Move log.Processor.Enabled to independent FilterProcessor interfa…

…ced type (open-telemetry#5692)

Closes open-telemetry#5425 

Our current log `Processor` interface contains more functionality than
the [OTel
spec](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/sdk.md#logrecordprocessor-operations).
The additional functionality allows processors to report back to the API
if a Record should be constructed and emitted or not, which is quite
helpful[^1][^2][^3][^4][^5].

This removes the `Enabled` method from the `Processor` type. It adds
this functionality a new optional and experimental `FilterProcessor`
interface type. The logger and provider are updated to check for this
optional interface to be implemented with the configured processors and
uses them to back the `Logger.Enabled` method, preserving existing
functionality.

By making this change:

- The `Processor` interface is now compliant with the OTel spec and does
not contain any additional unspecified behavior.
- All `Processor` implementations are no longer required to implement an
`Enabled` method. The default, when they do not implement this method,
is to assume they are enabled.

### Benchmark

```terminal
goos: linux
goarch: amd64
pkg: go.opentelemetry.io/otel/sdk/log
cpu: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
                │   old.txt    │              new7.txt               │
                │    sec/op    │   sec/op     vs base                │
LoggerEnabled-8   133.30n ± 3%   32.36n ± 3%  -75.72% (p=0.000 n=10)

                │  old.txt   │            new7.txt            │
                │    B/op    │    B/op     vs base            │
LoggerEnabled-8   0.000 ± 0%   0.000 ± 0%  ~ (p=1.000 n=10) ¹
¹ all samples are equal

                │  old.txt   │            new7.txt            │
                │ allocs/op  │ allocs/op   vs base            │
LoggerEnabled-8   0.000 ± 0%   0.000 ± 0%  ~ (p=1.000 n=10) ¹
¹ all samples are equal
```

This is a significant performance improvement due to the `Record` no
longer being converted from the API version to the SDK version.

[^1]: https://pkg.go.dev/go.opentelemetry.io/contrib/processors/minsev
[^2]:
https://pkg.go.dev/go.opentelemetry.io/otel/sdk/log#BatchProcessor.Enabled
[^3]:
https://pkg.go.dev/go.opentelemetry.io/otel/sdk/log#SimpleProcessor.Enabled
[^4]:
https://github.com/open-telemetry/opentelemetry-go-contrib/blob/af75717ac4fb3ba13eaea83b88301723122060cf/bridges/otelslog/handler.go#L206-L211
[^5]:
https://github.com/open-telemetry/opentelemetry-go-contrib/blob/d0309ddd8c5714af1cd9dbe8b39b7e8f10485679/bridges/otelzap/core.go#L142-L146

---------

Co-authored-by: Robert Pająk <[email protected]>
Co-authored-by: Sam Xie <[email protected]>

CHANGELOG.md

@@ -22,6 +22,10 @@ The next release will require at least [Go 1.22].
 - Zero value of `SimpleProcessor` in `go.opentelemetry.io/otel/sdk/log` no longer panics. (#5665)
 - Add `Walk` function to `TraceState` in `go.opentelemetry.io/otel/trace` to iterate all the key-value pairs. (#5651)
 - Bridge the trace state in `go.opentelemetry.io/otel/bridge/opencensus`. (#5651)
+- The `FilterProcessor` interface type is added in `go.opentelemetry.io/otel/sdk/log/internal/x`.
+  This is an optional and experimental interface that log `Processor`s can implement to instruct the `Logger` if a `Record` will be processed or not.
+  It replaces the existing `Enabled` method that is removed from the `Processor` interface itself.
+  It does not fall within the scope of the OpenTelemetry Go versioning and stability [policy](./VERSIONING.md) and it may be changed in backwards incompatible ways or removed in feature releases. (#5692)
 - Support [Go 1.23]. (#5720)
 
