Nested Block Until Done

[Olivia_99696]

I want to export 4 tables to 4 sheets in one Excel file. This worklfow works for me, but I am confused with the logic behind Block Until Done Tool.

My workflow has four nested Block Until Done Tools, marked in red 1 2 3 4.

Initially, I thought the Yellow Stream would run first, followed by the Orange Stream.

However, the Orange Stream contains a Union Tool that requires data from 3 parallel streams, so I expected it to be delayed.

And the Blue Stream will never start.

Surprisingly, all the streams work fine. How does this work?

[Peachyco]

I think you're expecting that Block Until Done (BUD) looks all the way down each stream. It doesn't work that way. BUDs only look at the immediately following tools.

The BUD-1 makes sure that the first Filter Tool gets the data before going to the second one, and so on. Once the data has been passed to the Filter Tools, BUD-1 no longer cares about the timing of the workflow.

The order of when you added the tools to the workflow also matters. Maybe Filter-1 looks like it would go first because of the layout, but you actually added Filter-2 to the workflow first and then rearranged later. This might mean that Filter-1 would wait for Filter-2 to run first, even though Filter-1 received its complete data first. To check the order of tool placement, you can look at their numbering.

To illustrate, consider this snapshot. This tells me that this Formula Tool is the 201st tool that I added to the workflow.

The overall timing of the workflow can be difficult to gauge. It can't really be judged just by the placement of BUDs and other tools.