如何在Flask微框架中使用Neo4j-embedded for Python(线程)？

我正在关注Flask教程(Flaskr),以便尝试使用Neo4j-embedded for Python.这是一个虚拟的.这是我的"主要"应用代码:

import os
import jpype
from neo4j import GraphDatabase
from flask import Flask, request, session, g, redirect, url_for, abort, render_template, flash

app = Flask(__name__)
app.config.from_pyfile(os.environ['APP_SETTINGS'])


def connectDB(): 
    return GraphDatabase(app.config['DATABASE'])


def initDB():
    db = connectDB()

    with db.transaction:
        users = db.node()
        roles = db.node()

        db.reference_node.USERS(users)
        db.reference_node.ROLES(roles)

        userIndex = db.node.indexes.create('users')

        user = db.node(name=app.config['ADMIN'])
        user.INSTANCE_OF(users)
        userIndex['name'][app.config['ADMIN']] = user

        role = db.node(type='superadmin')
        role.INSTANCE_OF(roles)

        role.ASSIGN_TO(user)

    db.shutdown()

    print "Database initialized."


def testDB():
    db = connectDB()

    with db.transaction:
        userIndex = db.node.indexes.get('users')
        user = userIndex['name'][app.config['ADMIN']].single
        username = user['name']

    db.shutdown()

    print "Admin username is '%s'. Database exists." % username


@app.before_request
def before_request():
    jpype.attachThreadToJVM()
    g.db = connectDB()


@app.teardown_request
def teardown_request(exception):
    g.db.shutdown()


@app.route('/')
def index():

    with g.db.transaction:
        userIndex = g.db.node.indexes.get('users')
        user = userIndex['name'][app.config['ADMIN']].single
        username = user['name']

    fields = dict(username=username)
    return render_template('index.html', fields=fields)


if os.path.exists(app.config['DATABASE']) == False:
    initDB()
else:
    testDB()

initDB()和testDB()工作得很好 - 没有Gremlin,PyLucene等 - 只是jpype和neo4j-embedded.最初,当我请求index()时,JVM将失败并且应用程序将终止.我在网上搜索了解我需要将"jpype.attachThreadToJVM()"行添加到before_request()中以解决python线程化JVM并且应用程序未终止的问题.但是,这会立即导致另一个问题:

Traceback (most recent call last):
  File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1518, in __call__
    return self.wsgi_app(environ, start_response)
  File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1506, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1504, in wsgi_app
    response = self.full_dispatch_request()
  File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1264, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1262, in full_dispatch_request
    rv = self.dispatch_request()
  File "/ht/dev/envFlask/lib/python2.7/site-packages/flask/app.py", line 1248, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/ht/dev/apps/evobox/evobox/__init__.py", line 68, in index
    userIndex = g.db.node.indexes.get('users')
  File "/ht/dev/envFlask/lib/python2.7/site-packages/neo4j/index.py", line 36, in get
    return self._index.forNodes(name)
java.lang.RuntimeExceptionPyRaisable: java.lang.IllegalArgumentException: No index provider 'lucene' found. Maybe the intended provider (or one more of its dependencies) aren't on the classpath or it failed to load.

谷歌搜索整个最后一行并没有去任何地方.只是搜索"java.lang.IllegalArgumentException:找不到索引提供者'lucene'." 在python的上下文中没有任何结果.

neo4j messages.log似乎显示数据库已打开3次(initDB(),testDB()和index()).每个实例的类路径相同:

Class Path: /ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-jmx-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-lucene-index-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-graph-matching-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-kernel-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/geronimo-jta_1.1_spec-1.1.1.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/lucene-core-3.1.0.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-graph-algo-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-udc-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/neo4j-cypher-1.5.M02.jar:/ht/dev/envFlask/local/lib/python2.7/site-packages/neo4j/javalib/scala-library-2.9.0-1.jar

我还直接将index()修改为connectDB和attachThreadToJVM,如initDB()和testDB(),而不使用'g'全局 - 这导致完全相同的错误.

我可能缺少什么/忽略让neo4j-embedded和jpype处理线程请求而不只是在'main'应用程序中？

注意:我知道使用py2neo或Rexster/Bulbs的RESTful Web服务解决方案,但我现在想要避免这种情况.

编辑:使用JPype-0.5.4.2,Neo4j-embedded-1.5.b2,Java-6-openjdk

此模式的一个问题是您冒着启动指向同一位置的多个数据库的风险,这将导致问题.您需要的是在应用程序的整个生命周期之后的数据库的单个实例.

为什么它没有找到lucene提供者是一个更难的问题..索引提供程序是使用java服务加载器加载的,这意味着JPype不应该影响它.只要JVM启动正常,并且lucene-index实现jar在类路径上,它应该可以工作.

它可能与某种程度上的线程有关,我正在编写一个修复程序来自动处理"attachThreadToJVM()"调用.我将添加一个测试用例,以确保从单独的线程读取索引也能按预期工作.

线程工作目前在此邮件列表线程中保持更新:

http://neo4j-community-discussions.438527.n3.nabble.com/Neo4j-Python-embedding-problems-with-shutdown-and-threads-td3476163.html