public static void OutputState()
{
ConsoleHelper.WriteInColor(String.Format(" Good endpoint: requested {0:00}, ", goodRequestsMade), ConsoleColor.White);
ConsoleHelper.WriteInColor(String.Format("succeeded {0:00}, ", goodRequestsSucceeded), ConsoleColor.Green);
ConsoleHelper.WriteInColor(String.Format("pending {0:00}, ", goodRequestsMade - goodRequestsSucceeded - goodRequestsFailed), ConsoleColor.Yellow);
ConsoleHelper.WriteLineInColor(String.Format("failed {0:00}.", goodRequestsFailed), ConsoleColor.Red);
ConsoleHelper.WriteInColor(String.Format("Faulting endpoint: requested {0:00}, ", faultingRequestsMade), ConsoleColor.White);
ConsoleHelper.WriteInColor(String.Format("succeeded {0:00}, ", faultingRequestsSucceeded), ConsoleColor.Green);
ConsoleHelper.WriteInColor(String.Format("pending {0:00}, ", faultingRequestsMade - faultingRequestsSucceeded - faultingRequestsFailed), ConsoleColor.Yellow);
ConsoleHelper.WriteLineInColor(String.Format("failed {0:00}.", faultingRequestsFailed), ConsoleColor.Red);
Console.WriteLine();
}
public static void Execute()
{
Console.WriteLine(MethodBase.GetCurrentMethod().DeclaringType.Name);
Console.WriteLine("=======");
// Let's call a web api service to make repeated requests to a server.
// The service is programmed to fail after 3 requests in 5 seconds.
var client = new WebClient();
int eventualSuccesses = 0;
int retries = 0;
int eventualFailuresDueToCircuitBreaking = 0;
int eventualFailuresForOtherReasons = 0;
Stopwatch watch = null;
// Define our waitAndRetry policy: keep retrying with 200ms gaps.
RetryPolicy waitAndRetryPolicy = Policy
.Handle <Exception>(e => !(e is BrokenCircuitException)) // Exception filtering! We don't retry if the inner circuit-breaker judges the underlying system is out of commission!
.WaitAndRetryForever(
attempt => TimeSpan.FromMilliseconds(200),
(exception, calculatedWaitDuration) =>
{
ConsoleHelper.WriteLineInColor(".Log,then retry: " + exception.Message, ConsoleColor.Yellow);
retries++;
});
// Define our CircuitBreaker policy: Break if the action fails 4 times in a row.
CircuitBreakerPolicy circuitBreakerPolicy = Policy
.Handle <Exception>()
.CircuitBreaker(
exceptionsAllowedBeforeBreaking: 4,
durationOfBreak: TimeSpan.FromSeconds(3),
onBreak: (ex, breakDelay) =>
{
ConsoleHelper.WriteLineInColor(".Breaker logging: Breaking the circuit for " + breakDelay.TotalMilliseconds + "ms!", ConsoleColor.Magenta);
ConsoleHelper.WriteLineInColor("..due to: " + ex.Message, ConsoleColor.Magenta);
},
onReset: () => ConsoleHelper.WriteLineInColor(".Breaker logging: Call ok! Closed the circuit again!", ConsoleColor.Magenta),
onHalfOpen: () => ConsoleHelper.WriteLineInColor(".Breaker logging: Half-open: Next call is a trial!", ConsoleColor.Magenta)
);
// Define a fallback policy: provide a nice substitute message to the user, if we found the circuit was broken.
FallbackPolicy <String> fallbackForCircuitBreaker = Policy <String>
.Handle <BrokenCircuitException>()
.Fallback(
fallbackValue: /* Demonstrates fallback value syntax */ "Please try again later [Fallback for broken circuit]",
onFallback: b =>
{
watch.Stop();
ConsoleHelper.WriteInColor("Fallback catches failed with: " + b.Exception.Message, ConsoleColor.Red);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Red);
eventualFailuresDueToCircuitBreaking++;
}
);
// Define a fallback policy: provide a substitute string to the user, for any exception.
