pdh: report duplicate instances by occurrence instead of renaming them (#2742)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

internal/pdh/occurrence.go

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: Apache-2.0
+//
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build windows
+
+package pdh
+
+import "strconv"
+
+// SuffixDuplicates makes the names of rows unique within a sample for
+// collectors that publish every occurrence of a duplicate instance name.
+//
+// name returns a pointer to the name of a row, occurrence its Occurrence (see
+// [NewCollector]). The first occurrence keeps its name. Later occurrences get
+// the suffix "#N", where N counts from 1 and skips every N for which
+// "<name>#N" is the name of another row, for example a suffix that Windows
+// added itself. Only the names of rows reserve suffixes: an instance that
+// Windows reported without valid data has no row and reserves nothing. N
+// depends on the order of the sample and is not a stable identity.
+//
+// Collectors can map names, e.g. an empty name to a placeholder, before they
+// call SuffixDuplicates, so that the suffix is added to the published name.
+func SuffixDuplicates[T any](rows []T, name func(*T) *string, occurrence func(*T) int) {
+	var names map[string]struct{}
+
+	for i := range rows {
+		if occurrence(&rows[i]) == 0 {
+			continue
+		}
+
+		if names == nil {
+			names = make(map[string]struct{}, len(rows))
+
+			for j := range rows {
+				names[*name(&rows[j])] = struct{}{}
+			}
+		}
+
+		instanceName := name(&rows[i])
+		base := *instanceName
+		remaining := occurrence(&rows[i])
+
+		for suffix := 1; ; suffix++ {
+			candidate := base + "#" + strconv.Itoa(suffix)
+			if _, literal := names[candidate]; literal {
+				continue
+			}
+
+			remaining--
+			if remaining == 0 {
+				*instanceName = candidate
+
+				break
+			}
+		}
+	}
+}