Suppose that you have a single-processor computer that has been configured to use, say, N threads.

They open up the possibility of using remote servers much more efficiently than can be done using a single thread. They allow Excel to make the most of a multi-processor or multi-core computer. The call to xlAutoFree or xlAutoFree12 is made before the next function call on that thread.įor XLL developers, there are benefits for creating thread-safe functions: Where an XLL function returns an XLOPER or XLOPER12 with xlbitDLLFree set, Excel uses the same thread on which the function call was made to call xlAutoFree or xlAutoFree12. Excel uses one thread (its main thread) to call all commands, thread-unsafe functions, xlAuto functions (except xlAutoFree and xlAutoFree12), and COM and Visual Basic for Applications (VBA) functions. You can also write and register XLL functions as being thread safe.

Most of the built-in worksheet functions starting in Excel 2007 are thread safe. Therefore, thread-safe cells, or cells that only contain functions that are thread safe, can be allotted to concurrent threads, subject to the usual recalculation logic of needing to be calculated after their precedents. On a multi-processor or multi-core computer, the default number of threads is equal to the number of processors or cores. However, starting in Excel 2007, Excel can be configured to use from 1 to 1024 concurrent threads for worksheet calculation. Versions of Microsoft Excel earlier than Excel 2007 use a single thread for all worksheet calculations. Applies to: Excel 2013 | Office 2013 | Visual Studio

Microsoft excel 2011 multithread