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Asked: 2026-05-12T05:08:38+00:00

I am working on maintaining someone else’s code that is using multithreading, via two

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I am working on maintaining someone else’s code that is using multithreading, via two methods:

1: ThreadPool.QueueUserWorkItem(New WaitCallback(AddressOf ReadData), objUpdateItem)

2: Dim aThread As New Thread(AddressOf LoadCache)
   aThread.Start()

However, on a dual core machine, I am only getting 50% CPU utlilization, and on a dual core with hyperthreadin enabled machine, I am only getting 25% CPU utilization.

Obviously threading is extremely complicated, but this behaviour would seem to indicate that I am not understanding some simple fundamental fact?

UPDATE

The code is too horribly complex to post here unfortunately, but for reference purposes, here is roughly what happens….I have approx 500 Accounts whose data is loaded from the database into an in memory cache…each account is loaded individually, and that process first calls a long running stored procedure, followed by manipulation and caching of the returned data. So, the point of threading in this situation is that there is indeed a bottleneck hitting the database (ie: the thread will be idled for up to 30 seconds waiting for the query to return), so we thread to allow others to begin processing the data they have received from Oracle.

So, the main thread executes: 

ThreadPool.QueueUserWorkItem(New WaitCallback(AddressOf ReadData), objUpdateItem)

Then, the ReadData() then proceeds to execute (exactly once): 

Dim aThread As New Thread(AddressOf LoadCache)
aThread.Start()

And this is occurring in a recursive function, so the QueueUserWorkItem can be executing multiple times, which in turn then executes exactly one new thread via the aThread.Start

Hopefully that gives a decent idea of how things are happening.

So, under this scenario, should this not theoretically pin both cores, rather than maxing out at 100% on one core, while the other core is essentially idle?

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1 Answer

  1. Editorial Team

    That code starts one thread that will go an do something. To get more than one core working you need to start more than one thread and get them both busy. Starting a thread to do some work, and then having your main thread wait for it won’t get the task done any quicker. It is common to start a long running task on a background thread so that the UI remains responsive, which may be what this code was intended to do, but it won’t make the task get done any quicker.

    @Judah Himango – I had assumed that those two lines of code were samples of how multi-threading were being achieved in two different places in the program. Maybe the OP can clarify if this is the case or if these two lines really are in the one method. If they are part of one method then we will need to see what the two methods are actually doing.

    Update:
    That does sound like it should max out both cores. What do you mean by recursivly calling ReadData()? If each new thread is only calling ReadData at or near its end to start the next thread then that could explain the behaviour you are seeing.
    I am not sure that this is actaully a good idea. If the stored proc takes 30 seconds to get the data then presumably it is placing a fair load on the database server. Running it 500 times in parallel is just going to make things worse. Obviously I don’t know your database or data, but I would look at improving the performance of the stored proc.
    If multi threading does look like the way forward, then I would have a loop on the main thread that calls ThreadPool.QueueUserWorkItem once for each account that needs loading. I would also remove the explicit thread creation and only use the thread pool. That way you are less likely to starve the local machine by creating too many threads.

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