 ### Changed
@@ -30,6 +34,8 @@ The next release will require at least [Go 1.22].
 - `SimpleProcessor.Enabled` in `go.opentelemetry.io/otel/sdk/log` now returns `false` if the exporter is `nil`. (#5665)
 - Update the concurrency requirements of `Exporter` in `go.opentelemetry.io/otel/sdk/log`. (#5666)
 - `SimpleProcessor` in `go.opentelemetry.io/otel/sdk/log` synchronizes `OnEmit` calls. (#5666)
+- The `Processor` interface in `go.opentelemetry.io/otel/sdk/log` no longer includes the `Enabled` method.
+  See the `FilterProcessor` interface type added in `go.opentelemetry.io/otel/sdk/log/internal/x` to continue providing this functionality. (#5692)
 - The `SimpleProcessor` type in `go.opentelemetry.io/otel/sdk/log` is no longer comparable. (#5693)
 - The `BatchProcessor` type in `go.opentelemetry.io/otel/sdk/log` is no longer comparable. (#5693)
 - `NewMemberRaw`, `NewKeyProperty` and `NewKeyValuePropertyRaw` in `go.opentelemetry.io/otel/baggage` allow UTF-8 string in key. (#5132)
@@ -50,6 +56,11 @@ The next release will require at least [Go 1.22].
 - Correct comments for the priority of the `WithEndpoint` and `WithEndpointURL` options and their corresponding environment variables in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc` and `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#5641)
 - Correct comments for the priority of the `WithEndpoint` and `WithEndpointURL` options and their corresponding environment variables in `go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp`. (#5650)
 
+### Removed
+
+- The `Enabled` method of the `SimpleProcessor` in `go.opentelemetry.io/otel/sdk/log` is removed. (#5692)
+- The `Enabled` method of the `BatchProcessor` in `go.opentelemetry.io/otel/sdk/log` is removed. (#5692)
+
 <!-- Released section -->
 <!-- Don't change this section unless doing release -->
 

sdk/log/batch.go

@@ -196,11 +196,6 @@ func (b *BatchProcessor) OnEmit(_ context.Context, r *Record) error {
 	return nil
 }
 
-// Enabled returns if b is enabled.
-func (b *BatchProcessor) Enabled(context.Context, Record) bool {
-	return !b.stopped.Load() && b.q != nil
-}
-
 // Shutdown flushes queued log records and shuts down the decorated exporter.
 func (b *BatchProcessor) Shutdown(ctx context.Context) error {
 	if b.stopped.Swap(true) || b.q == nil {

sdk/log/batch_test.go

@@ -47,7 +47,6 @@ func TestEmptyBatchConfig(t *testing.T) {
 		ctx := context.Background()
 		record := new(Record)
 		assert.NoError(t, bp.OnEmit(ctx, record), "OnEmit")
-		assert.False(t, bp.Enabled(ctx, *record), "Enabled")
 		assert.NoError(t, bp.ForceFlush(ctx), "ForceFlush")
 		assert.NoError(t, bp.Shutdown(ctx), "Shutdown")
 	})
@@ -270,14 +269,6 @@ func TestBatchProcessor(t *testing.T) {
 		assert.Equal(t, 3, e.ExportN())
 	})
 
-	t.Run("Enabled", func(t *testing.T) {
-		b := NewBatchProcessor(defaultNoopExporter)
-		assert.True(t, b.Enabled(ctx, Record{}))
-
-		_ = b.Shutdown(ctx)
-		assert.False(t, b.Enabled(ctx, Record{}))
-	})
-
 	t.Run("Shutdown", func(t *testing.T) {
 		t.Run("Error", func(t *testing.T) {
 			e := newTestExporter(assert.AnError)

sdk/log/doc.go

@@ -32,5 +32,8 @@ at a single endpoint their origin is decipherable.
 
