Here you will find a script to cancel all list workflows (not site workflows) running in a given site collection in the most efficient manner possible (that I can think of) while still only using the SharePoint API. A better approach still would be to query the SharePoint workflows SQL table to identify the running workflows so as to avoid iterating all site collection webs and lists. Unfortunately there is no ‘GetAllRunningWorkflows(SPSite)’ method available via the API. I imagine that this approach should be satisfactory in the majority of cases though.
There are a number of posts on the web with code somewhat similar to this, at least with code that aims to achieve the same outcome. Of all the posts which I found they all performed this function in a very inefficiency manner, iterating the SPListItemCollection for every list in the site collection. This may be fine in many circumstances but I wanted something that would run faster with less strain on the server.
I have achieved this by checking for workflow associations on a list before iterating the items as well querying the list items and where a workflow column exists checking to see if the list item needs to be returned at all. When returning the list items, I am querying with ViewFieldsOnly so that less data is returned.
This script also accepts an optional parameter that specifies which workflow associations should be canceled if you are not looking to cancel all of the workflow associations but just those of a specific name.
NB: The script contains a reference to a help function
GetNestedCaml which I have defined in a separate post which can be found here.
As the script sample is quite large I suggest clicking the ‘view raw’ link at the bottom of the sample to view it.