Introduce Processor

[pellared]

Introducing a Processor has no impact on the performance.

$ benchstat old.txt new.txt
goos: linux
goarch: amd64
pkg: go.opentelemetry.io/otel/sdk/log
cpu: Intel(R) Core(TM) i9-10885H CPU @ 2.40GHz
                    │   old.txt    │               new.txt               │
                    │    sec/op    │    sec/op     vs base               │
/no_attrs/Simple-16   451.4n ±  4%   453.2n ±  3%       ~ (p=0.684 n=10)
/no_attrs/Batch-16    470.7n ±  6%   436.2n ±  2%  -7.33% (p=0.000 n=10)
/3_attrs/Simple-16    653.2n ±  5%   661.8n ±  7%       ~ (p=0.280 n=10)
/3_attrs/Batch-16     687.9n ±  6%   660.4n ±  8%       ~ (p=0.436 n=10)
/5_attrs/Simple-16    767.1n ±  4%   779.6n ±  3%       ~ (p=0.165 n=10)
/5_attrs/Batch-16     833.2n ±  3%   772.5n ±  4%  -7.28% (p=0.000 n=10)
/10_attrs/Simple-16   2.076µ ±  3%   2.026µ ±  6%       ~ (p=0.210 n=10)
/10_attrs/Batch-16    2.489µ ±  7%   2.347µ ±  5%       ~ (p=0.063 n=10)
/40_attrs/Simple-16   6.010µ ±  4%   6.459µ ± 13%  +7.46% (p=0.005 n=10)
/40_attrs/Batch-16    8.201µ ± 10%   7.848µ ±  5%       ~ (p=0.165 n=10)
geomean               1.316µ         1.288µ        -2.12%

                    │    old.txt     │                new.txt                │
                    │      B/op      │     B/op      vs base                 │
/no_attrs/Simple-16     0.000 ± 0%       0.000 ± 0%       ~ (p=1.000 n=10) ¹
/no_attrs/Batch-16      0.000 ± 0%       0.000 ± 0%       ~ (p=1.000 n=10) ¹
/3_attrs/Simple-16      0.000 ± 0%       0.000 ± 0%       ~ (p=1.000 n=10) ¹
/3_attrs/Batch-16       1.000 ± 0%       1.000 ±  ?       ~ (p=0.303 n=10)
/5_attrs/Simple-16      0.000 ± 0%       0.000 ± 0%       ~ (p=1.000 n=10) ¹
/5_attrs/Batch-16       1.000 ± 0%       1.000 ± 0%       ~ (p=1.000 n=10) ¹
/10_attrs/Simple-16   1.392Ki ± 0%     1.392Ki ± 0%       ~ (p=1.000 n=10) ¹
/10_attrs/Batch-16    1.396Ki ± 0%     1.394Ki ± 0%  -0.14% (p=0.000 n=10)
/40_attrs/Simple-16   6.692Ki ± 0%     6.692Ki ± 0%       ~ (p=1.000 n=10) ¹
/40_attrs/Batch-16    6.705Ki ± 0%     6.699Ki ± 0%  -0.08% (p=0.000 n=10)
geomean                            ²                 -0.02%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

                    │   old.txt    │               new.txt               │
                    │  allocs/op   │ allocs/op   vs base                 │
/no_attrs/Simple-16   0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
/no_attrs/Batch-16    0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
/3_attrs/Simple-16    0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
/3_attrs/Batch-16     0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
/5_attrs/Simple-16    0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
/5_attrs/Batch-16     0.000 ± 0%     0.000 ± 0%       ~ (p=1.000 n=10) ¹
/10_attrs/Simple-16   9.000 ± 0%     9.000 ± 0%       ~ (p=1.000 n=10) ¹
/10_attrs/Batch-16    9.000 ± 0%     9.000 ± 0%       ~ (p=1.000 n=10) ¹
/40_attrs/Simple-16   13.00 ± 0%     13.00 ± 0%       ~ (p=1.000 n=10) ¹
/40_attrs/Batch-16    13.00 ± 0%     13.00 ± 0%       ~ (p=1.000 n=10) ¹
geomean                          ²               +0.00%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

Yet it makes implementing decorators that e.g. alters a log record simpler.

Without Processor:

var pool = sync.Pool{
	New: func() any {
		b := make([]Record, 0, 1)
		return &b
	},
}

type timestampDecorator struct {
	Exporter
}

func (e timestampDecorator) Export(ctx context.Context, records []Record) error {
	bPtr := pool.Get().(*[]Record)
	defer func() {
		*bPtr = (*bPtr)[:0]
		pool.Put(bPtr)
	}()
	b := *bPtr

	for _, r := range records {
		r = r.Clone()
		r.SetObservedTimestamp(time.Date(1988, time.November, 17, 0, 0, 0, 0, time.UTC))
		b = append(b, r)
	}

	return e.Exporter.Export(ctx, b)
}

With Processor:

type timestampDecorator struct {
	Exporter
}

func (e timestampDecorator) Export(ctx context.Context, records []Record) error {
	bPtr := pool.Get().(*[]Record)
	defer func() {
		*bPtr = (*bPtr)[:0]
		pool.Put(bPtr)
	}()
	b := *bPtr

	for _, r := range records {
		r = r.Clone()
		r.SetObservedTimestamp(testTimestamp)
		b = append(b, r)
	}

	return e.Exporter.Export(ctx, b)
}