RUM-8448 Add ios.benchmark.batch_count

Author: maxep

BenchmarkTests/Runner/BenchmarkMeter.swift

@@ -68,6 +68,10 @@ internal final class Meter: DatadogInternal.BenchmarkMeter {
     func gauge(metric: @autoclosure () -> String) -> DatadogInternal.BenchmarkGauge {
         meter.createDoubleMeasure(name: metric())
     }
+
+    func observe(metric: @autoclosure () -> String, callback: @escaping (any DatadogInternal.BenchmarkGauge) -> Void) {
+        _ = meter.createDoubleObserver(name: metric()) { callback(DoubleObserverWrapper(observer: $0)) }
+    }
 }
 
 extension AnyCounterMetric<Double>: DatadogInternal.BenchmarkCounter {
@@ -81,3 +85,11 @@ extension AnyMeasureMetric<Double>: DatadogInternal.BenchmarkGauge {
         record(value: value, labelset: LabelSet(labels: attributes()))
     }
 }
+
+private struct DoubleObserverWrapper: DatadogInternal.BenchmarkGauge {
+    let observer: DoubleObserverMetric
+
+    func record(value: Double, attributes: @autoclosure () -> [String: String]) {
+        observer.observe(value: value, labelset: LabelSet(labels: attributes()))
+    }
+}

DatadogCore/Sources/Core/Storage/FilesOrchestrator.swift

@@ -80,6 +80,15 @@ internal class FilesOrchestrator: FilesOrchestratorType {
         self.dateProvider = dateProvider
         self.telemetry = telemetry
         self.metricsData = metricsData
+
+#if DD_BENCHMARK
+        bench.meter.observe(metric: "ios.benchmark.batch_count") {[weak self] gauge in
+            if let self {
+                let files = try? directory.files()
+                files.map { gauge.record($0.count, attributes: ["track": self.trackName]) }
+            }
+        }
+#endif
     }
 
     // MARK: - `WritableFile` orchestration

DatadogInternal/Sources/Benchmarks/BenchmarkProfiler.swift

@@ -56,6 +56,8 @@ public protocol BenchmarkMeter {
     /// - Parameter metric: The metric name.
     /// - Returns: The gauge instance.
     func gauge(metric: @autoclosure () -> String) -> BenchmarkGauge
+
+    func observe(metric: @autoclosure () -> String, callback: @escaping (BenchmarkGauge) -> Void )
 }
 
 /// The Benchmark Tracer will create and start spans in a benchmark environment.
@@ -137,6 +139,8 @@ private final class NOPBench: BenchmarkProfiler, BenchmarkTracer, BenchmarkSpan,
     /// no-op
     func gauge(metric: @autoclosure () -> String) -> BenchmarkGauge { self }
     /// no-op
+    func observe(metric: @autoclosure () -> String, callback: @escaping (any BenchmarkGauge) -> Void) { }
+    /// no-op
     func add(value: Double, attributes: @autoclosure () -> [String: String]) { }
     /// no-op
     func record(value: Double, attributes: @autoclosure () -> [String: String]) { }