[Sqlalchemy-tickets] Issue #3043: Error "File descriptor was closed in another greenlet" using v0.9.4 and gevent.monkey.patch_all (zzzeek/sqlalchemy)

[Gaofeng L. <iss...@bi...>]

New issue 3043: Error "File descriptor was closed in another greenlet" using v0.9.4 and gevent.monkey.patch_all
https://bitbucket.org/zzzeek/sqlalchemy/issue/3043/error-file-descriptor-was-closed-in

Gaofeng Liang:

I'm using gevent and sqlalchemy in my thrift(RPC) project. I upgraded SQLAlchemy from v0.9.3 to v0.9.4 a few days ago and then found the error.
Following is how I use sqlalchemy and gevent:
* scoped_session(thread-local)
* use gevent.spawn to handle every request and session.close after finishing handling

The error is gone when SQLAlchemy is  downgraded to v0.9.3.

I noticed that the version 0.9.4 has "Key fixes include an enhancement to the mechanics of connection pool recycling to be more efficient ".  Does it have anything to do with the error.


```
#!python
File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py", line 233, in __get__
    return self.impl.get(instance_state(instance), dict_)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/orm/attributes.py", line 577, in get
    value = callable_(state, passive)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/orm/state.py", line 360, in __call__
    self.manager.deferred_scalar_loader(self, toload)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/orm/loading.py", line 606, in load_scalar_attributes
    
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/orm/loading.py", line 230, in load_on_ident
    return q.one()
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2361, in one
    raise orm_exc.NoResultFound("No row was found for one()")
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2404, in __iter__
    conn = conn.execution_options(**self._execution_options)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2419, in _execute_and_instances
    returned by this :class:`.Query`.
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 720, in execute
    """Execute a sql.FunctionElement object."""
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/sql/elements.py", line 317, in _execute_on_connection
    return connection._execute_clauseelement(self, multiparams, params)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 817, in _execute_clauseelement
    self.dispatch.after_execute(self,
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 947, in _execute_context
    context._fetch_implicit_returning(result)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1108, in _handle_dbapi_exception
    The operations inside the function are all invoked within the
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/util/compat.py", line 185, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 940, in _execute_context
    context.post_insert()
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/sqlalchemy/engine/default.py", line 435, in do_execute
    # after the initial set of 'isolation_level', if any, so is
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/pymysql/cursors.py", line 132, in execute
    result = self._query(query)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/pymysql/cursors.py", line 271, in _query
    conn.query(q)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/pymysql/connections.py", line 726, in query
    self._affected_rows = self._read_query_result(unbuffered=unbuffered)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/pymysql/connections.py", line 861, in _read_query_result
    result.read()
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/pymysql/connections.py", line 1064, in read
    first_packet = self.connection._read_packet()
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/pymysql/connections.py", line 825, in _read_packet
    packet = packet_type(self)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/pymysql/connections.py", line 242, in __init__
    self._recv_packet(connection)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/pymysql/connections.py", line 248, in _recv_packet
    packet_header = connection._read_bytes(4)
  File "/srv/virtualenvs/zeus2env/local/lib/python2.7/site-packages/pymysql/connections.py", line 838, in _read_bytes
    2013, "Lost connection to MySQL server during query (%r)" % (e,))
OperationalError: (OperationalError) (2013, "Lost connection to MySQL server during query (error(9, 'File descriptor was closed in another greenlet'))")



```

Responsible: zzzeek