Chuma posted an interesting Long list is long challenge, last year October 2022. eyepopslikeamosquito created a separate thread one month later. Many solutions were provided by several folks.

My goal was keeping memory consumption low no matter if running a single thread or 20+ threads. Ideally, running more threads should run faster. It turns out that this is possible. Ditto, zero merge overhead as the keys are unique. Just move the elements from all the sub-maps over to a vector for sorting and output.

In a nut-shell, the following is the strategy used for the hash-map solutions in latest June 2023 refresh.

1. create many sub-maps and mutexes
2. parallel single-file via chunking versus parallel list of files
3. create a hash-value for the key and store the value with the key
4. determine the sub-map to use by hash-value MOD number-of-maps
5. there are total 963 sub-maps to minimize locking contention
6. randomness kicks in, allowing many threads to run

[download]

Thank you, Gregory Popovitch. He identified the last one-off error in my C++ chunking logic plus shared a couple suggestions. See issue 198. Thank you, eyepopslikeamosquito for introducing me to C++. Thank you, anonymous monk. There, our anon-friend mentioned the word parallel. So, we tried running parallel in C++. Eventually, chunking too. :)

In reply to Solving the Long List is Long challenge, finally? by marioroy

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