Allocation-free copy#613
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The output flux getters (`net_flux`, `lw_flux_up`, `sw_flux_dn`, ...) return single-level views of plain `(nlev, ncol)` presentation buffers, so a host wraps them with ClimaCore's `array2field` copy-free and in the correct memory order. A consumer that `copy(getter(solver))`s before wrapping materializes a full `(nlev, ncol)` field per getter per call; a diagnostics pass reading many fluxes every step turns that into large per-step allocations (observed as ~17 MB/step in a ClimaAtmos aquaplanet flame test, from ~12 such copies). RRTMGP itself is unchanged and its solve stays allocation-free; this documents the getter contract and adds a regression test so the copy-free guarantee can't silently regress. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
szy21
reviewed
Jul 14, 2026
| full = @allocated copy(g) # copy materializes a full field | ||
| read = @allocated (dst .= g) # reading needs no such copy | ||
| @test full >= length(g) * sizeof(eltype(g)) | ||
| @test read < full ÷ 4 |
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wow I didn't know this symbol ÷ exists
szy21
approved these changes
Jul 14, 2026
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Purpose
Documents copy-free flux getter, to make CPU branch allocation free
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