【编辑推荐】.NETCore微服务之路：弹性和瞬态故障处理库Polly的

public static void Retry(){    var tick = 0;    const int maxRetry = 6;    var retry = Policy.Handle().Retry(maxRetry);    try    {        retry.Execute(() =>        {            Console.WriteLine($@"try {++tick}");            if (tick >= 1)                // 出现故障，开始重试Execute                throw new Exception("throw the exception");        });    }    catch (Exception ex)    {        Console.WriteLine(@"exception : " + ex.Message);    }}

try 1try 2try 3try 4try 5try 6try 7exception : throw the exception

public static void Fallback(){    Policy.Handle().Fallback(() => { Console.WriteLine(@"error occured"); })        .Execute(() =>        {            Console.WriteLine(@"try");            // 出现故障，进行降级处理Fallback            throw new ArgumentException(@"throw the exception");        });}

tryerror occured

public static void Cache(){    const int ttl = 60;    var policy = Policy.Cache(new MemoryCacheProvider(new MemoryCache(new MemoryCacheOptions())), TimeSpan.FromSeconds(ttl));    var context = new Context(operationKey: "cache_key");    for (var i = 0; i < 3; i++)    {        var cache = policy.Execute(_ =>        {            Console.WriteLine(@"get value");            return 3;        }, context);        Console.WriteLine(cache);    }}

get value333

public static void CircuitBreaker(){    var tick = 0;    const int interval = 10;    const int maxRetry = 6;    var circuitBreaker = Policy.Handle().CircuitBreaker(maxRetry, TimeSpan.FromSeconds(interval));    while (true)    {        try        {            circuitBreaker.Execute(() =>            {                Console.WriteLine($@"try {++tick}");                throw new Exception("throw the exception");            });        }        catch (Exception ex)        {            Console.WriteLine(@"exception : " + ex.Message);            // 当重试次数达到断路器指定的次数时，Polly会抛出The circuit is now open and is not allowing calls. 断路器已打开，不允许访问            // 为了演示，故意将下面语句写上，可退出while循环            // 实际环境中视情况，断开绝不等于退出，或许20-30秒后，服务维护后变得可用了            if (ex.Message.Contains("The circuit is now open and is not allowing calls"))            {                break;            }        }        Thread.Sleep(300);    }}

try 1exception : throw the exceptiontry 2exception : throw the exceptiontry 3exception : throw the exceptiontry 4exception : throw the exceptiontry 5exception : throw the exceptiontry 6exception : throw the exceptionexception : The circuit is now open and is not allowing calls.

public static void Timeout(){    const int timeoutSecond = 3;    try    {        Policy.Wrap(            Policy.Timeout(timeoutSecond, TimeoutStrategy.Pessimistic),            Policy.Handle().Fallback(() => { })        ).Execute(() =>        {            Console.WriteLine(@"try");            Thread.Sleep(5000);        });    }    catch (Exception ex)    {        // 当超时时间到，会抛出The delegate executed through TimeoutPolicy did not complete within the timeout.        // 委托执行未在指定时间内完成        Console.WriteLine($@"exception : {ex.GetType()} : {ex.Message}");    }}

以上策略很好理解，组合一个超时和回退的策略组合，当超时已到，执行回退操作，执行结果如下：

tryexception : Polly.Timeout.TimeoutRejectedException : The delegate executed through TimeoutPolicy did not complete within the timeout.

总结