Tuesday, 23 March 2010

Setting Physical Memory Limit for a .NET application

We needed to limit the physical memory used by a .NET application as it was taking too much of it and the other apps appeared to be in a struggle mode.

The straightforward way appeared to use Process.GetCurrentProcess().MaxWorkingSet. Strangely, no matter what we tried, this never worked. Yet to figure out why it does not work - if anyone has a clue, please ping.

Anyways, looking at options we came across job objects in Windows that allow setting the max working set. So the approach that finally worked was this:

1.) Create a Job object using CreateJobObject() Win32 call

2.) Setup the memory limits against this job using

3.) Assign our process to this job using AssignProcessToJob().

Now, when we look at the task manager, the physical memory assigned to this process never goes over the specified limit. All good.

Note that this is applicable only for the physical memory and not for the virtual memory - no limits can be set for this [?]. The physical memory limit is affected when the application is paged-in from the page file into the memory.

Thursday, 18 March 2010

Exploiting ObjectFromLresult() to get the IHTMLDocument2 from a window handle

Assume you have a window handle to a html control (which implements IHTMLDocument2) within a browser page (which is an IWebBrowser2), how would you access the HTML elements?

This is interesting as with just a window handle, it was relatively unknown on how that can be mapped to an object.

What you need to do is this:

1.) Register the windows message WM_HTML_GETOBJECT

2.) Send this message to the window handle we have in hand using a SendMessageTimeOut(). The out parameter in the lpdwResult returns you an UIntPtr to the object after the call.

3.) Next, use this out parameter as part of the ObjectFromLresult() call:
ObjectFromLresult(result from sendmessagetimeout, IHtmlDocument, 0)

4.) Cast the result from ObjectFromLresult() to IHTMLDocument2.

5.) Use the all property to get the HTML elements.

The powerfull function here definitely is the ObjectFromLResult() which effectively returns you an object that is 'accessible'. Accessible in terms of the user accessibility factor.

A framework worth checking out in this regard is the UIA framework that allows manipulating individual entities on the screen be it winforms, browser controls...