Writing code to run the last method to throw exceptions in a multithreaded web application
I wrote several try-catch blocks for various methods today, and I thought it would be nice to have a utility method that automatically calls the method again for the multiple times given in the parameter at a specific time.
However, I thought to myself: the method / property etc. that would throw the exception would be at the top of the stacktrace (are property calls being received on the stack?) In a single threaded application (so an application without thread related code). So I can just get the method name at the top and call it dynamically again.
So, I would have code like:
string s = StackTrace.GetFrame (0) .GetMethodName; (I can't remember the exact syntax).
With this method, I can accomplish it with an activator or one of several ways.
But in a multi-threaded application, I could run multiple methods at once and I don't know which one ends up first / last. Therefore, I cannot expect the method I am writing the try-catch block for to be at the top of the stack.
How can I achieve this?
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While I doubt the need for an automatic retry mechanism (random retry will really help you in so many situations where you need a utility method?) - using StackTrace and Reflection is, at best, a terribly complex solution.
Not that I am suggesting that anyone actually use this code, but I would probably go with a delegate based approach to this particular problem:
public static class Extensions {
public static void Try(this Action a, int maxTries) {
new (Func<bool>(() => { a(); return true; })).Try(maxTries);
}
public static TResult Try<TResult>(this Func<TResult> f, int maxTries) {
Exception lastException = null;
for (int i = 0; i < maxTries; i++) {
try {
return f();
} catch (Exception ex) {
lastException = ex;
}
}
throw lastException;
}
}
The usage is a bit unorthodox but pretty clear:
// Set a property
new Action(() => myObject.Property = 5).Try(5);
// With a return value
var count = new Func<int>(() => myList.Count).Try(3);
You can't embed lambda in a method, but you can have a somewhat fluent interface:
Utilities.Try(
() => MyObject.Property = 5
).Repeat(5);
And multi-line methods:
Utilities.Try(() => {
MyObject.Property1 = 5;
MyObject.Property2 = 6;
MyObject.Property3 = 7;
}).Repeat(5);
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Mark code is probably better, but here is mine ...
If you really want to do something like this, I would use code something like this. Yes, you still have to manually call it, but your idea of indiscriminately repeating EVERYTHING except methods is really a very bad idea.
public class TryAgain
{
public delegate void CodeToTryAgain ();
public static void Repeat<E>(int count, CodeToTryAgain code) where E : Exception
{
while (count-- > 0)
{
try
{
code();
return;
}
catch (E ex)
{
Console.WriteLine("Caught an {0} : {1}", typeof(E).Name, ex.Message);
// ignoring it!
}
}
}
}
And then you call your opt-out method, ThrowTwice
or whatever you want to do, for example:
TryAgain.Repeat<MyException>(5, delegate()
{
ThrowTwice();
});
In this example, the Repeat method will ignore all MyExceptions by trying to call ThrowTwice up to 5 times ...
You can add your own sleeping and timeouts and whatever.
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