分享一個異步任務在遇到IO異常時支持遞歸回調的輔助方法

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}",                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;        }        if (t.IsCanceled)        {            _logger.ErrorFormat("Async task '{0}' was cancelled, contextInfo:{1}, current retryTimes:{2}",                asyncActionName, getContextInfoFunc(), retryTimes);            retryAction(retryTimes);            return;        }        var result = t.Result;        if (result.Status == AsyncOperationResultStatus.IOException)        {            _logger.ErrorFormat("Async task '{0}' has io exception, contextInfo:{1}, current retryTimes:{2}, errorMsg:{3}",                asyncActionName, getContextInfoFunc(), retryTimes, result.ErrorMessage);            retryAction(retryTimes);            return;        }        if (successAction != null)        {            successAction(result);        }    });    try    {        asyncAction().ContinueWith(completeAction);    }    catch (IOException ex)    {        _logger.Error(string.Format("Execute async action '{0}' failed, contextInfo:{1}, current retryTimes:{2}",            asyncActionName, getContextInfoFunc(), retryTimes), ex);        retryAction(retryTimes);    }    catch (Exception ex)    {        _logger.Error(string.Format("Execute async action '{0}' failed, contextInfo:{1}, current retryTimes:{2}",            asyncActionName, getContextInfoFunc(), retryTimes), ex);        executeFailedAction(ex);    }}

該函數的功能是：執行一個異步任務（返回Task的方法），如果執行出現IO異常，則重試當前主函數（mainAction）；用戶的mainAction中會再次調用TryAsyncActionRecursively方法。從而實現當遇到IO異常時，能做到不斷重試。另外，重試只立即重試指定的次數，超過指定次數，則不立即重試，而是暫停一定間隔后再次執行。該函數還提供當acyncAction執行成功或失敗后的回調函數，以及允許傳入當前上下文的一些說明信息，以便記錄有意義的錯誤日志信息。

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));    },    () => string.Format("[eventStream:{0}]", eventStream),    ex => processingCommand.Complete(new CommandResult(CommandStatus.Failed, processingCommand.Command.Id)),    retryTimes);}

PublishEventAsync(processingCommand, eventStream, 0);