What volatile is actually good for

Today I was reading about something on SO and stumbled to this note about volatile keyword in C#, it seemed to be nice simple explanation of widely misunderstood term so I am sharing it here.

A good example is say you have 2 threads, one which always writes to a variable (say queueLength), and one which always reads from that same variable.

If queueLength is not volatile, thread A may write 5 times, but thread B may see those writes as being delayed (or even potentially in the wrong order).

A solution would be to lock, but you could also in this situation use volatile. This would ensure that thread B will always see the most up-to-date thing that thread A has written. Note however that this logic only works if you have writers who never read, and readers who never write, and if the thing you're writing is an atomic value. As soon as you do a single read-modify-write, you need to go to Interlocked operations or use a Lock.

I got this at below URL

http://stackoverflow.com/questions/154551/volatile-vs-interlocked-vs-lock#answer-154803

jQuery dynamic validation error messages

I am not a champ at asp.net mvc and found myself struggling with a task that at first I thought will be trivial, below is how I got through it :)

I wrote a custom validation attribute and needed to show validation messages as per values entered. Below is stripped down version of what I ended up doing:

Below lines add validation attribute named checkagainstmaxsumvalue that checks values of two fields and decides error messages dynamically

jQuery.validator.unobtrusive.adapters.add("checkagainstmaxsumvalue", ["dependentproperty1", "dependentproperty2"], function (options) {

    options.rules['checkagainstmaxsumvalue'] = {

        prop1: options.params['dependentproperty1'],

        prop2: options.params['dependentproperty2']

    };

});

jQuery.validator.addMethod("checkagainstmaxsumvalue", function (value, element, params) {

        var result = true;

        var prop1 = parseInt($('#' + params['prop1']).val(), 10);

        var prop2 = parseInt($('#' + params['prop2']).val(), 10);

        var errMsg = getErrorMessage(prop1, prop2);

        if (errMsg) {

            result = false;

        }

        return result;

    }, function (params, element) {

        var prop1 = parseInt($('#' + params['prop1']).val(), 10);

        var prop2 = parseInt($('#' + params['prop2']).val(), 10);

        return getErrorMessage(prop1, prop2);

    }

);

//Validation logic here, returns error message if validation fails 

//and empty string if success

function getErrorMessage(prop1, prop2) {

    var errMsg = "";

    if (prop1 < 20 && prop2 < 20) {

        errMsg = "Either of prop1 and prop2 should be greater than 20";

    } else if (prop1 + prop2 > 30) {

        errMsg = "Sum of prop1 and prop2 should be less than equal to 30";

    }

    return errMsg;

}

This all I did after reading below answer at every developer's life saver site SO :)
http://stackoverflow.com/questions/13352626/dynamic-jquery-validate-error-messages-with-addmethod-based-on-the-element#answer-13352987

This worked perfectly fine in my case but still there is concern that validation logic executes twice, once for deciding message and once for actual verification. This sounds a bit overkill but till now I didn't have a better option.