 See [go.opentelemetry.io/otel/log] for more information about
 the OpenTelemetry Logs Bridge API.
+
+See [go.opentelemetry.io/otel/sdk/log/internal/x] for information about the
+experimental features.
 */
 package log // import "go.opentelemetry.io/otel/sdk/log"

sdk/log/example_test.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"fmt"
 	"strings"
+	"sync"
 
 	logapi "go.opentelemetry.io/otel/log"
 	"go.opentelemetry.io/otel/log/global"
@@ -58,7 +59,7 @@ func ExampleProcessor_filtering() {
 	// Wrap the processor so that it ignores processing log records
 	// when a context deriving from WithIgnoreLogs is passed
 	// to the logging methods.
-	processor = &ContextFilterProcessor{processor}
+	processor = &ContextFilterProcessor{Processor: processor}
 
 	// The created processor can then be registered with
 	// the OpenTelemetry Logs SDK using the WithProcessor option.
@@ -81,6 +82,15 @@ func WithIgnoreLogs(ctx context.Context) context.Context {
 // [WithIgnoreLogs] is passed to its methods.
 type ContextFilterProcessor struct {
 	log.Processor
+
+	lazyFilter sync.Once
+	// Use the experimental FilterProcessor interface
+	// (go.opentelemetry.io/otel/sdk/log/internal/x).
+	filter filter
+}
+
+type filter interface {
+	Enabled(ctx context.Context, record log.Record) bool
 }
 
 func (p *ContextFilterProcessor) OnEmit(ctx context.Context, record *log.Record) error {
@@ -91,7 +101,12 @@ func (p *ContextFilterProcessor) OnEmit(ctx context.Context, record *log.Record)
 }
 
 func (p *ContextFilterProcessor) Enabled(ctx context.Context, record log.Record) bool {
-	return !ignoreLogs(ctx) && p.Processor.Enabled(ctx, record)
+	p.lazyFilter.Do(func() {
+		if f, ok := p.Processor.(filter); ok {
+			p.filter = f
+		}
+	})
+	return !ignoreLogs(ctx) && (p.filter == nil || p.filter.Enabled(ctx, record))
 }
 
 func ignoreLogs(ctx context.Context) bool {

sdk/log/internal/x/README.md

@@ -0,0 +1,35 @@
+# Experimental Features
+
+The Logs SDK contains features that have not yet stabilized.
+These features are added to the OpenTelemetry Go Logs SDK prior to stabilization so that users can start experimenting with them and provide feedback.
+
+These feature may change in backwards incompatible ways as feedback is applied.
+See the [Compatibility and Stability](#compatibility-and-stability) section for more information.
+
+## Features
+
+- [Filter Processors](#filter-processor)
+
+### Filter Processor
+
+Users of logging libraries often want to know if a log `Record` will be processed or dropped before they perform complex operations to construct the `Record`.
+The [`Logger`] in the Logs Bridge API provides the `Enabled` method for just this use-case.
+In order for the Logs Bridge SDK to effectively implement this API, it needs to be known if the registered [`Processor`]s are enabled for the `Record` within a context.
+A [`Processor`] that knows, and can identify, what `Record` it will process or drop when it is passed to `OnEmit` can communicate this to the SDK `Logger` by implementing the `FilterProcessor`.
+
+By default, the SDK `Logger.Enabled` will return true when called.
+Only if all the registered [`Processor`]s implement `FilterProcessor` and they all return `false` will `Logger.Enabled` return `false`.
+
+See the [`minsev`] [`Processor`] for an example use-case.
+It is used to filter `Record`s out that a have a `Severity` below a threshold.
+
+[`Logger`]: https://pkg.go.dev/go.opentelemetry.io/otel/log#Logger
+[`Processor`]: https://pkg.go.dev/go.opentelemetry.io/otel/sdk/log#Processor
+[`minsev`]: https://pkg.go.dev/go.opentelemetry.io/contrib/processors/minsev
+
+## Compatibility and Stability
+
+Experimental features do not fall within the scope of the OpenTelemetry Go versioning and stability [policy](../../../../VERSIONING.md).
+These features may be removed or modified in successive version releases, including patch versions.
+
+When an experimental feature is promoted to a stable feature, a migration path will be included in the changelog entry of the release.

