Re: Help - Timing Logic

Thanks for the reply.

I do need all 4 threads running (maybe even more in the future). I can not delete the row from the table... it needs to be there for later update use. I am considering marking each row at insert (1 - 4) then having each of the 4 threads only select a row based on the mark. It's becoming a little tricky... it would be great if I could lock a single row when selecting it.


"jeff" <jhersey at allnorth dottt com> wrote in message news:OPCyvDwEHHA.4740@xxxxxxxxxxxxxxxxxxxxxxx

Question:

What is the reason for the 4 threads?

Do you need all these threads processing the same dataset?

Just asking, maybe you could change your approach to avoid this problem...

If not, investigate Record Locking / Transactions...

How are you retrieving your records in to memory for processing ...

ie,
- are you selecting on the entire contents of a 'message' table and looping through an in-memory dataset...

- do you retrieve 'chunks' or rows from the message table based on parameters...

You could use the internal locking mechanisms of the database to achieve this ... but procede with caution...

Start Transaction...
SELECT * FROM MESSAGE TABLE
...
stuff this into a data table on the desktop
...
DELETE * FROM MESSAGE TABLE
...
punt / clean the table.
...
End Transaction.

The transactions places locks on the table ... but selecting the entire tables contents ... you are essentially 'LOCKING' the entire table until the transaction is over...

So, each thread's 'retrieve' process will have to wait in line until the select and delete are processed. As well, anything triggering 'New Messages to be Added' will be delayed until the Transaction is completed...

You may impact the overall performance of you application ... need to investigate.

If locking does not work for you, you will need to implement some type of logging / checking approach...

ie... have a log table...once a process has sent the message, write to a log table ... message sent. Before each message is compiled and sent, check the log table to see if another process has sent the message...if not, send you message...


A snip of code would be great to figure out how you are retrieving a list of messages and how you are processing each record...

Jeff.


"Jay" <someone@xxxxxxxxxxxxx> wrote in message news:O2phzwvEHHA.4280@xxxxxxxxxxxxxxxxxxxxxxx
I have a multi threaded VB.NET application (4 threads) that I use to send text messages to many, many employees via system.timer at a 5 second interval. Basically, I look in a SQL table (queue) to determine who needs to receive the text message then send the message to the address. Only problem is, the employee may receive up to 4 of the same messages because each thread gets the recors then sends the message. I need somehow to prevent this... just can't think of how. Somehow I need the other threads to know that another thread is already using that record and move on to the next record. I thought of getting the record then marking it (column value) as in use and writing the code to look for records only where not in use... problem is all 4 run fast enough to all use/mark the row. Any thoughts?

Thanks a lot.

Jay




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