Updating client UI while waiting for DataSnap

Question

I created a MDI Delphi app in Delphi XE2 that connects to a DataSnap server via a TSQLConnection component (driver = datasnap). A right-click on the TSQLConnection at design-time lets me generate the DataSnap client classes (ProxyMethods).

My goal is to have an elapsed time clock [0:00] on the client side that shows how long a DataSnap request takes to service, updated every 1 second. The two approaches that I have tried, but don't work are:

Method #1

Use a TTimer with a 1 second interval that updates the elapsed time clock while a ProxyMethod is being execute. I enable the timer just before calling the ProxyMethod. While the ProxyMethod is running, the OnTimer event doesn't fire -- a breakpoint in the code is never hit.

Method #2

Same as Method #1, except the timer is a TJvThreadTimer. While the ProxyMethod is running, the OnTimer event fires, but the OnTimer code doesn't get execute until after the ProxyMethod completes. This is evident because a breakpoint in the OnEvent code gets hit in rapid succession after the ProxyMethod completes -- like the OnTimer events have all been queued in the main VCL thread.

Furthermore, clicking anywhere on the client app while a slow ProxyMethod is running makes the app appear to be hung ("Not Responding" appears in title-bar).

I think the best solution is to move the execution of the ProxyMethods to a separate thread. However, there must be an existing solution -- because the related hung app issue seems like it would be a common complaint. I just can't find the solution.

Any suggestions are appreciated. Otherwise, I will resign myself to moving the ProxyMethod execution into a separate thread.

Answer 1

You have identified the fundamental problem. Your query is running in the UI thread and blocks that thread whilst it runs. No UI updates can occur, timer messages cannot fire etc.

I think the best solution is to move the execution of the ProxyMethods to a separate thread. However, there must be an existing solution -- because the related hung app issue seems like it would be a common complaint. I just can't find the solution.

You have already found the only solution to the problem. You must run your long-running query in a thread other than the UI thread.