sdk/log/internal/x/x.go

@@ -0,0 +1,46 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// Package x contains support for Logs SDK experimental features.
+package x // import "go.opentelemetry.io/otel/sdk/log/internal/x"
+
+import (
+	"context"
+
+	"go.opentelemetry.io/otel/log"
+)
+
+// FilterProcessor is a [Processor] that knows, and can identify, what
+// [log.Record] it will process or drop when it is passed to OnEmit.
+//
+// This is useful for users of logging libraries that want to know if a [log.Record]
+// will be processed or dropped before they perform complex operations to
+// construct the [log.Record].
+//
+// [Processor] implementations that choose to support this by satisfying this
+// interface are expected to re-evaluate the [log.Record]s passed to OnEmit, it is
+// not expected that the caller to OnEmit will use the functionality from this
+// interface prior to calling OnEmit.
+//
+// This should only be implemented for [Processor]s that can make reliable
+// enough determination of this prior to processing a [log.Record] and where
+// the result is dynamic.
+//
+// [Processor]: https://pkg.go.dev/go.opentelemetry.io/otel/sdk/log#Processor
+type FilterProcessor interface {
+	// Enabled returns whether the Processor will process for the given context
+	// and record.
+	//
+	// The passed record is likely to be a partial record with only the
+	// bridge-relevant information being provided (e.g a record with only the
+	// Severity set). If a Logger needs more information than is provided, it
+	// is said to be in an indeterminate state (see below).
+	//
+	// The returned value will be true when the Processor will process for the
+	// provided context and record, and will be false if the Processor will not
+	// process. An implementation should default to returning true for an
+	// indeterminate state.
+	//
+	// Implementations should not modify the record.
+	Enabled(ctx context.Context, record log.Record) bool
+}

sdk/log/logger.go

@@ -11,6 +11,7 @@ import (
 	"go.opentelemetry.io/otel/log"
 	"go.opentelemetry.io/otel/log/embedded"
 	"go.opentelemetry.io/otel/sdk/instrumentation"
+	"go.opentelemetry.io/otel/sdk/log/internal/x"
 	"go.opentelemetry.io/otel/trace"
 )
 
@@ -42,13 +43,30 @@ func (l *logger) Emit(ctx context.Context, r log.Record) {
 	}
 }
 
-func (l *logger) Enabled(ctx context.Context, r log.Record) bool {
-	newRecord := l.newRecord(ctx, r)
-	for _, p := range l.provider.processors {
-		if enabled := p.Enabled(ctx, newRecord); enabled {
+// Enabled returns true if at least one Processor held by the LoggerProvider
+// that created the logger will process the record for the provided context.
+//
+// If it is not possible to definitively determine the record will be
+// processed, true will be returned by default. A value of false will only be
+// returned if it can be positively verified that no Processor will process the
+// record.
+func (l *logger) Enabled(ctx context.Context, record log.Record) bool {
+	fltrs := l.provider.filterProcessors()
+	// If there are more Processors than FilterProcessors we cannot be sure
+	// that all Processors will drop the record. Therefore, return true.
+	//
+	// If all Processors are FilterProcessors, check if any is enabled.
+	return len(l.provider.processors) > len(fltrs) || anyEnabled(ctx, record, fltrs)
+}
+
+func anyEnabled(ctx context.Context, r log.Record, fltrs []x.FilterProcessor) bool {
+	for _, f := range fltrs {
+		if f.Enabled(ctx, r) {
+			// At least one Processor will process the Record.
 			return true
 		}
 	}
+	// No Processor will process the record
 	return false
 }
 

sdk/log/logger_test.go

@@ -215,8 +215,9 @@ func TestLoggerEmit(t *testing.T) {
 }
 
 func TestLoggerEnabled(t *testing.T) {
-	p0, p1, p2WithDisabled := newProcessor("0"), newProcessor("1"), newProcessor("2")
-	p2WithDisabled.enabled = false
+	p0 := newFltrProcessor("0", true)
+	p1 := newFltrProcessor("1", true)
+	p2WithDisabled := newFltrProcessor("2", false)
 
