Function ThreadCountForLevel

src/OrcLib/ZipCreate.cpp:81–96

Cap the LZMA2 thread count so peak compression memory no longer scales with the host core count. The encoder splits 'mt' as (block-threads x match-finder-threads); bt4 (Normal and above) uses 2 match-finder threads, so total mt = 2 x block-threads, and block-threads is what multiplies memory. Allow up to 2 block-threads on 64-bit (mt=4) and a single solid block on 32-bit (mt=2) where the address s

// behaviour and keeps peak memory close to a single dictionary.
// Returns 0 to keep the library default (one thread per processor).
UInt32 ThreadCountForLevel(ZipCreate::CompressionLevel level)
{
    switch (level)
    {
        case ZipCreate::Normal:
        case ZipCreate::Maximum:
        case ZipCreate::Ultra:
        {
            const UInt32 cap = 2u;
            const UInt32 cores = ProcessorCount();
            return cores < cap ? cores : cap;
        }
        default:
            return 0;
    }
}

void StoreFileHashes(OrcArchive::ArchiveItems& items, bool releaseInputStreams)
{