Re: [gentoo-dev] [PATCH] cargo.eclass: use CARGO_CRATE_URIS if already available

[Sam James <sam@gentoo.org>]

Michał Górny <mgorny@gentoo.org> writes:

> On Mon, 2023-07-31 at 12:41 +0200, Florian Schmaus wrote:
>> With 59dbfb80f748 ("cargo.eclass: Add variable alternative to
>> $(cargo_crate_uris)") the _cargo_set_crate_uris function was
>> introduced. This function runs when the elcass is inherited and sets
>> CARGO_CRATE_URIS.
>> 
>> Ebuilds that use $(cargo_crate_uris) in SRC_URI will again invoke this
>> function, even though CARGO_CRATE_URIS is already set. Avoiding this
>> unnecessary computation reduces the ebuild source time of
>> app-shells/nushell-0.83.0 from 21 ms to 14 ms.
>> 
>> This is a significant reduction when compared to the variable-setting
>> alternative that the commit 59dbfb80f748 ("cargo.eclass: Add variable
>> alternative to $(cargo_crate_uris)") introduced. Using the
>> variable-setting approach would reduce the ebuild source time only by a
>> little bit more than one millisecond.
>> 
>> Using
>> 
>> pk pkg source --bench 10s '=app-shells/nushell-0.83.0'
>> 
>> as benchmark, yields
>> 
>> >                           | Cached CARGO_CRATE_URIS | Non-Cached CARGO_CRATE_URIS |
>> > ---------------------------+-------------------------+-----------------------------|
>> > $(cargo_crate_uris)       | mean: 14.189ms          | mean: 21.445ms              |
>> > variable-setting approach | mean: 12.822ms          | mean: 12.852ms              |
>> 
>> full benchmark output
>> 
>> >                           | Cached CARGO_CRATE_URIS (this commit)                            | Non-Cached CARGO_CRATE_URIS                                      |
>> > ---------------------------+------------------------------------------------------------------+------------------------------------------------------------------|
>> > $(cargo_crate_uris)       | mean: 14.189ms, min: 13.646ms, max: 15.103ms, σ = 149µs, N = 705 | mean: 21.445ms, min: 20.79ms,  max: 22.832ms, σ = 228µs, N = 467 |
>> > variable-setting approach | mean: 12.822ms, min: 12.41ms,  max: 13.909ms, σ = 165µs, N = 780 | mean: 12.852ms, min: 12.367ms, max: 15.437ms, σ = 227µs, N = 779 |
>> 
>> Signed-off-by: Florian Schmaus <flow@gentoo.org>
>> ---
>>  eclass/cargo.eclass | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>> 
>> diff --git a/eclass/cargo.eclass b/eclass/cargo.eclass
>> index 70b6008d9cd8..5d6911801097 100644
>> --- a/eclass/cargo.eclass
>> +++ b/eclass/cargo.eclass
>> @@ -240,6 +240,14 @@ _cargo_set_crate_uris "${CRATES}"
>>  # Constructs a list of crates from its arguments.
>>  # If no arguments are provided, it uses the CRATES variable.
>>  cargo_crate_uris() {
>> +	# Use already existing value for CARGO_CRATE_URIS, computed by
>> +	# _cargo_set_crate_uris, when this function is invoked without
>> +	# arguments.
>> +	if [[ $# -eq 0 && -n "${CARGO_CRATE_URIS}" ]]; then
>> +		echo "${CARGO_CRATE_URIS}"
>> +		return
>> +	fi
>> +
>>  	local crates=${*-${CRATES}}
>>  	if [[ -z ${crates} ]]; then
>>  		eerror "CRATES variable is not defined and nothing passed as argument"
>
> This incorrectly assumes that the value of CRATES did not change which
> isn't guaranteed anywhere.

Ah, thanks! Now I remember - we discussed it before and rejected it for
this reason.