Polly：如何结合TimeoutPolicy和RetryPolicy请求功能

分类：编程问答

如何解决Polly：如何结合TimeoutPolicy和RetryPolicy请求功能

我正在尝试将TimeoutPolicy和RetryPolicy结合在一起以进行Func中的API调用，但是我没有找到一种方法来实现这一目标。

如果我仅使用RetryPolicy，就可以正常工作。

我有一个GetRequest方法，该方法调用HttpClient并返回数据：

async Task<Data> GetRequest(string api,int id)
{
    var httpClient = new HttpClient();
    var response = await httpClient.GetAsync($"{api}{id}");

    var rawResponse = await response.Content.ReadAsStringAsync();
    return JsonConvert.DeserializeObject<Data>(rawResponse);
}

我也有Func可以将调用嵌入到此方法中： var func = new Func<Task<Data>>(() => GetRequest(api,i));

我这样称呼服务： Results.Add(await _networkService.RetryWithoutTimeout<Data>(func,3,OnRetry));

此RetryWithoutTimeout方法如下：

async Task<T> RetryWithoutTimeout<T>(Func<Task<T>> func,int retryCount = 1,Func<Exception,int,Task> onRetry = null)
{
    var onRetryInner = new Func<Exception,Task>((e,i) =>
    {
        return Task.Factory.StartNew(() => {
#if DEBUG
            System.Diagnostics.Debug.WriteLine($"Retry #{i} due to exception '{(e.InnerException ?? e).Message}'");
#endif
        });
    });

    return await Policy.Handle<Exception>()
                        .RetryAsync(retryCount,onRetry ?? onRetryInner)
                        .ExecuteAsync<T>(func);
}

我已使用新的TimeoutPolicy方法将此代码更新为使用RetryWithTimeout：

async Task<T> RetryWithTimeout<T>(Func<Task<T>> func,Task> onRetry = null,int timeoutDelay = 30)
{
    var onRetryInner = new Func<Exception,i) =>
    {
        return Task.Factory.StartNew(() => {
#if DEBUG
            System.Diagnostics.Debug.WriteLine($"Retry #{i} due to exception '{(e.InnerException ?? e).Message}'");
#endif
        });
    });

    var retryPolicy = Policy
        .Handle<Exception>()
        .RetryAsync(retryCount,onRetry ?? onRetryInner);

    var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromSeconds(timeoutDelay));

    var policyWrap = timeoutPolicy.WrapAsync((IAsyncPolicy)retryPolicy);

    return await policyWrap.ExecuteAsync(
                    async ct => await Task.Run(func),CancellationToken.None
                    );
}

但是我看不到如何管理GetRequest()方法：我所有的测试都失败了...

编辑： 我已经基于@Peter Csala评论创建了一个示例。

因此，第一，我刚刚更新了重试次数，以检查retryPolicy是否正确应用：

private const int TimeoutInMilliseconds = 2500;
private const int MaxRetries = 3;
private static int _times;

static async Task Main(string[] args)
{
    try
    {
        await RetryWithTimeout(TestStrategy,MaxRetries);
    }
    catch (Exception ex)
    {
        WriteLine($"{nameof(Main)} - Exception - Failed due to: {ex.Message}");
    }
    Console.ReadKey();
}

private static async Task<string> TestStrategy(CancellationToken ct)
{
    WriteLine($"{nameof(TestStrategy)} has been called for the {_times++}th times.");
    await Task.Delay(TimeoutInMilliseconds * 2,ct);
    return "Finished";
}

internal static async Task<T> RetryWithTimeout<T>(Func<CancellationToken,Task<T>> func,int timeoutDelay = TimeoutInMilliseconds)
{
    WriteLine($"NetworkService - {nameof(RetryWithTimeout)}");
    var onRetryInner = new Func<Exception,i) =>
    {
        WriteLine($"NetworkService - {nameof(RetryWithTimeout)} #{i} due to exception '{(e.InnerException ?? e).Message}'");
        return Task.CompletedTask;
    });

    var retryPolicy = Policy
        .Handle<Exception>()
        .RetryAsync(retryCount,onRetry ?? onRetryInner);

    var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromMilliseconds(timeoutDelay));

    var policyWrap = Policy.WrapAsync(retryPolicy,timeoutPolicy); //Important part #1

    return await policyWrap.ExecuteAsync(
                    async ct => await func(ct),//Important part #2
                    CancellationToken.None);
}

关于日志，情况很好：

NetworkService - RetryWithTimeout
TestStrategy has been called for the 0th times.
NetworkService - RetryWithTimeout - Retry #1 due to exception 'A task was canceled.'
TestStrategy has been called for the 1th times.
NetworkService - RetryWithTimeout - Retry #2 due to exception 'A task was canceled.'
TestStrategy has been called for the 2th times.
NetworkService - RetryWithTimeout - Retry #3 due to exception 'A task was canceled.'
TestStrategy has been called for the 3th times.
Main - TimeoutRejectedException - Failed due to: The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.