FallbackPolicy <String> fallbackForAnyException = Policy <String>
.Handle <Exception>()
.Fallback(
fallbackAction: /* Demonstrates fallback action/func syntax */ () => { return("Please try again later [Fallback for any exception]"); },
onFallback: e =>
{
watch.Stop();
ConsoleHelper.WriteInColor("Fallback catches eventually failed with: " + e.Exception.Message, ConsoleColor.Red);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Red);
eventualFailuresForOtherReasons++;
}
);
// As demo07: we combine the waitAndRetryPolicy and circuitBreakerPolicy into a PolicyWrap, using the *static* Policy.Wrap syntax.
PolicyWrap myResilienceStrategy = Policy.Wrap(waitAndRetryPolicy, circuitBreakerPolicy);
// Added in demo08: we wrap the two fallback policies onto the front of the existing wrap too. Demonstrates the *instance* wrap syntax. And the fact that the PolicyWrap myResilienceStrategy from above is just another Policy, which can be onward-wrapped too.
// With this pattern, you can build an overall resilience strategy programmatically, reusing some common parts (eg PolicyWrap myResilienceStrategy) but varying other parts (eg Fallback) individually for different calls.
PolicyWrap <String> policyWrap = fallbackForAnyException.Wrap(fallbackForCircuitBreaker.Wrap(myResilienceStrategy));
// For info: Equivalent to: PolicyWrap<String> policyWrap = Policy.Wrap(fallbackForAnyException, fallbackForCircuitBreaker, waitAndRetryPolicy, circuitBreakerPolicy);
int i = 0;
// Do the following until a key is pressed
while (!Console.KeyAvailable)
{
i++;
watch = new Stopwatch();
watch.Start();
try
{
// Manage the call according to the whole policy wrap.
string msg = policyWrap.Execute(() => client.DownloadString(Configuration.WEB_API_ROOT + "/api/values/" + i));
watch.Stop();
// Display the response message on the console
ConsoleHelper.WriteInColor("Response : " + msg, ConsoleColor.Green);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Green);
eventualSuccesses++;
}
catch (Exception e) // try-catch not needed, now that we have a Fallback.Handle<Exception>. It's only been left in to *demonstrate* it should never get hit.
{
throw new InvalidOperationException("Should never arrive here. Use of fallbackForAnyException should have provided nice fallback value for any exceptions.", e);
}
// Wait half second
Thread.Sleep(500);
}
Console.WriteLine("");
Console.WriteLine("Total requests made : " + i);
Console.WriteLine("Requests which eventually succeeded : " + eventualSuccesses);
Console.WriteLine("Retries made to help achieve success : " + retries);
Console.WriteLine("Requests failed early by broken circuit : " + eventualFailuresDueToCircuitBreaking);
Console.WriteLine("Requests which failed after longer delay: " + eventualFailuresForOtherReasons);
}
public static async Task ExecuteAsync(CancellationToken cancellationToken)
{
Console.WriteLine(typeof(AsyncDemo06_WaitAndRetryNestingCircuitBreaker).Name);
Console.WriteLine("=======");
// Let's call a web api service to make repeated requests to a server.
// The service is programmed to fail after 3 requests in 5 seconds.
var client = new HttpClient();
int eventualSuccesses = 0;
int retries = 0;
int eventualFailuresDueToCircuitBreaking = 0;
int eventualFailuresForOtherReasons = 0;
// Define our waitAndRetry policy: keep retrying with 200ms gaps.
var waitAndRetryPolicy = Policy
.Handle <Exception>(e => !(e is BrokenCircuitException)) // Exception filtering! We don't retry if the inner circuit-breaker judges the underlying system is out of commission!
.WaitAndRetryForeverAsync(
attempt => TimeSpan.FromMilliseconds(200),
(exception, calculatedWaitDuration) =>
{
// This is your new exception handler!
// Tell the user what they've won!
