kotlin - 如何使用超时值同步调用异步请求？

Question

我必须同步调用异步 api 请求。由于此 api 请求需要很长时间才能回答，我还想设置一个超时以使 api 请求失败并继续 null。这是我调用此 api 的代码:

private suspend fun call(
    accessStage: AccessStage,
): Response? = withContext<Response?>(Dispatchers.IO) {

    return@withContext withTimeoutOrNull(1000) {

        suspendCoroutine<Response?> { continuation ->

            val request = External3rdPartyApi.newRequest(
                accessStage
            ) { response, throwable ->

                continuation.resume(response)
            }

            request.parameters = hashMapOf<String, String>().apply {
                put["token"] = External3rdPartyApi.TOKEN
                put["salt"] = External3rdPartyApi.calculateSalt(accessStage)
            }
            request.executeAsync()
        }
    }
}

我无法更改 External3rdPartyApi 的工作方式。

我认为上面的代码看起来很糟糕。另外，我读了 another answer :

withTimeout { ... } is designed to cancel the ongoing operation on timeout, which is only possible if the operation in question is cancellable.

那么，我应该使用 suspendCancellableCoroutine 而不是 suspendCoroutine 吗？

我怎样才能写得更好？

Answer 1

如果您不能(或不想)处理协程的取消，则使用 suspendCoroutine 没问题。但是因为你有超时，你应该考虑使用 suspendCancellableCoroutine并处理取消事件以停止工作(在第三方功能中 - 如果可以的话)。

suspendCancellableCoroutine<T> { continuation ->
  continuation.invokeOnCancellation { throwable ->
    // now you could stop your (third party) work  
  }        
}

当您的第三方函数抛出异常时，您可以 try catch 它并使用 exception 恢复或返回 null 值(取决于您的用例):

suspendCancellableCoroutine<T?> { continuation ->
  try {
    continuation.resume(thirdParty.call())
  } catch (e: Exception) {
    // resume with exception
    continuation.resumeWithException(e)
    // or just return null and swallow the exception
    continuation.resume(null)
  }   
}

让我们把所有的放在一起

suspend fun call(): Response? = withContext(Dispatchers.IO) {
  return@withContext withTimeoutOrNull(1000L) {
    return@withTimeoutOrNull suspendCancellableCoroutine { continuation ->
      try {
        continuation.resume(External3rdPartyApi.newRequest(accessStage))
      } catch (e: Exception) {
        // resume with exception
        continuation.resumeWithException(e)
        
        // or just return null and swallow the exception
        continuation.resume(null)
      }
         
      // in case the coroutine gets cancelled - because of timeout or something else
      continuation.invokeOnCancellation {
        // stop all the work
      }
    }
  }
}