然后，由于我需要全局超时，因此我更改了policyWrap：

private static async Task<string> TestStrategy(CancellationToken ct)
{
    WriteLine($"{nameof(TestStrategy)} has been called for the {_times++}th times.");
    await Task.Delay(1500,ct);
    throw new Exception("simulate Exception");
}

var policyWrap = timeoutPolicy.WrapAsync(retryPolicy);

关于日志，这也是正确的：

TestStrategy has been called for the 0th times.
NetworkService - RetryWithTimeout #1 due to exception 'simulate Exception'
TestStrategy has been called for the 1th times.
NetworkService - RetryWithTimeout #2 due to exception 'A task was canceled.'
Main - TimeoutRejectedException - Failed due to: The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.

之后，我实现了一种调用API的方法，该方法带有一些Exceptions，以更贴近我的需求：

static async Task Main(string[] args)
{
    try
    {
        await RetryWithTimeout(GetClientAsync,MaxRetries);
    }
    catch (TimeoutRejectedException trEx)
    {
        WriteLine($"{nameof(Main)} - TimeoutRejectedException - Failed due to: {trEx.Message}");
    }
    catch (WebException wEx)
    {
        WriteLine($"{nameof(Main)} - WebException - Failed due to: {wEx.Message}");
    }
    catch (Exception ex)
    {
        WriteLine($"{nameof(Main)} - Exception - Failed due to: {ex.Message}");
    }
    Console.ReadKey();
}

private static async Task<CountriesResponse> GetClientAsync(CancellationToken ct)
{
    WriteLine($"{nameof(GetClientAsync)} has been called for the {_times++}th times.");
    HttpClient _client = new HttpClient();
    try
    {
        var response = await _client.GetAsync(apiUri,ct);
        // ! The server response is faked through a Proxy and returns 500 answer !
        if (!response.IsSuccessStatusCode)
        {
            WriteLine($"{nameof(GetClientAsync)} - !response.IsSuccessStatusCode");
            throw new WebException($"No success status code {response.StatusCode}");
        }
        var rawResponse = await response.Content.ReadAsStringAsync();
        WriteLine($"{nameof(GetClientAsync)} - Finished");
        return JsonConvert.DeserializeObject<CountriesResponse>(rawResponse);
    }
    catch (TimeoutRejectedException trEx)
    {
        WriteLine($"{nameof(GetClientAsync)} - TimeoutRejectedException : {trEx.Message}");
        throw trEx;
    }
    catch (WebException wEx)
    {
        WriteLine($"{nameof(GetClientAsync)} - WebException: {wEx.Message}");
        throw wEx;
    }
    catch (Exception ex)
    {
        WriteLine($"{nameof(GetClientAsync)} - other exception: {ex.Message}");
        throw ex;
    }
}

日志仍然正确：

NetworkService - RetryWithTimeout
GetClientAsync has been called for the 0th times.
GetClientAsync - !response.IsSuccessStatusCode
GetClientAsync - WebException: No success status code InternalServerError
NetworkService - RetryWithTimeout #1 due to exception 'No success status code InternalServerError'
GetClientAsync has been called for the 1th times.
GetClientAsync - !response.IsSuccessStatusCode
GetClientAsync - WebException: No success status code InternalServerError
NetworkService - RetryWithTimeout #2 due to exception 'No success status code InternalServerError'
GetClientAsync has been called for the 2th times.
GetClientAsync - !response.IsSuccessStatusCode
GetClientAsync - WebException: No success status code InternalServerError
NetworkService - RetryWithTimeout #3 due to exception 'No success status code InternalServerError'
GetClientAsync has been called for the 3th times.
GetClientAsync - other exception: The operation was canceled.
Main - TimeoutRejectedException - Failed due to: The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.

最后，我希望能够调用一个“通用”方法，该方法可以在每个API调用中重复使用。此方法将如下所示：

static async Task<T> ProcessGetRequest<T>(Uri uri,CancellationToken ct)
{
    WriteLine("ApiService - ProcessGetRequest()");

    HttpClient _client = new HttpClient();

    var response = await _client.GetAsync(uri);
    if (!response.IsSuccessStatusCode)
    {
        WriteLine("ApiService - ProcessGetRequest() - !response.IsSuccessStatusCode");
        throw new WebException($"No success status code {response.StatusCode}");
    }
    var rawResponse = await response.Content.ReadAsStringAsync();

    return JsonConvert.DeserializeObject<T>(rawResponse);
}

但是，为此，我必须同时通过CancellationToken传递Uri和Api RetryWithTimeout，但我不知道如何管理它。

我试图通过以下方式更改RetryWithTimeout的签名：

internal static async Task<T> RetryWithTimeout<T>(Func<Uri,CancellationToken,int timeoutDelay = TimeoutInMilliseconds)

但是我找不到如何管理Func ...

