Christopher Lenz <cmlenz@gmx.de>

try:
    import threading
except ImportError:
    import dummy_threading as threading
    threading._get_ident = lambda: 0
import os
import time

from trac.db.util import ConnectionWrapper
from trac.util.translation import _


class TimeoutError(Exception):
    """Exception raised by the connection pool when no connection has become
    available after a given timeout."""


class PooledConnection(ConnectionWrapper):
    """A database connection that can be pooled. When closed, it gets returned
    to the pool.
    """

    def __init__(self, pool, cnx, key, tid, log=None):
        ConnectionWrapper.__init__(self, cnx, log)
        self._pool = pool
        self._key = key
        self._tid = tid

    def close(self):
        if self.cnx:
            self._pool._return_cnx(self.cnx, self._key, self._tid)
            self.cnx = None
            self.log = None

    def __del__(self):
        self.close()


def try_rollback(cnx):
    """Resets the Connection in a safe way, returning True when it succeeds.
    
    The rollback we do for safety on a Connection can fail at
    critical times because of a timeout on the Connection.
    """
    try:
        cnx.rollback() # resets the connection
        return True
    except Exception:
        cnx.close()
        return False


class ConnectionPoolBackend(object):
    """A process-wide LRU-based connection pool.
    """
    def __init__(self, maxsize):
        self._available = threading.Condition(threading.RLock())
        self._maxsize = maxsize
        self._active = {}
        self._pool = []
        self._pool_key = []
        self._pool_time = []

    def get_cnx(self, connector, kwargs, timeout=None):
        num = 1
        cnx = None
        log = kwargs.get('log')
        key = unicode(kwargs)
        start = time.time()
        tid = threading._get_ident()
        self._available.acquire()
        try:
            while True:
                # First choice: Return the same cnx already used by the thread
                if (tid, key) in self._active:
                    cnx, num = self._active[(tid, key)]
                    num += 1
                # Second best option: Reuse a live pooled connection
                elif key in self._pool_key:
                    idx = self._pool_key.index(key)
                    self._pool_key.pop(idx)
                    self._pool_time.pop(idx)
                    cnx = self._pool.pop(idx)
                    # If possible, verify that the pooled connection is
                    # still available and working.
                    if hasattr(cnx, 'ping'):
                        try:
                            cnx.ping()
                        except:
                            continue
                # Third best option: Create a new connection
                elif len(self._active) + len(self._pool) < self._maxsize:
                    cnx = connector.get_connection(**kwargs)
                # Forth best option: Replace a pooled connection with a new one
                elif len(self._active)  < self._maxsize:
                    # Remove the LRU connection in the pool
                    self._pool.pop(0).close()
                    self._pool_key.pop(0)
                    self._pool_time.pop(0)
                    cnx = connector.get_connection(**kwargs)
                if cnx:
                    self._active[(tid, key)] = (cnx, num)
                    return PooledConnection(self, cnx, key, tid, log)
                # Worst option: wait until a connection pool slot is available
                if timeout and (time.time() - start) > timeout:
                    raise TimeoutError(_('Unable to get database '
                                         'connection within %(time)d '
                                         'seconds', time=timeout))
                elif timeout:
                    self._available.wait(timeout)
                else:
                    self._available.wait()
        finally:
            self._available.release()

    def _return_cnx(self, cnx, key, tid):
        self._available.acquire()
        try:
            assert (tid, key) in self._active
            cnx, num = self._active[(tid, key)]
            if num == 1:
                del self._active[(tid, key)]
                self._available.notify() 
                if cnx.poolable and try_rollback(cnx):
                    self._pool.append(cnx)
                    self._pool_key.append(key)
                    self._pool_time.append(time.time())
            else:
                self._active[(tid, key)] = (cnx, num - 1)
        finally:
            self._available.release()

    def shutdown(self, tid=None):
        """Close pooled connections not used in a while"""
        delay = 120
        if tid is None:
            delay = 0
        when = time.time() - delay
        self._available.acquire()
        try:
            while self._pool_time and self._pool_time[0] <= when:
                self._pool.pop(0)
                self._pool_key.pop(0)
                self._pool_time.pop(0)
        finally:
            self._available.release()


_pool_size = int(os.environ.get('TRAC_DB_POOL_SIZE', 10))
_backend = ConnectionPoolBackend(_pool_size)


class ConnectionPool(object):
    def __init__(self, maxsize, connector, **kwargs):
        # maxsize not used right now but kept for api compatibility
        self._connector = connector
        self._kwargs = kwargs

    def get_cnx(self, timeout=None):
        return _backend.get_cnx(self._connector, self._kwargs, timeout)

    def shutdown(self, tid=None):
        _backend.shutdown(tid)

www.java2java.com | Contact Us
Copyright 2009 - 12 Demo Source and Support. All rights reserved.
All other trademarks are property of their respective owners.