ConsoleHelper.WriteLineInColor(".Log,then retry: " + exception.Message, ConsoleColor.Yellow);
retries++;
});
// Define our CircuitBreaker policy: Break if the action fails 4 times in a row.
var circuitBreakerPolicy = Policy
.Handle <Exception>()
.CircuitBreakerAsync(
exceptionsAllowedBeforeBreaking: 4,
durationOfBreak: TimeSpan.FromSeconds(3),
onBreak: (ex, breakDelay) =>
{
ConsoleHelper.WriteLineInColor(".Breaker logging: Breaking the circuit for " + breakDelay.TotalMilliseconds + "ms!", ConsoleColor.Magenta);
ConsoleHelper.WriteLineInColor("..due to: " + ex.Message, ConsoleColor.Magenta);
},
onReset: () => ConsoleHelper.WriteLineInColor(".Breaker logging: Call ok! Closed the circuit again!", ConsoleColor.Magenta),
onHalfOpen: () => ConsoleHelper.WriteLineInColor(".Breaker logging: Half-open: Next call is a trial!", ConsoleColor.Magenta)
);
int i = 0;
// Do the following until a key is pressed
while (!Console.KeyAvailable && !cancellationToken.IsCancellationRequested)
{
i++;
Stopwatch watch = new Stopwatch();
watch.Start();
try
{
// Retry the following call according to the policy - 3 times.
await waitAndRetryPolicy.ExecuteAsync(async token =>
{
// This code is executed within the waitAndRetryPolicy
string msg = await circuitBreakerPolicy.ExecuteAsync <String>(() => // Note how we can also Execute() a Func<TResult> and pass back the value.
{
// This code is executed within the circuitBreakerPolicy
// Make a request and get a response
return(client.GetStringAsync(Configuration.WEB_API_ROOT + "/api/values/" + i));
});
watch.Stop();
// Display the response message on the console
ConsoleHelper.WriteInColor("Response : " + msg, ConsoleColor.Green);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Green);
eventualSuccesses++;
}, cancellationToken);
}
catch (BrokenCircuitException b)
{
watch.Stop();
ConsoleHelper.WriteInColor("Request " + i + " failed with: " + b.GetType().Name, ConsoleColor.Red);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Red);
eventualFailuresDueToCircuitBreaking++;
}
catch (Exception e)
{
watch.Stop();
ConsoleHelper.WriteInColor("Request " + i + " eventually failed with: " + e.Message, ConsoleColor.Red);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Red);
eventualFailuresForOtherReasons++;
}
// Wait half second
await Task.Delay(TimeSpan.FromSeconds(0.5), cancellationToken);
}
Console.WriteLine("");
Console.WriteLine("Total requests made : " + i);
Console.WriteLine("Requests which eventually succeeded : " + eventualSuccesses);
Console.WriteLine("Retries made to help achieve success : " + retries);
Console.WriteLine("Requests failed early by broken circuit : " + eventualFailuresDueToCircuitBreaking);
Console.WriteLine("Requests which failed after longer delay: " + eventualFailuresForOtherReasons);
}
public static void Execute()
{
Console.WriteLine(MethodBase.GetCurrentMethod().DeclaringType.Name);
Console.WriteLine("=======");
// Let's call a web api service to make repeated requests to a server.
// The service is programmed to fail after 3 requests in 5 seconds.
var client = new WebClient();
int eventualSuccesses = 0;
int retries = 0;
int eventualFailuresDueToCircuitBreaking = 0;
int eventualFailuresForOtherReasons = 0;
// Define our waitAndRetry policy: keep retrying with 200ms gaps.
RetryPolicy waitAndRetryPolicy = Policy
.Handle <Exception>(e => !(e is BrokenCircuitException)) // Exception filtering! We don't retry if the inner circuit-breaker judges the underlying system is out of commission!
.WaitAndRetryForever(
attempt => TimeSpan.FromMilliseconds(200),
(exception, calculatedWaitDuration) =>
{
// This is your new exception handler!
