如何解决InheritableThreadLocal和线程池搭配使用的问题

在使用线程池时，可能会遇到InheritableThreadLocal无法正确继承的问题。这是因为线程池在执行任务时会重用之前创建的线程，而这些线程可能已经绑定了旧的InheritableThreadLocal值，导致新任务继承错误的值。解决这个问题的办法是使用ThreadPoolExecutor而不是ThreadPool来创建线程池，并覆盖它的`ThreadFactory`方法，以创建一个新的线程并正确地继承InheritableThreadLocal值。具体来说，可以创建一个实现`ThreadFactory`接口的类，并覆盖`newThread`方法，如下所示: [^2]

import threading
from concurrent.futures import ThreadPoolExecutor, _base

class MyThreadLocal(_base.Executor):
    
    def __init__(self, thread_local):
        self.thread_local = thread_local
    
    def submit(self, fn, *args, **kwargs):
        return super().submit(self.wrapper(fn), *args, **kwargs)
    
    def wrapper(self, fn):
        local = self.thread_local.copy()
        def wrapped_fn(*args, **kwargs):
            with local:
                return fn(*args, **kwargs)
        return wrapped_fn
    
    def map(self, fn, *iterables, timeout=None, chunksize=1):
        return list(self._map_async(fn, *iterables).result(timeout=timeout))
    
    def shutdown(self, wait=True):
        pass
        
class MyThreadFactory(ThreadPoolExecutor):
    
    def __init__(self, thread_local, *args, **kwargs):
        self.thread_local = thread_local
        super().__init__(*args, **kwargs)
        
    def new_thread(self, executor, task):
        t = threading.Thread(target=executor._worker, args=(task,), daemon=True)
        t.daemon = False
        t.name = None
        t._Thread__ident = None
        t._target = None
        t._args = None
        t._kwargs = None
        t._state = threading.S
        t._thread_local = self.thread_local
        return t

# 使用示例：
import random
import time

def test_inheritable_thread_local(thread_local, pool):
    thread_local.value = random.randint(0, 100)
    pool.submit(worker, thread_local.copy())

def worker(thread_local_copy):
    print(thread_local_copy.value)
    time.sleep(1)
    print(thread_local_copy.value)

if __name__ == '__main__':
    thread_local = threading.local()
    pool = MyThreadLocal(thread_local)
    factory = MyThreadFactory(thread_local, 5)
    pool._threads = set()
    pool._max_workers = 5
    pool._thread_name_prefix = 'ThreadPoolExecutor-'
    pool._initializer = None
    pool._initargs = ()
    pool._queue = queue.Queue()
    pool._task_counter = itertools.count()
    pool._shutdown = False
    pool._results = {}
    pool._work_ids = set()
    pool._threads_lock = threading.Lock()
    pool._threads_recreate_lock = threading.Lock()
    pool._pending_work_items_lock = threading.Lock()
    pool._wake_up_mutex = threading.Lock()
    pool._not_responsive_workers = set()
    pool._shutdown_thread = None
    pool._shutdown_lock = threading.Lock()
    pool._shutdown_cond = threading.Condition(pool._shutdown_lock)
    pool._workers = {}
    pool._done_with_recreate = threading.Condition()
    pool._threads_recreate_override = False
    pool._threads_recreate_count = 0
    pool._threads_recreate_next_id = 0
    pool._threads_recreate_idle_time = 0.0
    pool._threads_recreate_rate = 0.5
    pool._threads_recreate_max = 5
    pool._threads_recreate_last = 0.0
    pool._threads_recreate_reset = False
    pool._kill_workers = False
    pool._force_workers = set()
    pool._shutdown_lock = threading.Lock()
    pool._shutdown_cond = threading.Condition(pool._shutdown_lock)
    pool._stop_f = None
    pool._threads_recreate_condition = threading.Condition(pool._threads_recreate_lock)
    pool._thread_factory = factory
    test_inheritable_thread_local(thread_local, pool)
    pool.shutdown()