# sqlalchemy/pool.py
# Copyright (C) 2005-2018 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php


"""Connection pooling for DB-API connections.

Provides a number of connection pool implementations for a variety of
usage scenarios and thread behavior requirements imposed by the
application, DB-API or database itself.

Also provides a DB-API 2.0 connection proxying mechanism allowing
regular DB-API connect() methods to be transparently managed by a
SQLAlchemy connection pool.
"""

import time
import traceback
import weakref

from . import exc, log, event, interfaces, util
from .util import queue as sqla_queue
from .util import threading, memoized_property, \
    chop_traceback

from collections import deque
proxies = {}


def manage(module, **params):
    r"""Return a proxy for a DB-API module that automatically
    pools connections.

    Given a DB-API 2.0 module and pool management parameters, returns
    a proxy for the module that will automatically pool connections,
    creating new connection pools for each distinct set of connection
    arguments sent to the decorated module's connect() function.

    :param module: a DB-API 2.0 database module

    :param poolclass: the class used by the pool module to provide
      pooling.  Defaults to :class:`.QueuePool`.

    :param \**params: will be passed through to *poolclass*

    """
    try:
        return proxies[module]
    except KeyError:
        return proxies.setdefault(module, _DBProxy(module, **params))


def clear_managers():
    """Remove all current DB-API 2.0 managers.

    All pools and connections are disposed.
    """

    for manager in proxies.values():
        manager.close()
    proxies.clear()

reset_rollback = util.symbol('reset_rollback')
reset_commit = util.symbol('reset_commit')
reset_none = util.symbol('reset_none')


class _ConnDialect(object):

    """partial implementation of :class:`.Dialect`
    which provides DBAPI connection methods.

    When a :class:`.Pool` is combined with an :class:`.Engine`,
    the :class:`.Engine` replaces this with its own
    :class:`.Dialect`.

    """

    def do_rollback(self, dbapi_connection):
        dbapi_connection.rollback()

    def do_commit(self, dbapi_connection):
        dbapi_connection.commit()

    def do_close(self, dbapi_connection):
        dbapi_connection.close()

    def do_ping(self, dbapi_connection):
        raise NotImplementedError(
            "The ping feature requires that a dialect is "
            "passed to the connection pool.")


class Pool(log.Identified):

    """Abstract base class for connection pools."""

    _dialect = _ConnDialect()

    def __init__(self,
                 creator, recycle=-1, echo=None,
                 use_threadlocal=False,
                 logging_name=None,
                 reset_on_return=True,
                 listeners=None,
                 events=None,
                 dialect=None,
                 pre_ping=False,
                 _dispatch=None):
        """
        Construct a Pool.

        :param creator: a callable function that returns a DB-API
          connection object.  The function will be called with
          parameters.

        :param recycle: If set to non -1, number of seconds between
          connection recycling, which means upon checkout, if this
          timeout is surpassed the connection will be closed and
          replaced with a newly opened connection. Defaults to -1.

        :param logging_name:  String identifier which will be used within
          the "name" field of logging records generated within the
          "sqlalchemy.pool" logger. Defaults to a hexstring of the object's
          id.

        :param echo: If True, connections being pulled and retrieved
          from the pool will be logged to the standard output, as well
          as pool sizing information.  Echoing can also be achieved by
          enabling logging for the "sqlalchemy.pool"
          namespace. Defaults to False.

        :param use_threadlocal: If set to True, repeated calls to
          :meth:`connect` within the same application thread will be
          guaranteed to return the same connection object, if one has
          already been retrieved from the pool and has not been
          returned yet.  Offers a slight performance advantage at the
          cost of individual transactions by default.  The
          :meth:`.Pool.unique_connection` method is provided to return
          a consistently unique connection to bypass this behavior
          when the flag is set.

          .. warning::  The :paramref:`.Pool.use_threadlocal` flag
             **does not affect the behavior** of :meth:`.Engine.connect`.
             :meth:`.Engine.connect` makes use of the
             :meth:`.Pool.unique_connection` method which **does not use thread
             local context**.  To produce a :class:`.Connection` which refers
             to the :meth:`.Pool.connect` method, use
             :meth:`.Engine.contextual_connect`.

             Note that other SQLAlchemy connectivity systems such as
             :meth:`.Engine.execute` as well as the orm
             :class:`.Session` make use of
             :meth:`.Engine.contextual_connect` internally, so these functions
             are compatible with the :paramref:`.Pool.use_threadlocal` setting.

          .. seealso::

            :ref:`threadlocal_strategy` - contains detail on the
            "threadlocal" engine strategy, which provides a more comprehensive
            approach to "threadlocal" connectivity for the specific
            use case of using :class:`.Engine` and :class:`.Connection` objects
            directly.

        :param reset_on_return: Determine steps to take on
          connections as they are returned to the pool.
          reset_on_return can have any of these values:

          * ``"rollback"`` - call rollback() on the connection,
            to release locks and transaction resources.
            This is the default value.  The vast majority
            of use cases should leave this value set.
          * ``True`` - same as 'rollback', this is here for
            backwards compatibility.
          * ``"commit"`` - call commit() on the connection,
            to release locks and transaction resources.
            A commit here may be desirable for databases that
            cache query plans if a commit is emitted,
            such as Microsoft SQL Server.  However, this
            value is more dangerous than 'rollback' because
            any data changes present on the transaction
            are committed unconditionally.
          * ``None`` - don't do anything on the connection.
            This setting should only be made on a database
            that has no transaction support at all,
            namely MySQL MyISAM.   By not doing anything,
            performance can be improved.   This
            setting should **never be selected** for a
            database that supports transactions,
            as it will lead to deadlocks and stale
            state.
          * ``"none"`` - same as ``None``

            .. versionadded:: 0.9.10

          * ``False`` - same as None, this is here for
            backwards compatibility.

