[Interest] [External]Re: How to get QtConcurrent to do what I want?

Konstantin Shegunov kshegunov at gmail.com
Tue Feb 1 14:28:42 CET 2022

On Mon, Jan 31, 2022 at 7:15 PM Murphy, Sean <Sean.Murphy at centauricorp.com>

>   1. Creating 60,000 QObjects in a single thread appears to be slow


Ehm, maybe I'm not understanding something, but why do you need objects to
begin with?

> The actual loop is this:
>     // generate each tile with its assignment
> [snip]

What's the significance of the tiles? As far as I can tell from your
requirements, you don't care about
the "true geometry" of the data.

At least to me it seems you want something like (pseudo algorithm):

1) Start QThread::idealThreadCount threads (QThread::create<> / std::thread)
2) Each thread works on "total samples" / QThread::idealThreadCount buffers
that are completely independent.
2.1) Each thread goes through each sample from a partially mapped (from the
file) buffer, takes the min/max to get the dynamic range
2.2) Sync the threads to get the global min/max
2.3) Go through each of the buffers a second time to normalize the dynamic
range (again no tiles involved, just samples)
3) Done.

Note: As each thread works on its own piece of data in both cases there's
no sync required at any one point - you just read/write different parts of
the same thing. Which is true both for when you load/write from/to a file
and from/to memory.

What am I missing here?

Kind regards,
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