pprofile: introduce SetStack helper method (#14007)

This introduces the `SetStack` helper method for pprofile, as we already
have `SetFunction`, `SetMapping`, `SetString`, ...

This is needed to help with setting up merging of profiles.
#13106

---------

Co-authored-by: Alex Boten <[email protected]>

Author: dmathieu

.chloggen/pprofile-set-stack.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: pdata/pprofile
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Introduce `SetStack` method
+
+# One or more tracking issues or pull requests related to the change
+issues: [14007]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [api]

pdata/pprofile/stacks.go

@@ -0,0 +1,31 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package pprofile // import "go.opentelemetry.io/collector/pdata/pprofile"
+
+import (
+	"errors"
+	"math"
+)
+
+var errTooManyStackTableEntries = errors.New("too many entries in StackTable")
+
+// SetStack updates a StackSlice, adding or providing a stack and returns its
+// index.
+func SetStack(table StackSlice, st Stack) (int32, error) {
+	for j, l := range table.All() {
+		if l.Equal(st) {
+			if j > math.MaxInt32 {
+				return 0, errTooManyStackTableEntries
+			}
+			return int32(j), nil //nolint:gosec // G115 overflow checked
+		}
+	}
+
+	if table.Len() >= math.MaxInt32 {
+		return 0, errTooManyStackTableEntries
+	}
+
+	st.CopyTo(table.AppendEmpty())
+	return int32(table.Len() - 1), nil //nolint:gosec // G115 overflow checked
+}

pdata/pprofile/stacks_test.go

@@ -0,0 +1,115 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package pprofile
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSetStack(t *testing.T) {
+	table := NewStackSlice()
+	s := NewStack()
+	s.LocationIndices().Append(1)
+	s2 := NewStack()
+	s.LocationIndices().Append(2)
+
+	// Put a first stack
+	idx, err := SetStack(table, s)
+	require.NoError(t, err)
+	assert.Equal(t, 1, table.Len())
+	assert.Equal(t, int32(0), idx)
+
+	// Put the same stack
+	// This should be a no-op.
+	idx, err = SetStack(table, s)
+	require.NoError(t, err)
+	assert.Equal(t, 1, table.Len())
+	assert.Equal(t, int32(0), idx)
+
+	// Set a new stack
+	// This sets the index and adds to the table.
+	idx, err = SetStack(table, s2)
+	require.NoError(t, err)
+	assert.Equal(t, 2, table.Len())
+	assert.Equal(t, int32(table.Len()-1), idx) //nolint:gosec // G115
+
+	// Set an existing stack
+	idx, err = SetStack(table, s)
+	require.NoError(t, err)
+	assert.Equal(t, 2, table.Len())
+	assert.Equal(t, int32(0), idx)
+	// Set another existing stack
+	idx, err = SetStack(table, s2)
+	require.NoError(t, err)
+	assert.Equal(t, 2, table.Len())
+	assert.Equal(t, int32(table.Len()-1), idx) //nolint:gosec // G115
+}
+
+func BenchmarkSetStack(b *testing.B) {
+	for _, bb := range []struct {
+		name  string
+		stack Stack
+
+		runBefore func(*testing.B, StackSlice)
+	}{
+		{
+			name:  "with a new stack",
+			stack: NewStack(),
+		},
+		{
+			name: "with an existing stack",
+			stack: func() Stack {
+				s := NewStack()
+				s.LocationIndices().Append(1)
+				return s
+			}(),
+
+			runBefore: func(_ *testing.B, table StackSlice) {
+				s := table.AppendEmpty()
+				s.LocationIndices().Append(1)
+			},
+		},
+		{
+			name:  "with a duplicate stack",
+			stack: NewStack(),
+
+			runBefore: func(_ *testing.B, table StackSlice) {
+				_, err := SetStack(table, NewStack())
+				require.NoError(b, err)
+			},
+		},
+		{
+			name: "with a hundred stacks to loop through",
+			stack: func() Stack {
+				s := NewStack()
+				s.LocationIndices().Append(1)
+				return s
+			}(),
+
+			runBefore: func(_ *testing.B, table StackSlice) {
+				for range 100 {
+					table.AppendEmpty()
+				}
+			},
+		},
+	} {
+		b.Run(bb.name, func(b *testing.B) {
+			table := NewStackSlice()
+
+			if bb.runBefore != nil {
+				bb.runBefore(b, table)
+			}
+
+			b.ResetTimer()
+			b.ReportAllocs()
+
+			for b.Loop() {
+				_, _ = SetStack(table, bb.stack)
+			}
+		})
+	}
+}