tl; dr

Question

tl; dr

如何序列化Flask应用程序或请求上下文，或该上下文的子集（即可以成功序列化的任何），以便可以从以下位置访问该上下文另一个进程，而不是线程？

长版

我有一些功能需要访问要在后台运行的Flask请求上下文或App上下文。

Flask具有内置的@copy_current_request_context装饰器，用于将函数包装在请求上下文的副本中，因此您可以在其他线程中运行它：

from threading import Thread
from flask import Flask, request, copy_current_request_context

app = Flask(__name__)

@app.route('/')
def index():
    request.foo = 'bar'
    @copy_current_request_context
    def baz():
        print(request.foo)
    thr = Thread(target=baz)
    thr.start()
    return 'ok'

虽然Flask没有提供内置的装饰器来复制应用上下文，但它提供了执行此操作的机制-Access flask.g inside greenlet

中描述了一种解决方案

我尝试过的

首先，我希望和Pickle一起解决。 concurrent.futures.ProcessPoolExecutor使用的就是这个。不幸的是，由于在应用程序上下文中存在线程锁定对象，因此Pickle失败：

>>> with app.test_request_context('/'):
...     pickle.dumps(appctx)
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
TypeError: can't pickle _thread.lock objects

它也不能复制修饰/包装的函数：

>>> with app.test_request_context('/'):
...     bar = copy_current_request_context(pow)
...     pickle.dumps(bar)
...
Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
_pickle.PicklingError: Can't pickle <function pow at 0x110bee8c8>: it's not the same object as builtins.pow

接下来，我尝试了dill。它通过了以上两个测试，但是无法序列化可能在上下文中出现的许多其他事情。应用程序上下文尤其容易在扩展中链接自身：SQLAlchemy是一个很好的例子。当您使用SQLAlchemy并尝试序列化您的应用上下文时，会发生以下情况：

>>> from flask_sqlalchemy import SQLAlchemy
>>> db = SQLAlchemy(app)
>>> with app.test_request_context('/'):
...     from flask.globals import _app_ctx_stack
...     appctx = _app_ctx_stack.top
...     dill.dumps(appctx)
...
Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
  File "/Users/dchevell/Development/python3/sandbox/env/lib/python3.7/site-packages/dill/_dill.py", line 294, in dumps
    dump(obj, file, protocol, byref, fmode, recurse)#, strictio)
  File "/Users/dchevell/Development/python3/sandbox/env/lib/python3.7/site-packages/dill/_dill.py", line 287, in dump
    pik.dump(obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 437, in dump
    self.save(obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 549, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 662, in save_reduce
    save(state)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/dchevell/Development/python3/sandbox/env/lib/python3.7/site-packages/dill/_dill.py", line 902, in save_module_dict
    StockPickler.save_dict(pickler, obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 856, in save_dict
    self._batch_setitems(obj.items())
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 882, in _batch_setitems
    save(v)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 549, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 662, in save_reduce
    save(state)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/dchevell/Development/python3/sandbox/env/lib/python3.7/site-packages/dill/_dill.py", line 902, in save_module_dict
    StockPickler.save_dict(pickler, obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 856, in save_dict
    self._batch_setitems(obj.items())
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 882, in _batch_setitems
    save(v)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 816, in save_list
    self._batch_appends(obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 843, in _batch_appends
    save(tmp[0])
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/dchevell/Development/python3/sandbox/env/lib/python3.7/site-packages/dill/_dill.py", line 1386, in save_function
    obj.__dict__), obj=obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 638, in save_reduce
    save(args)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 786, in save_tuple
    save(element)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 771, in save_tuple
    save(element)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/dchevell/Development/python3/sandbox/env/lib/python3.7/site-packages/dill/_dill.py", line 1129, in save_cell
    pickler.save_reduce(_create_cell, (f,), obj=obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 638, in save_reduce
    save(args)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 771, in save_tuple
    save(element)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 549, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 662, in save_reduce
    save(state)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/dchevell/Development/python3/sandbox/env/lib/python3.7/site-packages/dill/_dill.py", line 902, in save_module_dict
    StockPickler.save_dict(pickler, obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 856, in save_dict
    self._batch_setitems(obj.items())
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 882, in _batch_setitems
    save(v)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 549, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 662, in save_reduce
    save(state)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/dchevell/Development/python3/sandbox/env/lib/python3.7/site-packages/dill/_dill.py", line 902, in save_module_dict
    StockPickler.save_dict(pickler, obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 856, in save_dict
    self._batch_setitems(obj.items())
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 882, in _batch_setitems
    save(v)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 549, in save
    self.save_reduce(obj=obj, *rv)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 662, in save_reduce
    save(state)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/dchevell/Development/python3/sandbox/env/lib/python3.7/site-packages/dill/_dill.py", line 902, in save_module_dict
    StockPickler.save_dict(pickler, obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 856, in save_dict
    self._batch_setitems(obj.items())
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 882, in _batch_setitems
    save(v)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/dchevell/Development/python3/sandbox/env/lib/python3.7/site-packages/dill/_dill.py", line 1330, in save_type
    StockPickler.save_global(pickler, obj)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 957, in save_global
    (obj, module_name, name)) from None
_pickle.PicklingError: Can't pickle <class 'sqlalchemy.orm.session.SignallingSession'>: it's not found as sqlalchemy.orm.session.SignallingSession

所以：有什么办法解决这个问题？我曾经以为是“及时”分叉一个新流程（即，在我要运行后台任务之前）可能意味着我什至根本不需要复制上下文，只要它已经存在就可以分支在设置上下文后发生。我不知道如何使用ProcessPoolExecutor来完成这项工作，因为流程是一个长期存在的池。我唯一想做的就是以某种方式强制工作者进程在每个任务结束时关闭，但是我很确定这只会导致池中断。

Answer 1

不确定这是否适合您，但有可能使用来自其他进程的 Flask 应用程序上下文。它要求您使用 application factory 模式。

# your_project/app.py

def create_app(config_file):
    # Load the config file somehow
    # Create your app instance
    app = Flask(__name__)
    # Initialize your extensions
    db.init_app(app)
    # Mount routes, etc
    app.register_blueprint(...)
    # Return your app
    return app

# your_project/wsgi.py
from .app import create_app

app = create_app("./config/local.cfg")

您定义一个应用程序工厂并使用它来创建您的应用程序作为 wsgi.py 或其他方便位置的入口点，您稍后可以从将在另一个进程中运行的后台脚本访问此应用程序实例。< /p>


# your_project/background_script.py
from .wsgi import app

with app.app_context():
    # Do some stuff

顺便说一句，这也是将 Flask 与 Celery 一起使用的一种方式，例如，如in this question 所述。希望这对您有所帮助。

将Flask请求/应用上下文复制到另一个进程

tl; dr

长版

我尝试过的

1 个答案: