Polly：如何结合 TimeoutPolicy 和 RetryPolicy 来请求 Func
Polly: how to combine TimeoutPolicy and RetryPolicy to request a Func
我正在尝试将 TimeoutPolicy 和 RetryPolicy 结合起来用于 Func 中完成的 API 调用，但我没有找到实现此目的的方法.
如果我只使用 RetryPolicy，它工作正常。
我有一个 GetRequest 方法调用 HttpClient 和 return 数据：
async Task<Data> GetRequest(string api, int id)
{
var httpClient = new HttpClient();
var response = await httpClient.GetAsync($"{api}{id}");
var rawResponse = await response.Content.ReadAsStringAsync();
return JsonConvert.DeserializeObject<Data>(rawResponse);
}
我还有 Func 将嵌入对此方法的调用：
var func = new Func<Task<Data>>(() => GetRequest(api, i));
我这样调用服务：
Results.Add(await _networkService.RetryWithoutTimeout<Data>(func, 3, OnRetry));
这个RetryWithoutTimeout方法是这样的：
async Task<T> RetryWithoutTimeout<T>(Func<Task<T>> func, int retryCount = 1, Func<Exception, int, Task> onRetry = null)
{
var onRetryInner = new Func<Exception, int, Task>((e, i) =>
{
return Task.Factory.StartNew(() => {
#if DEBUG
System.Diagnostics.Debug.WriteLine($"Retry #{i} due to exception '{(e.InnerException ?? e).Message}'");
#endif
});
});
return await Policy.Handle<Exception>()
.RetryAsync(retryCount, onRetry ?? onRetryInner)
.ExecuteAsync<T>(func);
}
我已经更新此代码以使用 TimeoutPolicy，以及新的 RetryWithTimeout 方法：
async Task<T> RetryWithTimeout<T>(Func<Task<T>> func, int retryCount = 1, Func<Exception, int, Task> onRetry = null, int timeoutDelay = 30)
{
var onRetryInner = new Func<Exception, int, Task>((e, i) =>
{
return Task.Factory.StartNew(() => {
#if DEBUG
System.Diagnostics.Debug.WriteLine($"Retry #{i} due to exception '{(e.InnerException ?? e).Message}'");
#endif
});
});
var retryPolicy = Policy
.Handle<Exception>()
.RetryAsync(retryCount, onRetry ?? onRetryInner);
var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromSeconds(timeoutDelay));
var policyWrap = timeoutPolicy.WrapAsync((IAsyncPolicy)retryPolicy);
return await policyWrap.ExecuteAsync(
async ct => await Task.Run(func),
CancellationToken.None
);
}
但是我不知道如何管理 GetRequest() 方法：我所有的测试都失败了...
编辑：
我根据@Peter Csala 的评论创建了一个示例。
所以首先，我刚刚更新了重试次数以检查retryPolicy是否正确应用：
private const int TimeoutInMilliseconds = 2500;
private const int MaxRetries = 3;
private static int _times;
static async Task Main(string[] args)
{
try
{
await RetryWithTimeout(TestStrategy, MaxRetries);
}
catch (Exception ex)
{
WriteLine($"{nameof(Main)} - Exception - Failed due to: {ex.Message}");
}
Console.ReadKey();
}
private static async Task<string> TestStrategy(CancellationToken ct)
{
WriteLine($"{nameof(TestStrategy)} has been called for the {_times++}th times.");
await Task.Delay(TimeoutInMilliseconds * 2, ct);
return "Finished";
}
internal static async Task<T> RetryWithTimeout<T>(Func<CancellationToken, Task<T>> func, int retryCount = 1, Func<Exception, int, Task> onRetry = null, int timeoutDelay = TimeoutInMilliseconds)
{
WriteLine($"NetworkService - {nameof(RetryWithTimeout)}");
var onRetryInner = new Func<Exception, int, Task>((e, i) =>
{
WriteLine($"NetworkService - {nameof(RetryWithTimeout)} #{i} due to exception '{(e.InnerException ?? e).Message}'");
return Task.CompletedTask;
});
var retryPolicy = Policy
.Handle<Exception>()
.RetryAsync(retryCount, onRetry ?? onRetryInner);
var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromMilliseconds(timeoutDelay));
var policyWrap = Policy.WrapAsync(retryPolicy, timeoutPolicy); //Important part #1
return await policyWrap.ExecuteAsync(
async ct => await func(ct), //Important part #2
CancellationToken.None);
}
关于日志，是这样的：
NetworkService - RetryWithTimeout
TestStrategy has been called for the 0th times.