您有想法或解释吗？

解决方法

您需要将CancellationToken传递到要取消的（由于超时）功能。

因此，假设您具有以下简化方法：

private const int TimeoutInMilliseconds = 1000;
private static int _times;
private static async Task<string> TestStrategy(CancellationToken ct)
{
    Console.WriteLine($"{nameof(TestStrategy)} has been called for the {_times++}th times.");
    await Task.Delay(TimeoutInMilliseconds * 2,ct);
    return "Finished";
}

因此，您的RetryWithTimeout可以像这样调整/修改：

static async Task<T> RetryWithTimeout<T>(Func<CancellationToken,Task<T>> func,int retryCount = 1,Func<Exception,int,Task> onRetry = null,int timeoutDelay = TimeoutInMilliseconds)
{
    var onRetryInner = new Func<Exception,Task>((e,i) =>
    {
        Console.WriteLine($"Retry #{i} due to exception '{(e.InnerException ?? e).Message}'");
        return Task.CompletedTask;
    });

    var retryPolicy = Policy
        .Handle<Exception>()
        .RetryAsync(retryCount,onRetry ?? onRetryInner);

    var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromMilliseconds(timeoutDelay));

    var policyWrap = Policy.WrapAsync(retryPolicy,timeoutPolicy); //Important part #1

    return await policyWrap.ExecuteAsync(
                    async ct => await func(ct),//Important part #2
                    CancellationToken.None);
}

重要的部分＃1-重试是外部的，超时是内部的策略
重要部分＃2-由于超时，CancellationToken传递给了要取消的功能

以下用法

static async Task Main(string[] args)
{
    try
    {
        await RetryWithTimeout(TestStrategy);
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Failed due to: {ex.Message}");
    }

    Console.ReadKey();
}

将产生以下输出：

TestStrategy has been called for the 0th times.
Retry #1 due to exception 'A task was canceled.'
TestStrategy has been called for the 1th times.
Failed due to: The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.

请记住，重试开始之前有0次尝试。

,

我终于找到了一个可行的解决方案，该解决方案已由@Peter Csala完成。

[
    {
        "NODE": "rabbit@server567","EXCLUSIVE": false,"NAME": "test-01","SYNCHRONISED_SLAVE_NODES": [],"SLAVE_NODES": [],"AUTO_DELETE": false,"VHOST": "/","ARGUMENTS": {},"TYPE": "classic","DURABLE": false
    },{
        "NODE": "rabbit@server567","NAME": "test-02","NAME": "test-03",{
        "MESSAGES_UNACKNOWLEDGED_RAM": 0,"RECOVERABLE_SLAVES": null,"CONSUMERS": 0,"REDUCTIONS": 9700519,"MESSAGE_BYTES_PAGED_OUT": 0,"MESSAGE_BYTES_UNACKNOWLEDGED": 0,"REDUCTIONS_DETAILS": {
            "RATE": 0.0
        },"MESSAGE_BYTES": 0,"MESSAGES_UNACKNOWLEDGED": 0,"CONSUMER_UTILISATION": null,"GARBAGE_COLLECTION": {
            "MAX_HEAP_SIZE": 0,"MIN_HEAP_SIZE": 233,"FULLSWEEP_AFTER": 65535,"MINOR_GCS": 15635,"MIN_BIN_VHEAP_SIZE": 46422
        },"MESSAGES_DETAILS": {
            "RATE": 0.0
        },"SLAVE_NODES": [
            "rabbit@server567"
        ],"MESSAGE_BYTES_PERSISTENT": 0,"POLICY": "ha-all","MESSAGES_PAGED_OUT": 0,"NODE": "rabbit@server566","HEAD_MESSAGE_TIMESTAMP": null,"DURABLE": false,"MESSAGES_READY_RAM": 0,"STATE": "running","EFFECTIVE_POLICY_DEFINITION": {
            "HA-MODE": "all"
        },"MESSAGES_READY": 0,"MESSAGES_RAM": 0,"MESSAGE_BYTES_READY": 0,"SINGLE_ACTIVE_CONSUMER_TAG": null,"NAME": "test-04","MESSAGES_PERSISTENT": 0,"BACKING_QUEUE_STATUS": {
            "MIRROR_SENDERS": 0,"Q1": 0,"Q3": 0,"Q2": 0,"Q4": 0,"AVG_ACK_EGRESS_RATE": 0.0,"MIRROR_SEEN": 0,"LEN": 0,"TARGET_RAM_COUNT": "infinity","MODE": "default","NEXT_SEQ_ID": 0,"DELTA": [
                "delta","undefined","undefined"
            ],"AVG_ACK_INGRESS_RATE": 0.0,"AVG_EGRESS_RATE": 0.0,"AVG_INGRESS_RATE": 0.0
        },"MESSAGES": 0,"IDLE_SINCE": "2020-10-16 13:50:50","OPERATOR_POLICY": null,"SYNCHRONISED_SLAVE_NODES": [
            "rabbit@server567"
        ],"MEMORY": 10556,"EXCLUSIVE_CONSUMER_TAG": null,"MESSAGES_READY_DETAILS": {
            "RATE": 0.0
        },"MESSAGES_UNACKNOWLEDGED_DETAILS": {
            "RATE": 0.0
        },"MESSAGE_BYTES_RAM": 0
    }
]

