Finally! Some real data to work with.

Just so we can compare like with like, here are your data & tests run on my machine:

So, even with your suspiciously unrealistic choice of dataset, using 1 worker thread requires 15% more cpu & with 4, 26% more. (And that's the original point, but I'll come back to that.)

But replacing every character of every line is ... let's just say extremely unrealistic for now. So let's see what happens when we use what is only a very slightly more realistic dataset with a 50% duty cycle:

C:\test>perl -le"print 'a 'x512 for 1..1e5" > 1kLines.txt

C:\test>perl -pe"s/a/A/g}{warn join' ',$., times" 1kLines.txt > output
+.cmp
100000 12.214 0.171 0 0 at -e line 1, <> line 100000.

C:\test>junk71 -T=1 1kLines.txt > output.cmp
Started Thu Mar 24 03:44:16 2011
Ended Thu Mar 24 03:44:31 2011
16.177 0.764 0 0 at C:\test\junk71.pl line 38, <> line 100000.

C:\test>junk71 -T=4 1kLines.txt > output.cmp
Started Thu Mar 24 03:44:44 2011
Ended Thu Mar 24 03:44:50 2011
19.468 4.492 0 0 at C:\test\junk71.pl line 38, <> line 100000.
[download]

Now the differences are rather more obvious. Ranging from 36% more with 1 worker, and 93% more for 4 workers.

And how about the length of those lines? I'd bet that of the data stored in text files around the world the vast majority of it has line lengths far shorter than 1K each. Even really huge datasets with really huge 'records' tend to wrap them at some terminal-friendly limit. Eg DNA & FASTA files.

So let's do something about that also. Cut the line length to a more reasonable 100 bytes and increase the number of lines to 1e6 to maintain approximate parity with the dataset size:

So, now with a dataset somewhat more likely to reflect the norm, we've got 1 worker taking 422% and 4 workers taking 1155% more. That's 4 to 11 times as long. Still a far cry from "my 120x" I hear you cry, but bear with me.

When I came to appraise the possibilities I looked for an existing file of roughly the right size and found a file I'd generated for some similar purpose. 5GB of random 'phrases' in typical 'text file sized' lines. Perfect!:

And so I saw the one-liner complete in (well) under 2 minutes. And from the very consistent lines/sec output, I projected (100e6 / 14387) = 6950 seconds or 115 minutes. If you (care to) remember that my original post contained no timing code, so the timing was done rather more crudely. Hence my factor of two exaggeration.

But, and here is the real point. Never in any of these tests, yours or mine, your dataset or mine, have any of us found a threads & queues solution that achieves a performance gain. And anything less than faster is a failure. Simply not worth the effort.

Not once. Not even your highly, (some might even say suspiciously), unrealistic dataset and duty cycle. Indeed, the more threads and queues you throw at the problem, the longer it damn well takes.

I'll let others decide for themselves about who followed a more realistic test scenario in the absence of any specifics about the OPs actual data and processing--which I asked for but never received.

Bottom line: A threads & queues solution will never solve the OPs problem. And I seriously doubt, but don't have the expertise to know, nor your code to try, that a forks & pipes solution will achieve much either. Assuming realistic datasets and duty cycles.

And the whole point of my posting some timing info was to force you to try and counter it. So the next time you get tempted to answer the OPs question with an untried, mind's eye solution:

Create the threads first and then have each thread load just the data it needs (and don't share it, of course). Then there won't be extra copies of that stuff created.

And only when pressed for more detail, did you 'fine tuning' that piece of off-the-cuff, based-on-nothing-but-what-you'd-read-somewhere, nonsense with more guesswork:

Having the parent read in the data and hand off each piece to the appropriate thread(s) (I'm guessing via Thread::Queue might be a good way) is the most general method that springs to my mind. I'd probably do something similar except using processes and simple pipes, as I've often done.

If you have neither the experience to know, nor the time to test your theories a little first, maybe you'll think twice, and so avoid wasting the OPs time pursuing impossible 'solutions'.

That's me done. Last word is yours.