new: install via nuget: Install-Package Core.Trying
A Fluent Way of Exception Handling
While doing some Filesystemwork I encountered alot of Access exceptions because a file is being opened to write multiple times. Even after closing the file explicitly a short timeframe exists in which the file could not be opened again. The simplest approach for me was to retry openening the file until it worked. To allow a more easy and more general way to handle exceptions I developed a small extensible try repeat framework which allows me to configure waiting and repeating strategies and also only react to specific exceptions. I have written a small fluent interface which allows easy usage:
varconfiguration=newTry().BeQuiet(true)// do not throw exceptions when action continouosly fails.Expect<AccessViolationException>()// only expect access violation exceptions.Repeat(5,1000)// repeat at most 5 times or until 1s of waiting time has passed.BackoffExponentially();// when actions fails backoff exponentially e.g. first wait 10 ms then 100 ms then 1000ms//configuration is reusablevarresult=configuration.Execute(()=>{/*something which potentially throws */});if(result){// successConsole.WriteLine("number of retries needed until success: "+result.FailedCount);}else{// failureConsole.WriteLine("time spent waiting [ms]: "+result.WaitedTime);Console.WriteLine("number of retries: "+result.FailedCount);Console.WriteLine("last throw exception message: "+result.LastException.Message);}// default configuration handles any exception// repeats 4 times at most and exponentially backs offTry.Default.Execute(()=>{/*some action which potentially throws*/});// returns the result of an operation when successfulvarresult=newTry().Execute(()=>3);Assert.AreEqual(3,result);varexceptionHandled=false;// expects RightException and calls a custom handler when it occurs// expect any other exception which will be ignored quitely// returns value of operation on successvarresult=newTry().Repeat(3).Expect<RightException>(ex =>{exceptionHandled=true;}).Expect<Exception>().Execute(context =>{switch(context.FailedCount){case0:thrownewWrongException();case1:thrownewRightException();case2:return"result";default:thrownewException();}});Assert.AreEqual("result",result);Assert.IsTrue(exceptionHandled);Be warned that this type of repeat on exception strategy should not be applied blindly …
I developed the library because I needed it but some terminology was researched. consulted sources:
http://msdn.microsoft.com/en-us/library/hh680905(v=pandp.50)http://stackoverflow.com/questions/1563191/c-sharp-cleanest-way-to-write-retry-logic