分享一个异步任务在遇到IO异常时支持递归回调的辅助方法

public void TryAsyncActionRecursively<TAsyncResult>(
    string asyncActionName,
    Func<Task<TAsyncResult>> asyncAction,
    Action<int> mainAction,
    Action<TAsyncResult> successAction,
    Func<string> getContextInfoFunc,
    Action<Exception> failedAction,
    int retryTimes) where TAsyncResult : AsyncOperationResult
{
    var retryAction = new Action<int>(currentRetryTimes =>
    {
        if (currentRetryTimes > _immediatelyRetryTimes)
        {
            Task.Factory.StartDelayedTask(_retryIntervalForIOException, () => mainAction(currentRetryTimes + 1));
        }
        else
        {
            mainAction(currentRetryTimes + 1);
        }
    });
    var executeFailedAction = new Action<Exception>(ex =>
    {
        try
        {
            if (failedAction != null)
            {
                failedAction(ex);
            }
        }
        catch (Exception unknownEx)
        {
            _logger.Error(string.Format("Failed to execute the failedCallbackAction of asyncAction:{0}, contextInfo:{1}",
                asyncActionName, getContextInfoFunc()), unknownEx);
        }
    });
    var processTaskException = new Action<Exception, int>((ex, currentRetryTimes) =>
    {
        if (ex is IOException)
        {
            _logger.Error(string.Format("Async task ‘{0}‘ has io exception, contextInfo:{1}, current retryTimes:{2}, try to run the async task again.",
                asyncActionName, getContextInfoFunc(), currentRetryTimes), ex);
            retryAction(retryTimes);
        }
        else
        {
            _logger.Error(string.Format("Async task ‘{0}‘ has unknown exception, contextInfo:{1}, current retryTimes:{2}",
                asyncActionName, getContextInfoFunc(), currentRetryTimes), ex);            executeFailedAction(ex);
        }
    });
    var completeAction = new Action<Task<TAsyncResult>>(t =>
    {
        if (t.Exception != null)
        {
            processTaskException(t.Exception.InnerException, retryTimes);
            return;
        }
        var result = t.Result;
        if (result.Status == AsyncOperationResultStatus.IOException)
        {
            _logger.ErrorFormat("Async task ‘{0}‘ result status is io exception, contextInfo:{1}, current retryTimes:{2}, errorMsg:{3}, try to run the async task again.",
                asyncActionName, getContextInfoFunc(), retryTimes, result.ErrorMessage);
            retryAction(retryTimes);
            return;
        }
        if (successAction != null)
        {
            successAction(result);
        }
    });

    try
    {
        asyncAction().ContinueWith(completeAction);
    }
    catch (IOException ex)
    {
        _logger.Error(string.Format("IOException raised when executing async action ‘{0}‘, contextInfo:{1}, current retryTimes:{2}, try to run the async task again.",
            asyncActionName, getContextInfoFunc(), retryTimes), ex);
        retryAction(retryTimes);
    }
    catch (Exception ex)
    {
        _logger.Error(string.Format("Unknown exception raised when executing async action ‘{0}‘, contextInfo:{1}, current retryTimes:{2}",
            asyncActionName, getContextInfoFunc(), retryTimes), ex);
        executeFailedAction(ex);
    }
}

该函数的功能是：执行一个异步任务（返回Task的方法），如果执行出现IO异常，则重试当前主函数（mainAction）；用户的mainAction中会再次调用TryAsyncActionRecursively方法。

从而实现当遇到IO异常时，能做到不断重试。另外，重试只立即重试指定的次数，超过指定次数，则不立即重试，而是暂停一定间隔后再次执行。

该函数还提供当acyncAction执行成功或失败后的回调函数，以及允许传入当前上下文的一些说明信息，以便记录有意义的错误日志信息。

下面是使用示例：

private void PublishEventAsync(ProcessingCommand processingCommand, EventStream eventStream, int retryTimes)
{
    TryAsyncActionRecursively<AsyncOperationResult>("PublishEventAsync",
    () => _eventPublisher.PublishAsync(eventStream),
    currentRetryTimes => PublishEventAsync(processingCommand, eventStream, currentRetryTimes),
    result =>
    {
        _logger.DebugFormat("Publish events success, {0}", eventStream);
        processingCommand.Complete(new CommandResult(CommandStatus.Success, processingCommand.Command.Id, null, null, null));
    },
    () => string.Format("[eventStream:{0}]", eventStream),
    ex => processingCommand.Complete(new CommandResult(CommandStatus.Failed, processingCommand.Command.Id, null, null, "Publish events failed.")),
    retryTimes);
}

PublishEventAsync(processingCommand, eventStream, 0);