python - python字典异步安全吗？

Question

我在我的 Python 应用程序中创建了一个字典，用于保存数据，并且我有两个任务同时运行并从外部 API 获取数据。一旦他们获得数据，他们就会更新字典——每个字典都有一个不同的键。
我想了解字典是否是异步安全的，还是在读取/更新字典时需要加锁？
任务还每次读取最后保存的值。

my_data = {}
asyncio.create_task(call_func_one_coroutine)
asyncio.create_task(call_func_two_coroutine)

async def call_func_one_coroutine():
  data =  await goto_api_get_data()
  my_data['one'] = data + my_data['one']


async def call_func_two_coroutine():
  data =  await goto_api_another_get_data()
  my_data['two'] = data + my_data['two']

Answer 1

I want to understand if the dictionary is async safe or do I need to put a lock when the dictionary is read/updated?

Asyncio 基于协作式多任务处理，只能在显式 await 处切换任务表达式或在 async with和 async for声明。由于单个字典的更新永远不会涉及等待(等待必须在更新开始之前完成)，因此就异步多任务而言，它实际上是原子的，您不需要锁定它。这适用于从异步代码访问的所有数据结构。
再举一个没有问题的例子:

# correct - there are no awaits between two accesses to the dict d
key = await key_queue.get()
if key in d:
    d[key] = calc_value(key)

一个 dict 修改不是异步安全的示例将涉及对由 await 分隔的 dict 的多次访问。 s。例如:

# incorrect, d[key] could appear while we're reading the value,
# in which case we'd clobber the existing key
if key not in d:
    d[key] = await read_value()

要更正它，您可以在 await 之后添加另一个检查，或使用显式锁:

# correct (1), using double check
if key not in d:
    value = await read_value()
    # Check again whether the key is vacant. Since there are no awaits
    # between this check and the update, the operation is atomic.
    if key not in d:
        d[key] = value

# correct (2), using a shared asyncio.Lock:
async with d_lock:
    # Single check is sufficient because the lock ensures that
    # no one can modify the dict while we're reading the value.
    if key not in d:
        d[key] = await read_value()