NetworkService - RetryWithTimeout - Retry #1 due to exception 'A task was canceled.'
TestStrategy has been called for the 1th times.
NetworkService - RetryWithTimeout - Retry #2 due to exception 'A task was canceled.'
TestStrategy has been called for the 2th times.
NetworkService - RetryWithTimeout - Retry #3 due to exception 'A task was canceled.'
TestStrategy has been called for the 3th times.
Main - TimeoutRejectedException - Failed due to: The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.
然后，我更改了 policyWrap 因为我需要全局超时：
private static async Task<string> TestStrategy(CancellationToken ct)
{
WriteLine($"{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，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.
在那之后，我实现了一个调用 API 的方法，其中一些 Exceptions 更接近我的需要：
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，我可以在每个 API 调用中重复使用该方法。这个方法将是这样的：
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($"No success status code {response.StatusCode}");
}
var rawResponse = await response.Content.ReadAsStringAsync();
return JsonConvert.DeserializeObject<T>(rawResponse);
}
但是为此，我必须同时通过 CancellationToken 和 Api Uri 通过 RetryWithTimeout 我不知道如何来管理这个。
我尝试通过类似以下方式更改 RetryWithTimeout 的签名：
internal static async Task<T> RetryWithTimeout<T>(Func<Uri, CancellationToken, Task<T>> func, int retryCount = 1, Func<Exception, int, Task> onRetry = null, int timeoutDelay = TimeoutInMilliseconds)
但我找不到如何管理 Func...
你有什么想法或解释吗？
您需要将 CancellationToken 传递给 to-be-cancelled（由于超时）函数。
那么，假设您有以下简化方法：
private const int TimeoutInMilliseconds = 1000;
private static int _times;
private static async Task<string> TestStrategy(CancellationToken ct)
{
Console.WriteLine($"{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, int, Task>((e, i) =>
{
Console.WriteLine($"Retry #{i} due to exception '{(e.InnerException ?? e).Message}'");
return Task.CompletedTask;
});
var retryPolicy = Policy
.Handle<Exception>()
.RetryAsync(retryCount, onRetry ?? onRetryInner);
var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromMilliseconds(timeoutDelay));
var policyWrap = Policy.WrapAsync(retryPolicy, timeoutPolicy); //Important part #1
return await policyWrap.ExecuteAsync(
async ct => await func(ct), //Important part #2
CancellationToken.None);
}
重要部分 #1 - 重试是外部策略，超时是内部策略
重要部分 #2 - 由于超时
，CancellationToken 被传递给 to-be-cancelled 函数
下面的用法
static async Task Main(string[] args)
{
try
{
await RetryWithTimeout(TestStrategy);
}
catch (Exception ex)
{
Console.WriteLine($"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，在重试开始之前有第 0 次尝试。
我终于找到了一个可行的解决方案，这个解决方案已由@Peter Csala 完成。
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, Func<Exception, int, 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($"{nameof(ProcessGetRequest)} - Success");
return JsonConvert.DeserializeObject<T>(rawResponse);
}
internal static async Task<T> RetryWithTimeout<T>(Func<CancellationToken, Task<T>> func, Uri uri, int retryCount = 1, Func<Exception, int, Task> onRetry = null, int timeoutDelay = TimeoutInMilliseconds)
{
WriteLine($"{nameof(RetryWithTimeout)}");
var onRetryInner = new Func<Exception, int, Task>((e, i) =>
{
WriteLine($"{nameof(RetryWithTimeout)} - onRetryInner #{i} due to exception '{(e.InnerException ?? e).Message}'");
return Task.CompletedTask;
});
var retryPolicy = Policy
.Handle<Exception>()
.RetryAsync(retryCount, onRetry ?? onRetryInner);
var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromMilliseconds(timeoutDelay));
var policyWrap = timeoutPolicy.WrapAsync(retryPolicy);
return await policyWrap.ExecuteAsync(
async (ct) => await func(ct),
CancellationToken.None);
}
我得到这些结果：
GetCountriesWithRetry
GetAndRetry
RetryWithTimeout
ProcessGetRequest
ProcessGetRequest - !response.IsSuccessStatusCode
RetryWithTimeout - onRetryInner #1 due to exception 'No success status code InternalServerError'
ProcessGetRequest
ProcessGetRequest - !response.IsSuccessStatusCode
RetryWithTimeout - onRetryInner #2 due to exception 'No success status code InternalServerError'
LoadCountriesWithRetry - TimeoutRejectedException : The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.