// Tell the user what they've won!
ConsoleHelper.WriteLineInColor(".Log,then retry: " + exception.Message, ConsoleColor.Yellow);
retries++;
});
// Define our CircuitBreaker policy: Break if the action fails 4 times in a row.
CircuitBreakerPolicy circuitBreakerPolicy = Policy
.Handle <Exception>()
.CircuitBreaker(
exceptionsAllowedBeforeBreaking: 4,
durationOfBreak: TimeSpan.FromSeconds(3),
onBreak: (ex, breakDelay) =>
{
ConsoleHelper.WriteLineInColor(".Breaker logging: Breaking the circuit for " + breakDelay.TotalMilliseconds + "ms!", ConsoleColor.Magenta);
ConsoleHelper.WriteLineInColor("..due to: " + ex.Message, ConsoleColor.Magenta);
},
onReset: () => ConsoleHelper.WriteLineInColor(".Breaker logging: Call ok! Closed the circuit again!", ConsoleColor.Magenta),
onHalfOpen: () => ConsoleHelper.WriteLineInColor(".Breaker logging: Half-open: Next call is a trial!", ConsoleColor.Magenta)
);
// New for demo07: combine the waitAndRetryPolicy and circuitBreakerPolicy into a PolicyWrap.
PolicyWrap policyWrap = Policy.Wrap(waitAndRetryPolicy, circuitBreakerPolicy);
int i = 0;
// Do the following until a key is pressed
while (!Console.KeyAvailable)
{
i++;
Stopwatch watch = new Stopwatch();
watch.Start();
try
{
// Retry the following call according to the policy wrap
string msg = policyWrap.Execute <String>(() =>
{
// This code is executed through both policies in the wrap: WaitAndRetry outer, then CircuitBreaker inner. Demo 06 shows a broken-out version of what this is equivalent to.
return(client.DownloadString(Configuration.WEB_API_ROOT + "/api/values/" + i));
});
// Without the extra comments in the anonymous method { } above, it could even be as concise as this:
// string msg = policyWrap.Execute(() => client.DownloadString(Configuration.WEB_API_ROOT + "/api/values/" + i));
watch.Stop();
// Display the response message on the console
ConsoleHelper.WriteInColor("Response : " + msg, ConsoleColor.Green);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Green);
eventualSuccesses++;
}
catch (BrokenCircuitException b)
{
watch.Stop();
ConsoleHelper.WriteInColor("Request " + i + " failed with: " + b.GetType().Name, ConsoleColor.Red);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Red);
eventualFailuresDueToCircuitBreaking++;
}
catch (Exception e)
{
watch.Stop();
ConsoleHelper.WriteInColor("Request " + i + " eventually failed with: " + e.Message, ConsoleColor.Red);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Red);
eventualFailuresForOtherReasons++;
}
// Wait half second
Thread.Sleep(500);
}
Console.WriteLine("");
Console.WriteLine("Total requests made : " + i);
Console.WriteLine("Requests which eventually succeeded : " + eventualSuccesses);
Console.WriteLine("Retries made to help achieve success : " + retries);
Console.WriteLine("Requests failed early by broken circuit : " + eventualFailuresDueToCircuitBreaking);
Console.WriteLine("Requests which failed after longer delay: " + eventualFailuresForOtherReasons);
}
public static async Task ExecuteAsync(CancellationToken cancellationToken)
{
Console.WriteLine(typeof(AsyncDemo09_Wrap_Fallback_Timeout_WaitAndRetry).Name);
Console.WriteLine("=======");
// Let's call a web api service to make repeated requests to a server.