我得到这些结果：

private const int TimeoutInMilliseconds = 2500;
private const int MaxRetries = 3;

private static Uri apiUri = new Uri("https://api/param");
private static int _times;

public static Country[] Countries
{
    get;
    set;
}

static async Task Main(string[] args)
{
    try
    {
        await LoadCountriesWithRetry(false);
    }
    catch (Exception ex)
    {
        WriteLine($"{nameof(Main)} - Exception - Failed due to: {ex.Message}");
    }
    Console.ReadKey();
}

static async Task LoadCountriesWithRetry(bool shouldWaitAndRetry)
{
    WriteLine($"{nameof(LoadCountriesWithRetry)}");
    try
    {
        Countries = await GetCountriesWithRetry();
    }
    catch (TimeoutRejectedException trE)
    {
        WriteLine($"{nameof(LoadCountriesWithRetry)} - TimeoutRejectedException : {trE.Message}");
    }   
    catch (WebException wE)
    {
        WriteLine($"{nameof(LoadCountriesWithRetry)} - WebException : {wE.Message}");
    }
    catch (Exception e)
    {
        WriteLine($"{nameof(LoadCountriesWithRetry)} - Exception : {e.Message}");
    }
}

public static async Task<Country[]> GetCountriesWithRetry()
{
    WriteLine($"{nameof(GetCountriesWithRetry)}");
    var response = await GetAndRetry<CountriesResponse>(uri,MaxRetries);
    return response?.Countries;
}

static Func<CancellationToken,Task<T>> IssueRequest<T>(Uri uri) => ct => ProcessGetRequest<T>(ct,uri);

public static async Task<T> GetAndRetry<T>(Uri uri,int retryCount,Task> onRetry = null)
    where T : class
{
    WriteLine($"{nameof(GetAndRetry)}");
    return await RetryWithTimeout<T>(IssueRequest<T>(uri),retryCount);
}

static async Task<T> ProcessGetRequest<T>(CancellationToken ct,Uri uri)
{
    WriteLine($"{nameof(ProcessGetRequest)}");
    HttpClient _client = new HttpClient();
    var response = await _client.GetAsync(uri,ct);
    if (!response.IsSuccessStatusCode)
    {
        WriteLine($"{nameof(ProcessGetRequest)} - !response.IsSuccessStatusCode");
        throw new WebException($"No success status code {response.StatusCode}");
    }
    var rawResponse = await response.Content.ReadAsStringAsync();
    WriteLine($"{nameof(ProcessGetRequest)} - Success");
    return JsonConvert.DeserializeObject<T>(rawResponse);
}

internal static async Task<T> RetryWithTimeout<T>(Func<CancellationToken,Uri uri,int timeoutDelay = TimeoutInMilliseconds)
{
    WriteLine($"{nameof(RetryWithTimeout)}");
    var onRetryInner = new Func<Exception,i) =>
    {
        WriteLine($"{nameof(RetryWithTimeout)} - onRetryInner #{i} due to exception '{(e.InnerException ?? e).Message}'");
        return Task.CompletedTask;
    });

    var retryPolicy = Policy
        .Handle<Exception>()
        .RetryAsync(retryCount,onRetry ?? onRetryInner);

    var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromMilliseconds(timeoutDelay));

    var policyWrap = timeoutPolicy.WrapAsync(retryPolicy);

    return await policyWrap.ExecuteAsync(
                    async (ct) => await func(ct),CancellationToken.None);
}

=>重试API调用，直到出现超时

谢谢@Peter Csala！

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