使用线程加速上下文管理器的缓慢初始化

Question

I am consuming from a python2.7 module which I cannot easily change. This module has a factory for a class that is a context manager. This works great for managing the lifetime of the object, but initializing this class involves waiting on creation of a cloud based resource and it can take many minutes to run. Within the scope of my program I need to create two of the objects such as the following:

import immutable_module

cloud_resource_name1 = "load_ai_model"
cloud_resource_name2 = "create_input_output_model"

with immutable_module.create_remote_cloud_resource(cloud_resource_name1) as a, \
     immutable_module.create_remote_cloud_resource(cloud_resource_name2) as b: 
    result = __do_imporant_thing(a, b)

print(result)

Is there a way call these two contextmanagers concurrently using threads to speed up the load time?

Answer 1

After doing more research I found a solution, but it may not be the best answer. The solution relies on calling __enter__ and __exit__ manually for the contextmanager.

import immutable_module

cloud_resource_name1 = "load_ai_model"
cloud_resource_name2 = "create_input_output_model"

a_context = immutable_module.create_remote_cloud_resource(cloud_resource_name1) 
b_context = immutable_module.create_remote_cloud_resource(cloud_resource_name2)

a = None
b = None

try:
    def __set_a():
      global a
      a = a_context.__enter__()

    def __set_b():
      global b
      b = b_context.__enter__()

    a_thread = Thread(target=__set_a)
    b_thread = Thread(target=__set_b)

    a_thread.start()
    b_thread.start()

    a_thread.join()
    b_thread.join()

    result = __do_imporant_thing(a, b)

finally:
    try:
        if a is not None:
            a_context.__exit__(*sys.exc_info())
    finally:
        if b is not None:
            b_context.__exit__(*sys.exc_info())

print(result)

This is really dirty, not generic at all, and there are potential issues with exception handling, but it works.