// The service is programmed to fail after 3 requests in 5 seconds.
var client = new HttpClient();
int eventualSuccesses = 0;
int retries = 0;
int eventualFailuresDueToTimeout = 0;
int eventualFailuresForOtherReasons = 0;
Stopwatch watch = null;
// Define our timeout policy: time out after 2 seconds. We will use the pessimistic timeout strategy, which forces a timeout - even when the underlying delegate doesn't support it.
var timeoutPolicy = Policy
.TimeoutAsync(TimeSpan.FromSeconds(2), TimeoutStrategy.Pessimistic);
// Define our waitAndRetry policy: keep retrying with 4 second gaps. This is (intentionally) too long: to demonstrate that the timeout policy will time out on this before waiting for the retry.
var waitAndRetryPolicy = Policy
.Handle <Exception>() // Exception filtering! We don't retry if the inner circuit-breaker judges the underlying system is out of commission!
.WaitAndRetryForeverAsync(
attempt => TimeSpan.FromSeconds(4),
(exception, calculatedWaitDuration) =>
{
ConsoleHelper.WriteLineInColor(".Log,then retry: " + exception.Message, ConsoleColor.Yellow);
retries++;
});
// Define a fallback policy: provide a nice substitute message to the user, if we found the call was rejected due to the timeout policy.
FallbackPolicy <String> fallbackForTimeout = Policy <String>
.Handle <TimeoutRejectedException>()
.FallbackAsync(
fallbackValue: /* Demonstrates fallback value syntax */ "Please try again later [Fallback for timeout]",
onFallbackAsync: async b =>
{
watch.Stop();
ConsoleHelper.WriteInColor("Fallback catches failed with: " + b.Exception.Message, ConsoleColor.Red);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Red);
eventualFailuresDueToTimeout++;
}
);
// Define a fallback policy: provide a substitute string to the user, for any exception.
FallbackPolicy <String> fallbackForAnyException = Policy <String>
.Handle <Exception>()
.FallbackAsync(
fallbackAction: /* Demonstrates fallback action/func syntax */ async ct =>
{
/* do something else async if desired */
return("Please try again later [Fallback for any exception]");
},
onFallbackAsync: async e =>
{
watch.Stop();
ConsoleHelper.WriteInColor("Fallback catches eventually failed with: " + e.Exception.Message, ConsoleColor.Red);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Red);
eventualFailuresForOtherReasons++;
}
);
// Compared to previous demo08: here we use *instance* wrap syntax, to wrap all in one go.
PolicyWrap <String> policyWrap = fallbackForAnyException.WrapAsync(fallbackForTimeout).WrapAsync(timeoutPolicy).WrapAsync(waitAndRetryPolicy).WrapAsync(waitAndRetryPolicy);
int i = 0;
while (!Console.KeyAvailable && !cancellationToken.IsCancellationRequested)
{
i++;
watch = new Stopwatch();
watch.Start();
try
{
// Manage the call according to the whole policy wrap
string msg = await policyWrap.ExecuteAsync(ct => client.GetStringAsync(Configuration.WEB_API_ROOT + "/api/values/" + i), cancellationToken);
watch.Stop();
// Display the response message on the console
ConsoleHelper.WriteInColor("Response : " + msg, ConsoleColor.Green);
ConsoleHelper.WriteLineInColor(" (after " + watch.ElapsedMilliseconds + "ms)", ConsoleColor.Green);
eventualSuccesses++;
}
catch (Exception e) // try-catch not needed, now that we have a Fallback.Handle<Exception>. It's only been left in to *demonstrate* it should never get hit.
{
throw new InvalidOperationException("Should never arrive here. Use of fallbackForAnyException should have provided nice fallback value for any exceptions.", e);
}
// Wait half second
await Task.Delay(TimeSpan.FromSeconds(0.5), cancellationToken);
}
Console.WriteLine("");
Console.WriteLine("Total requests made : " + i);
Console.WriteLine("Requests which eventually succeeded : " + eventualSuccesses);
Console.WriteLine("Retries made to help achieve success : " + retries);
Console.WriteLine("Requests timed out by timeout policy : " + eventualFailuresDueToTimeout);
Console.WriteLine("Requests which failed after longer delay: " + eventualFailuresForOtherReasons);
}