WhileActivity and ActivityExecutionContext in WF

WhileActivity is a special activity in WF when ActivityExecutionContext (AEC) is concerned, because it creates a new AEC for each iteration.

Why? You can know the reason from common programming languages. For example, the below C# while statement adds/removes local variables from stack for each iteration:
while (conditionIsMet)
string output = DateTime.Now.ToString();
int count = 0;

WF WhileActivity has similar logic for each iteration: to create a new AEC based on the template activity (e.g. the SequenceActivity inside the WhileActivity).

Will the new AEC be destroyed at the end of each iteration? You may think "Of course! This is an obvious question". But the answer is "yes or no".

The answer is yes for normal cases without the need for compensation. There will be only one new AEC in memory for the iterations.

But the answer is no when compensation is needed. If a CompensatableActivity is defined inside the WhileActivity and when an exception occurrs in one iteration, all the previous iterations will be compensated. That means all previous AEC's can not be destroyed after each iteration. They have to be in memory for compensation purpose.

According to Krishnan:"The runtime will clean up execution contexts after each WhileActivity iteration. But only if you don't have an ICompensatableActivity inside (if you do, the EC's will stay in memory until the next persistence point.)"

XmlSerializer may cause memory leak

In my previous post, I mentioned XmlSerializer.dll is needed to serialize/deserialize types during web service call. But I did not know a potential memory leak problem until today from an excellent MSDN article: Do not use the overload of XmlSerializer constructor that takes the XML root element name as its second parameter!

As you may know, once a .NET assembly is loaded into memory, it will not be unloaded until the hosting AppDomain is unloaded. XmlSerializer constructor generates a temporary assembly for the type to be serialized using reflection. Because the code generation is expensive, the assembly is cached in memory on a per-type basis.

For example, the following code will create a cached assembly for type Employee:
XmlSerializer serializer = new XmlSerializer(typeof(Employee));

Whenever an Employee object is to be serialized, the cached assembly will be used.

But sometimes, we may want to change XML root name in the serialized XML message in a web service. An option is to call an overloaded constructor with XML root name as a parameter:
XmlSerializer serializer = new XmlSerializer(typeof(Employee), 
new XmlRootAttribute("Manager"));

Because the root name parameter is supposed to be dynamic, XmlSerializer will not cache the generated temporary assembly. It will generate a new assembly every time you create a new XmlSerializer with that parameter, and the generated assembly will stay in memory unless AppDomain is unloaded. So more and more generated assembly will stay in memory -- memory is being leaked!

If the root name is static, you can use XmlRootAttribute on the class to change root name of the serialized type; if the root name is dramatically dynamic, there is no easy way to solve the leak problem yet ...

That so-called security feature is still in IE 7 ?!

I believe you saw this warning window for many times when using IE. The reason is the web page of HTTPS URL includes both secure (HTTPS) and nonsecure (HTTP) content. When you view page source, you can see there is image, CSS source, JavaScript src, or other content that begins with "http://", not "https://".

I do not know the reason why IE team still keep this "feature" in IE 7:

1) Why should developer put HTTPS for a common image in web page? A common image should be fetched using HTTP directly because it is also shared by other nonsecure site
2) If I embed google map in a secure site, why should I use HTTPS for google content?

Although developers can write code to map URL from HTTPS to HTTP on web server to solve the problem, although users can change IE security options to enable "Display mixed content", one thing is for sure: This feature of IE is useless and annoying.