 	testCases := []struct {
 		name     string
@@ -273,3 +274,24 @@ func TestLoggerEnabled(t *testing.T) {
 		})
 	}
 }
+
+func BenchmarkLoggerEnabled(b *testing.B) {
+	provider := NewLoggerProvider(
+		WithProcessor(newFltrProcessor("0", false)),
+		WithProcessor(newFltrProcessor("1", true)),
+	)
+	logger := provider.Logger("BenchmarkLoggerEnabled")
+	ctx, r := context.Background(), log.Record{}
+	r.SetSeverityText("test")
+
+	var enabled bool
+
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for n := 0; n < b.N; n++ {
+		enabled = logger.Enabled(ctx, r)
+	}
+
+	_ = enabled
+}

sdk/log/processor.go

@@ -12,6 +12,9 @@ import (
 // Any of the Processor's methods may be called concurrently with itself
 // or with other methods. It is the responsibility of the Processor to manage
 // this concurrency.
+//
+// See [go.opentelemetry.io/otel/sdk/log/internal/x] for information about how
+// a Processor can be extended to support experimental features.
 type Processor interface {
 	// OnEmit is called when a Record is emitted.
 	//
@@ -35,27 +38,6 @@ type Processor interface {
 	// to create a copy that shares no state with the original.
 	OnEmit(ctx context.Context, record *Record) error
 
-	// Enabled returns whether the Processor will process for the given context
-	// and record.
-	//
-	// The passed record is likely to be a partial record with only the
-	// bridge-relevant information being provided (e.g a record with only the
-	// Severity set). If a Logger needs more information than is provided, it
-	// is said to be in an indeterminate state (see below).
-	//
-	// The returned value will be true when the Processor will process for the
-	// provided context and record, and will be false if the Processor will not
-	// process. The returned value may be true or false in an indeterminate
-	// state. An implementation should default to returning true for an
-	// indeterminate state, but may return false if valid reasons in particular
-	// circumstances exist (e.g. performance, correctness).
-	//
-	// The SDK invokes the processors sequentially in the same order as
-	// they were registered using [WithProcessor] until any processor returns true.
-	//
-	// Implementations should not modify the record.
-	Enabled(ctx context.Context, record Record) bool
-
 	// Shutdown is called when the SDK shuts down. Any cleanup or release of
 	// resources held by the exporter should be done in this call.
 	//

sdk/log/provider.go

@@ -14,6 +14,7 @@ import (
 	"go.opentelemetry.io/otel/log/embedded"
 	"go.opentelemetry.io/otel/log/noop"
 	"go.opentelemetry.io/otel/sdk/instrumentation"
+	"go.opentelemetry.io/otel/sdk/log/internal/x"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
 
@@ -65,6 +66,9 @@ type LoggerProvider struct {
 	attributeCountLimit       int
 	attributeValueLengthLimit int
 
+	fltrProcessorsOnce sync.Once
+	fltrProcessors     []x.FilterProcessor
+
 	loggersMu sync.Mutex
 	loggers   map[instrumentation.Scope]*logger
 
@@ -92,6 +96,17 @@ func NewLoggerProvider(opts ...LoggerProviderOption) *LoggerProvider {
 	}
 }
 
+func (p *LoggerProvider) filterProcessors() []x.FilterProcessor {
+	p.fltrProcessorsOnce.Do(func() {
+		for _, proc := range p.processors {
+			if f, ok := proc.(x.FilterProcessor); ok {
+				p.fltrProcessors = append(p.fltrProcessors, f)
+			}
+		}
+	})
+	return p.fltrProcessors
+}
+
 // Logger returns a new [log.Logger] with the provided name and configuration.
 //
 // If p is shut down, a [noop.Logger] instance is returned.