Demonstrates that ExcelAsyncUtil.Run can be used in a thread safe Excel function.
By default, Excel functions are executed on the main UI thread. You can use the IsThreadSafe attribute to mark a function that supports execution on a worker thread and use ExcelAsyncUtil.Run from it for asynchronous execution:
[ExcelFunction(IsThreadSafe = true)]
public static object SayHelloAsyncThreadSafe(string name)
{
return SayHelloAsync(nameof(SayHelloAsyncThreadSafe), name);
}
private static object SayHelloAsync(string callerFunctionName, string name)
{
int threadId = Thread.CurrentThread.ManagedThreadId;
return ExcelAsyncUtil.Run(callerFunctionName, new object[] { name }, () => SayHelloWithDelay(name, threadId));
}
private static string SayHelloWithDelay(string name, int threadId)
{
Thread.Sleep(2000);
return $"Hello {name} (thread {threadId})";
}Adding several calls to SayHelloAsyncThreadSafe and SayHelloAsyncNotThreadSafe to a worksheet and pressing Ctrl+Alt+F9 for recalculation demonstrates that thread safe functions are executed on worker threads and not thread safe functions are executed on the main UI thread:
=SayHelloAsyncThreadSafe("TS")
=SayHelloAsyncNotThreadSafe("!TS")
The sample project also includes SayHelloAsyncFast thread safe function that uses ExcelAsyncUtil.Run and returns immediately without any delay. And SayHelloAsyncSlow thread safe function that uses ExcelAsyncUtil.Run and returns a value after 10 seconds delay:
[ExcelFunction(IsThreadSafe = true)]
public static object SayHelloAsyncFast(string name)
{
return ExcelAsyncUtil.Run(nameof(SayHelloAsyncFast), new object[] { name }, () => $"Hello {name}");
}
[ExcelFunction(IsThreadSafe = true)]
public static object SayHelloAsyncSlow(string name)
{
return ExcelAsyncUtil.Run(nameof(SayHelloAsyncSlow), new object[] { name }, () => SayHelloWithDelay10(name));
}
private static string SayHelloWithDelay10(string name)
{
Thread.Sleep(10000);
return $"Hello {name}";
}You can test them like this:
=SayHelloAsyncFast("fast")
=SayHelloAsyncSlow("slow")