=> 重试 API 调用，直到超时
谢谢@Peter Csala！
我正在尝试将 TimeoutPolicy 和 RetryPolicy 结合起来用于 Func 中完成的 API 调用，但我没有找到实现此目的的方法.
如果我只使用 RetryPolicy，它工作正常。
我有一个 GetRequest 方法调用 HttpClient 和 return 数据：
async Task<Data> GetRequest(string api, int id)
{
var httpClient = new HttpClient();
var response = await httpClient.GetAsync($"{api}{id}");
var rawResponse = await response.Content.ReadAsStringAsync();
return JsonConvert.DeserializeObject<Data>(rawResponse);
}
我还有 Func 将嵌入对此方法的调用：
var func = new Func<Task<Data>>(() => GetRequest(api, i));
我这样调用服务：
Results.Add(await _networkService.RetryWithoutTimeout<Data>(func, 3, OnRetry));
这个RetryWithoutTimeout方法是这样的：
async Task<T> RetryWithoutTimeout<T>(Func<Task<T>> func, int retryCount = 1, Func<Exception, int, Task> onRetry = null)
{
var onRetryInner = new Func<Exception, int, Task>((e, i) =>
{
return Task.Factory.StartNew(() => {
#if DEBUG
System.Diagnostics.Debug.WriteLine($"Retry #{i} due to exception '{(e.InnerException ?? e).Message}'");
#endif
});
});
return await Policy.Handle<Exception>()
.RetryAsync(retryCount, onRetry ?? onRetryInner)
.ExecuteAsync<T>(func);
}
我已经更新此代码以使用 TimeoutPolicy，以及新的 RetryWithTimeout 方法：
async Task<T> RetryWithTimeout<T>(Func<Task<T>> func, int retryCount = 1, Func<Exception, int, Task> onRetry = null, int timeoutDelay = 30)
{
var onRetryInner = new Func<Exception, int, Task>((e, i) =>
{
return Task.Factory.StartNew(() => {
#if DEBUG
System.Diagnostics.Debug.WriteLine($"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
);
}
但是我不知道如何管理 GetRequest() 方法：我所有的测试都失败了...
编辑： 我根据@Peter Csala 的评论创建了一个示例。
所以首先，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 retryCount = 1, Func<Exception, int, Task> onRetry = null, int timeoutDelay = TimeoutInMilliseconds)
{
WriteLine($"NetworkService - {nameof(RetryWithTimeout)}");
var onRetryInner = new Func<Exception, int, Task>((e, i) =>
{
WriteLine($"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，是这样的：
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，我更改了 policyWrap 因为我需要全局超时：
private static async Task<string> TestStrategy(CancellationToken ct)
{
WriteLine($"{nameof(TestStrategy)} has been called for the {_times++}th times.");
await Task.Delay(1500, ct);
throw new Exception("simulate Exception");
}
var policyWrap = timeoutPolicy.WrapAsync(retryPolicy);
关于日志，也是正确的：
TestStrategy has been called for the 0th times.
NetworkService - RetryWithTimeout #1 due to exception 'simulate Exception'
TestStrategy has been called for the 1th times.
NetworkService - RetryWithTimeout #2 due to exception 'A task was canceled.'
Main - TimeoutRejectedException - Failed due to: The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.
在那之后，我实现了一个调用 API 的方法，其中一些 Exceptions 更接近我的需要：
static async Task Main(string[] args)
{
try
{
await RetryWithTimeout(GetClientAsync, MaxRetries);
}
catch (TimeoutRejectedException trEx)
{
WriteLine($"{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($"{nameof(GetClientAsync)} - other exception: {ex.Message}");
throw ex;
}
}
日志仍然正确：
NetworkService - RetryWithTimeout
GetClientAsync has been called for the 0th times.
GetClientAsync - !response.IsSuccessStatusCode
GetClientAsync - WebException: No success status code InternalServerError
NetworkService - RetryWithTimeout #1 due to exception 'No success status code InternalServerError'
GetClientAsync has been called for the 1th times.
GetClientAsync - !response.IsSuccessStatusCode
GetClientAsync - WebException: No success status code InternalServerError
NetworkService - RetryWithTimeout #2 due to exception 'No success status code InternalServerError'
GetClientAsync has been called for the 2th times.
GetClientAsync - !response.IsSuccessStatusCode
GetClientAsync - WebException: No success status code InternalServerError
NetworkService - RetryWithTimeout #3 due to exception 'No success status code InternalServerError'
GetClientAsync has been called for the 3th times.
