On 12/05/2024 04.26, Michał Górny wrote:
> Unpack crates in parallel using xargs to utilize multicore systems
> better.  Perform checksumming via a single sha256sum invocation.
> 
> For dev-python/watchfiles, this speeds up unpacking on my machine
> from 2.6 s to 0.75 s (warm cache).
> 
> Signed-off-by: Michał Górny <mgorny@gentoo.org>
> ---
>   eclass/cargo.eclass | 56 ++++++++++++++++++++++++++-------------------
>   1 file changed, 33 insertions(+), 23 deletions(-)
> 
> diff --git a/eclass/cargo.eclass b/eclass/cargo.eclass
> index 0f2da982f60c..5a16d3a30528 100644
> --- a/eclass/cargo.eclass
> +++ b/eclass/cargo.eclass
> @@ -329,40 +329,50 @@ _cargo_gen_git_config() {
>   cargo_src_unpack() {
>   	debug-print-function ${FUNCNAME} "$@"
>   
> -	mkdir -p "${ECARGO_VENDOR}" || die
> -	mkdir -p "${S}" || die
> +	mkdir -p "${ECARGO_VENDOR}" "${S}" || die
>   
>   	local archive shasum pkg
> +	local crates=()
>   	for archive in ${A}; do
>   		case "${archive}" in
>   			*.crate)
> -				# when called by pkgdiff-mg, do not unpack crates
> -				[[ ${PKGBUMPING} == ${PVR} ]] && continue
> -
> -				ebegin "Loading ${archive} into Cargo registry"
> -				tar -xf "${DISTDIR}"/${archive} -C "${ECARGO_VENDOR}/" || die
> -				# generate sha256sum of the crate itself as cargo needs this
> -				shasum=$(sha256sum "${DISTDIR}"/${archive} | cut -d ' ' -f 1)
> -				pkg=$(basename ${archive} .crate)
> -				cat <<- EOF > ${ECARGO_VENDOR}/${pkg}/.cargo-checksum.json
> -				{
> -					"package": "${shasum}",
> -					"files": {}
> -				}
> -				EOF
> -				# if this is our target package we need it in ${WORKDIR} too
> -				# to make ${S} (and handle any revisions too)
> -				if [[ ${P} == ${pkg}* ]]; then
> -					tar -xf "${DISTDIR}"/${archive} -C "${WORKDIR}" || die
> -				fi
> -				eend $?
> +				crates+=( "${archive}" )
>   				;;
>   			*)
> -				unpack ${archive}
> +				unpack "${archive}"
>   				;;
>   		esac
>   	done
>   
> +	if [[ ${PKGBUMPING} != ${PVR} ]]; then
> +		pushd "${DISTDIR}" >/dev/null || die
> +
> +		ebegin "Unpacking crates"
> +		printf '%s\0' "${crates[@]}" |
> +			xargs -0 -P "$(makeopts_jobs)" -n 1 -- \

Consider using get_makeopts_jobs instead of makeopts_jobs, as it 
searches more variables for --jobs.

N.B.: If this where asking for a load-average limit, then using 
get_makeopts_loadavg would be the ideal way to pick up portage's default 
wrt --load-average. Therefore we should IMHO encourage using the 
get_makeopts_* functions over the (legacy?) non-get_ variants.

> +				tar -x -C "${ECARGO_VENDOR}" -f
> +		assert
> +		eend $?
> +
> +		while read -d '' -r shasum archive; do
> +			pkg=${archive%.crate}
> +			cat <<- EOF > ${ECARGO_VENDOR}/${pkg}/.cargo-checksum.json || die
> +			{
> +				"package": "${shasum}",
> +				"files": {}
> +			}
> +			EOF
> +
> +			# if this is our target package we need it in ${WORKDIR} too
> +			# to make ${S} (and handle any revisions too)
> +			if [[ ${P} == ${pkg}* ]]; then
> +				tar -xf "${archive}" -C "${WORKDIR}" || die
> +			fi
> +		done < <(sha256sum -z "${crates[@]}" || die)
> +
> +		popd >/dev/null || die
> +	fi
> +
>   	cargo_gen_config
>   }
>