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Resolved Powerbuilder - User break out of a loop

  1. How-to
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  1. Jason Lipman
    Jason Lipman
  2. PowerBuilder
  3. Monday, 8 January 2024 18:50 PM UTC

PB 2017 R3

Hey everyone! I've never tried this before... Is there a way to trap a keypress while in a loop?

We are processing over 4 million rows in a loop. To handle memory, I am resetting and retrieving appropriate untouched rows after every ### rows. I can cancel the process with DBCancel and the RetrieveRow event during the retrieve. But I would like to allow the user to cancel while looping the ### number of rows if possible as well.

Any ideas?

Thanks!

Jason Lipman

  1. PowerBuilder (Appeon)
Embedded SQL input variable value max length
PBCLTRT115.msi
Responses (4)
John Fauss
John Fauss Accepted Answer Pending Moderation
  1. Monday, 8 January 2024 19:17 PM UTC
  2. PowerBuilder
  3. # 1

Hi, Jason - 

Some ideas to consider:

1. Async=1 DBParm option (not supported with the SQL Server SNC or MSO database client interface). More info here:
    https://docs.appeon.com/pb2022/connection_reference/Async.html

2. If the app is in a wait state while the database request is being executed and Async=1 is not an option, then using the Yield() PowerScript function won't help. You would need to execute the database operation in a separate thread in order to keep the main/GUI thread available and responsive.

Here are a couple of tech articles that may help:

    https://community.appeon.com/index.php/articles-blogs/tutorials-articles/2-powerbuilder/325-why-unresponsive-application-windows-are-ghosted-by-the-windows-o-s

    https://community.appeon.com/index.php/articles-blogs/tutorials-articles/2-powerbuilder/339-free-my-gui-multi-threading-in-powerbuilder

Best regards, John

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John Raghanti
John Raghanti Accepted Answer Pending Moderation
  1. Tuesday, 9 January 2024 13:10 PM UTC
  2. PowerBuilder
  3. # 2

We have done something similar. We had to put a Yield() into the loop. We added a boolean instance variable

 

ib_cancel = False

 

Then trapped the keypress and set the boolean to True. Inside the loop after the Yield(), check the value of ib_cancel and stop the processing if needed.

 

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Jason Lipman
Jason Lipman Accepted Answer Pending Moderation
  1. Tuesday, 9 January 2024 15:19 PM UTC
  2. PowerBuilder
  3. # 3

Thank you for the responses! Yield worked beautifully. In my case, there was no need for multi-threading. I think I did use Yield() many years ago, and did not recall this very simple solution. 

Jason

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John Fauss
  1. John Fauss
  2. Tuesday, 9 January 2024 16:04 PM UTC
That's great news, Jason! Thanks for letting us know what worked for you.
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Roland Smith
Roland Smith Accepted Answer Pending Moderation
  1. Tuesday, 9 January 2024 17:49 PM UTC
  2. PowerBuilder
  3. # 4

How many rows are processed between commits? Doing a commit after every row will slow it down. I would try every 100 rows to start. If too many updates are pending, the commit will take a long time and there might be blocking on the updated tables.

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Jason Lipman
  1. Jason Lipman
  2. Tuesday, 9 January 2024 19:41 PM UTC
Roland, I am actually looping a 4.6 million row table only extracting the Blob and saving it out to a directory for use by a different tool. To prevent any memory issues, I was thinking of re-retrieving the untouched data every 200 rows or so. I am not yet sure how many rows I can handle before there are memory concerns. I was also considering using GarbageCollect after every ??? rows to help prevent issues.

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Roland Smith
  1. Roland Smith
  2. Wednesday, 10 January 2024 16:04 PM UTC
I hope this is a onetime thing!

Can you do a retrieve with only the minimum columns needed to feed into a SELECTBLOB statement? The SELECTBLOB and code to write it to disk could go into the RetrieveRow event. A Yield function could be used to allow for updating progress on the window.
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