Cache CI expire_in parsing

Previously the CI processor spent a surprising amount of time
validating the `expire_in` field for each build in the pipeline. It
turns out `ChronicDuration.parse` can be expensive because it uses
regular expressions and ActiveSupport numeric conversions.

We observe that builds often use a small set of `expire_in` values, so
we can cache the result of a previous validation.

For a pipeline like `gitlab-org/gitlab` that has 200 builds with 8
different `expire_in` values, we see a 28x improvement:

```
Calculating -------------------------------------
                 old     1.000  i/100ms
                 new    14.000  i/100ms
-------------------------------------------------
                 old      5.275  (± 0.0%) i/s -     27.000
                 new    149.409  (± 5.4%) i/s -    756.000

Comparison:
                 new:      149.4 i/s
                 old:        5.3 i/s - 28.32x slower
```

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/322386

Changelog: performance

lib/gitlab/ci/build/artifacts/expire_in_parser.rb

@@ -16,9 +16,7 @@ module Gitlab
           def validate_duration
             return true if never?
 
-            parse
-          rescue ChronicDuration::DurationParseError
-            false
+            cached_parse
           end
 
           def seconds_from_now
@@ -29,12 +27,28 @@ module Gitlab
 
           attr_reader :value
 
+          def cached_parse
+            return validation_cache[value] if validation_cache.key?(value)
+
+            validation_cache[value] = safe_parse
+          end
+
+          def safe_parse
+            parse
+          rescue ChronicDuration::DurationParseError
+            false
+          end
+
           def parse
             return if never?
 
             ChronicDuration.parse(value)
           end
 
+          def validation_cache
+            Gitlab::SafeRequestStore[:ci_expire_in_parser_cache] ||= {}
+          end
+
           def never?
             value.to_s.casecmp('never') == 0
           end

spec/lib/gitlab/ci/build/artifacts/expire_in_parser_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 RSpec.describe Gitlab::Ci::Build::Artifacts::ExpireInParser do
-  describe '.validate_duration' do
+  describe '.validate_duration', :request_store do
     subject { described_class.validate_duration(value) }
 
     context 'with never' do
@@ -20,14 +20,33 @@ RSpec.describe Gitlab::Ci::Build::Artifacts::ExpireInParser do
 
     context 'with a duration' do
       let(:value) { '1 Day' }
+      let(:other_value) { '30 seconds' }
 
       it { is_expected.to be_truthy }
+
+      it 'caches data' do
+        expect(ChronicDuration).to receive(:parse).with(value).once.and_call_original
+        expect(ChronicDuration).to receive(:parse).with(other_value).once.and_call_original
+
+        2.times do
+          expect(described_class.validate_duration(value)).to eq(86400)
+          expect(described_class.validate_duration(other_value)).to eq(30)
+        end
+      end
     end
 
     context 'without a duration' do
       let(:value) { 'something' }
 
       it { is_expected.to be_falsy }
+
+      it 'caches data' do
+        expect(ChronicDuration).to receive(:parse).with(value).once.and_call_original
+
+        2.times do
+          expect(described_class.validate_duration(value)).to be_falsey
+        end
+      end
     end
   end