That sounds like a good case for memory mapped files
A memory-mapped file contains the contents of a file in virtual memory. This mapping between a file and memory space enables an application, including multiple processes, to modify the file by reading and writing directly to the memory. Starting with the .NET Framework 4, you can use managed code to access memory-mapped files in the same way that native Windows functions access memory-mapped files
http://msdn.microsoft.com/en-us/library/dd997372(v=vs.110).aspx
http://msdn.microsoft.com/en-us/library/vstudio/system.io.memorymappedfiles.memorymappedfile
A thread processes the data
Is that an ASP.Net thread? I would not perform that type of task within the context of IIS (why not). Instead, I would propose the shared memory be managed by a separate process, outside of IIS, such as a Windows Service.
The memory mapped file mechanism is well-suited to a Windows Service updating the data, and individual ASP.Net worker threads accessing the data as needed.