GetClientAsync - other exception: The operation was canceled.
Main - TimeoutRejectedException - Failed due to: The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.
最后，我希望能够调用一个“通用”方法，我可以在每个 API 调用中重复使用该方法。这个方法将是这样的：
static async Task<T> ProcessGetRequest<T>(Uri uri, CancellationToken ct)
{
WriteLine("ApiService - ProcessGetRequest()");
HttpClient _client = new HttpClient();
var response = await _client.GetAsync(uri);
if (!response.IsSuccessStatusCode)
{
WriteLine("ApiService - ProcessGetRequest() - !response.IsSuccessStatusCode");
throw new WebException($"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 和 Api Uri 通过 RetryWithTimeout 我不知道如何来管理这个。
我尝试通过类似以下方式更改 RetryWithTimeout 的签名：
internal static async Task<T> RetryWithTimeout<T>(Func<Uri, CancellationToken, Task<T>> func, int retryCount = 1, Func<Exception, int, Task> onRetry = null, int timeoutDelay = TimeoutInMilliseconds)
但我找不到如何管理 Func...
你有什么想法或解释吗？
您需要将 CancellationToken 传递给 to-be-cancelled（由于超时）函数。
那么，假设您有以下简化方法：
private const int TimeoutInMilliseconds = 1000;
private static int _times;
private static async Task<string> TestStrategy(CancellationToken ct)
{
Console.WriteLine($"{nameof(TestStrategy)} has been called for the {_times++}th times.");
await Task.Delay(TimeoutInMilliseconds * 2, ct);
return "Finished";
}
因此，您的 RetryWithTimeout 可以这样调整/修改：
static async Task<T> RetryWithTimeout<T>(Func<CancellationToken, Task<T>> func, int retryCount = 1, Func<Exception, int, Task> onRetry = null, int timeoutDelay = TimeoutInMilliseconds)
{
var onRetryInner = new Func<Exception, int, Task>((e, i) =>
{
Console.WriteLine($"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);
}
重要部分 #1 - 重试是外部策略，超时是内部策略
重要部分 #2 - 由于超时
下面的用法
static async Task Main(string[] args)
{
try
{
await RetryWithTimeout(TestStrategy);
}
catch (Exception ex)
{
Console.WriteLine($"Failed due to: {ex.Message}");
}
Console.ReadKey();
}
将产生以下输出：
TestStrategy has been called for the 0th times.
Retry #1 due to exception 'A task was canceled.'
TestStrategy has been called for the 1th times.
Failed due to: The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.
请记住，在重试开始之前有第 0 次尝试。
我终于找到了一个可行的解决方案，这个解决方案已由@Peter Csala 完成。
private const int TimeoutInMilliseconds = 2500;
private const int MaxRetries = 3;
private static Uri apiUri = new Uri("https://api/param");
private static int _times;
public static Country[] Countries
{
get;
set;
}
static async Task Main(string[] args)
{
try
{
await LoadCountriesWithRetry(false);
}
catch (Exception ex)
{
WriteLine($"{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($"{nameof(GetCountriesWithRetry)}");
var response = await GetAndRetry<CountriesResponse>(uri, MaxRetries);
return response?.Countries;
}
static Func<CancellationToken, Task<T>> IssueRequest<T>(Uri uri) => ct => ProcessGetRequest<T>(ct, uri);
public static async Task<T> GetAndRetry<T>(Uri uri, int retryCount, Func<Exception, int, Task> onRetry = null)
where T : class
{
WriteLine($"{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, Task<T>> func, Uri uri, int retryCount = 1, Func<Exception, int, Task> onRetry = null, int timeoutDelay = TimeoutInMilliseconds)
{
WriteLine($"{nameof(RetryWithTimeout)}");
var onRetryInner = new Func<Exception, int, Task>((e, i) =>
{
WriteLine($"{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);
}
我得到这些结果：
GetCountriesWithRetry
GetAndRetry
RetryWithTimeout
ProcessGetRequest
ProcessGetRequest - !response.IsSuccessStatusCode
RetryWithTimeout - onRetryInner #1 due to exception 'No success status code InternalServerError'
ProcessGetRequest
ProcessGetRequest - !response.IsSuccessStatusCode
RetryWithTimeout - onRetryInner #2 due to exception 'No success status code InternalServerError'
LoadCountriesWithRetry - TimeoutRejectedException : The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.
=> 重试 API 调用，直到超时
谢谢@Peter Csala！