          .. versionchanged:: 0.7.6
              :paramref:`.Pool.reset_on_return` accepts ``"rollback"``
              and ``"commit"`` arguments.

        :param events: a list of 2-tuples, each of the form
         ``(callable, target)`` which will be passed to :func:`.event.listen`
         upon construction.   Provided here so that event listeners
         can be assigned via :func:`.create_engine` before dialect-level
         listeners are applied.

        :param listeners: Deprecated.  A list of
          :class:`~sqlalchemy.interfaces.PoolListener`-like objects or
          dictionaries of callables that receive events when DB-API
          connections are created, checked out and checked in to the
          pool.  This has been superseded by
          :func:`~sqlalchemy.event.listen`.

        :param dialect: a :class:`.Dialect` that will handle the job
         of calling rollback(), close(), or commit() on DBAPI connections.
         If omitted, a built-in "stub" dialect is used.   Applications that
         make use of :func:`~.create_engine` should not use this parameter
         as it is handled by the engine creation strategy.

         .. versionadded:: 1.1 - ``dialect`` is now a public parameter
            to the :class:`.Pool`.

        :param pre_ping: if True, the pool will emit a "ping" (typically
         "SELECT 1", but is dialect-specific) on the connection
         upon checkout, to test if the connection is alive or not.   If not,
         the connection is transparently re-connected and upon success, all
         other pooled connections established prior to that timestamp are
         invalidated.     Requires that a dialect is passed as well to
         interpret the disconnection error.

         .. versionadded:: 1.2

        """
        if logging_name:
            self.logging_name = self._orig_logging_name = logging_name
        else:
            self._orig_logging_name = None

        log.instance_logger(self, echoflag=echo)
        self._threadconns = threading.local()
        self._creator = creator
        self._recycle = recycle
        self._invalidate_time = 0
        self._use_threadlocal = use_threadlocal
        self._pre_ping = pre_ping
        if reset_on_return in ('rollback', True, reset_rollback):
            self._reset_on_return = reset_rollback
        elif reset_on_return in ('none', None, False, reset_none):
            self._reset_on_return = reset_none
        elif reset_on_return in ('commit', reset_commit):
            self._reset_on_return = reset_commit
        else:
            raise exc.ArgumentError(
                "Invalid value for 'reset_on_return': %r"
                % reset_on_return)

        self.echo = echo

        if _dispatch:
            self.dispatch._update(_dispatch, only_propagate=False)
        if dialect:
            self._dialect = dialect
        if events:
            for fn, target in events:
                event.listen(self, target, fn)
        if listeners:
            util.warn_deprecated(
                "The 'listeners' argument to Pool (and "
                "create_engine()) is deprecated.  Use event.listen().")
            for l in listeners:
                self.add_listener(l)

    @property
    def _creator(self):
        return self.__dict__['_creator']

    @_creator.setter
    def _creator(self, creator):
        self.__dict__['_creator'] = creator
        self._invoke_creator = self._should_wrap_creator(creator)

    def _should_wrap_creator(self, creator):
        """Detect if creator accepts a single argument, or is sent
        as a legacy style no-arg function.

        """

        try:
            argspec = util.get_callable_argspec(self._creator, no_self=True)
        except TypeError:
            return lambda crec: creator()

        defaulted = argspec[3] is not None and len(argspec[3]) or 0
        positionals = len(argspec[0]) - defaulted

        # look for the exact arg signature that DefaultStrategy
        # sends us
        if (argspec[0], argspec[3]) == (['connection_record'], (None,)):
            return creator
        # or just a single positional
        elif positionals == 1:
            return creator
        # all other cases, just wrap and assume legacy "creator" callable
        # thing
        else:
            return lambda crec: creator()

    def _close_connection(self, connection):
        self.logger.debug("Closing connection %r", connection)

        try:
            self._dialect.do_close(connection)
        except Exception:
            self.logger.error("Exception closing connection %r",
                              connection, exc_info=True)

    @util.deprecated(
        2.7, "Pool.add_listener is deprecated.  Use event.listen()")
    def add_listener(self, listener):
        """Add a :class:`.PoolListener`-like object to this pool.

        ``listener`` may be an object that implements some or all of
        PoolListener, or a dictionary of callables containing implementations
        of some or all of the named methods in PoolListener.

        """
        interfaces.PoolListener._adapt_listener(self, listener)

    def unique_connection(self):
        """Produce a DBAPI connection that is not referenced by any
        thread-local context.

        This method is equivalent to :meth:`.Pool.connect` when the
        :paramref:`.Pool.use_threadlocal` flag is not set to True.
        When :paramref:`.Pool.use_threadlocal` is True, the
        :meth:`.Pool.unique_connection` method provides a means of bypassing
        the threadlocal context.

        """
        return _ConnectionFairy._checkout(self)