Python相當於TaskCompletionSource的情況 <T> （。凈）？

Question

我正在嘗試實現以下偽代碼（部分受.NET中TaskCompletionSource<T>啟發），其目的是等待接收到特定事件以繼續執行（或引發TimeoutError ）：

from axel import Event

def _wait_for_provider_up(self, data_provider: Provider, ms_timeout: int) -> bool:
    if provider.State == ProviderState.Connected: return True
    if provider.State == ProviderState.Faulted: return False
    taskCompletion = TaskCompletionSource<bool>()

    def onStateChanged(sender, e: ProviderStateChangedEventArgs):
        if e.State == ProviderState.Connected:
            taskCompletion.TrySetResult(True)
        elif e.State == ProviderState.Faulted:
            taskCompletion.TrySetResult(False)

    provider.StateChanged += onStateChanged
    try:
        if provider.State == ProviderState.Connected: return True
        elif provider.State == ProviderState.Faulted: return False
        if not taskCompletion.Task.Wait(ms_timeout) or not taskCompletion.Task.Result or provider.State != ProviderState.Connected:
            return False
    finally:
        provider.StateChanged -= onStateChanged
    return True

什么是推薦的pythonic（或.NET風格但與python兼容）的方法來實現這一目標？

Answer 1

我試圖以asyncio方式重寫您的代碼，但請注意： _wait_for_provider_up函數已更改為coroutine ：

from axel import Event

async def _wait_for_provider_up(self, data_provider: Provider, ms_timeout: int) -> bool:
    if provider.State == ProviderState.Connected: 
        return True
    if provider.State == ProviderState.Faulted: 
        return False
    taskCompletion = asyncio.Future()

    def onStateChanged(sender, e: ProviderStateChangedEventArgs):
        if e.State == ProviderState.Connected:
            taskCompletion.set_result(True)
        elif e.State == ProviderState.Faulted:
            taskCompletion.set_result(False)

    provider.StateChanged += onStateChanged
    try:
        if provider.State == ProviderState.Connected: 
            return True
        elif provider.State == ProviderState.Faulted: 
            return False
        try:
            result = await asyncio.wait_for(taskCompletion, timeout=ms_timeout/1000)
            if not result or provider.State != ProviderState.Connected:
                return False
        except asyncio.TimeoutError:
            return False  
    finally:
        provider.StateChanged -= onStateChanged
    return True

該代碼仍然不是很Python，但是希望您能理解我的意思。

Answer 2

python等效項是asyncio.Future 。

import asyncio
source = asyncio.Future()

async def await_concat(x):
    return x + await source


async def set_after_two_seconds():
    print("READY")
    await asyncio.sleep(2)
    print("SET")
    source.set_result("GO")

print(asyncio.get_event_loop().run_until_complete(asyncio.gather(
    await_concat("PASS "),
    set_after_two_seconds(),
)))

## prints
# READY
## (note: two second pause here)
# SET
# ['PASS GO', None]

Answer 3

假設提供者是python線程。 您可以使用join（timeout）方法，該方法等待線程競爭或超時。 join（）始終返回None，因此要檢查線程是否仍在運行，您需要使用isAlive（）。 這是實現taskCompletion的一種選擇

def taskCompletion(thread,timeout): 
   thread.join(timeout) 
   return isAlive()