added metrics for drop and export Span processor

Sources/OpenTelemetryApi/Metrics/Stable/DefaultStableMeter.swift

@@ -60,7 +60,15 @@ public class DefaultStableMeter : StableMeter {
     }
   }
 
-  private class NoopLongGaugeBuilder : LongGaugeBuilder {
+    private class NoopLongGaugeBuilder : LongGaugeBuilder {
+        func setUnit(_ unit: String) -> any LongGaugeBuilder {
+            self
+        }
+
+        func setDescription(_ description: String) -> any LongGaugeBuilder {
+            self
+        }
+
     func buildWithCallback(_ callback: @escaping (ObservableLongMeasurement) -> Void) -> ObservableLongGauge {
         NoopObservableLongGauge()
     }
@@ -123,7 +131,15 @@ public class DefaultStableMeter : StableMeter {
     func add(value: Int, attribute: [String : AttributeValue]) {}
   }
 
-  private class NoopLongCounterBuilder : LongCounterBuilder {
+    private class NoopLongCounterBuilder : LongCounterBuilder {
+        func setUnit(_ unit: String) -> any LongCounterBuilder {
+            self
+        }
+
+        func setDescription(_ description: String) -> any LongCounterBuilder {
+            self
+        }
+
     func ofDoubles() -> DoubleCounterBuilder {
       NoopDoubleCounterBuilder()
     }

Sources/OpenTelemetryApi/Metrics/Stable/DefaultStableMeterProvider.swift

@@ -8,6 +8,8 @@ import Foundation
 public class DefaultStableMeterProvider: StableMeterProvider {
   static let noopMeterBuilder = NoopMeterBuilder()
 
+    public init() {}
+
   public static func noop() -> MeterBuilder {
     noopMeterBuilder
   }

Sources/OpenTelemetryApi/Metrics/Stable/LongCounterBuilder.swift

@@ -6,6 +6,8 @@
 import Foundation
 
 public protocol LongCounterBuilder : AnyObject {
+    func setUnit(_ unit: String) -> LongCounterBuilder
+    func setDescription(_ description: String) -> LongCounterBuilder
     func ofDoubles() -> DoubleCounterBuilder
     func build() -> LongCounter
     func buildWithCallback(_ callback: @escaping (ObservableLongMeasurement) -> Void) -> ObservableLongCounter

Sources/OpenTelemetryApi/Metrics/Stable/LongGaugeBuilder.swift

@@ -6,5 +6,7 @@
 import Foundation
 
 public protocol LongGaugeBuilder : AnyObject {
+    func setUnit(_ unit: String) -> LongGaugeBuilder
+    func setDescription(_ description: String) -> LongGaugeBuilder
     func buildWithCallback(_ callback: @escaping (ObservableLongMeasurement) -> Void) -> ObservableLongGauge
 }

Sources/OpenTelemetrySdk/Metrics/Stable/LongCounterMeterBuilderSdk.swift

@@ -41,4 +41,14 @@ public class LongCounterMeterBuilderSdk: LongCounterBuilder, InstrumentBuilder {
         -> OpenTelemetryApi.ObservableLongCounter {
         registerLongAsynchronousInstrument(type: .observableCounter, updater: callback)
     }
+
+    public func setDescription(_ description: String) -> LongCounterBuilder {
+        self.description = description
+        return self
+    }
+
+    public func setUnit(_ unit: String) -> LongCounterBuilder {
+        self.unit = unit
+        return self
+    }
 }

Sources/OpenTelemetrySdk/Metrics/Stable/LongGaugeBuilderSdk.swift

@@ -34,7 +34,13 @@ public class LongGaugeBuilderSdk : LongGaugeBuilder, InstrumentBuilder {
         registerLongAsynchronousInstrument(type: type, updater: callback)
     }
 
-
-
+    public func setDescription(_ description: String) -> LongGaugeBuilder {
+        self.description = description
+        return self
+    }
 
+    public func setUnit(_ unit: String) -> LongGaugeBuilder {
+        self.unit = unit
+        return self
+    }
 }

Sources/OpenTelemetrySdk/Trace/SpanProcessors/BatchSpanProcessor.swift

@@ -15,21 +15,36 @@ import OpenTelemetryApi
 /// exports the spans to wake up and start a new export cycle.
 /// This batchSpanProcessor can cause high contention in a very high traffic service.
 public struct BatchSpanProcessor: SpanProcessor {
+    fileprivate static let SPAN_PROCESSOR_TYPE_LABEL: String = "processorType"
+    fileprivate static let SPAN_PROCESSOR_DROPPED_LABEL: String = "dropped"
+    fileprivate static let SPAN_PROCESSOR_TYPE_VALUE: String = BatchSpanProcessor.name
+
+    fileprivate var worker: BatchWorker
 
-
-  fileprivate var worker: BatchWorker
-
-  public init(spanExporter: SpanExporter, scheduleDelay: TimeInterval = 5, exportTimeout: TimeInterval = 30,
-              maxQueueSize: Int = 2048, maxExportBatchSize: Int = 512, willExportCallback: ((inout [SpanData]) -> Void)? = nil)
-  {
-    worker = BatchWorker(spanExporter: spanExporter,
-                         scheduleDelay: scheduleDelay,
-                         exportTimeout: exportTimeout,
-                         maxQueueSize: maxQueueSize,
-                         maxExportBatchSize: maxExportBatchSize,
-                         willExportCallback: willExportCallback)
-    worker.start()
-  }
+    public static var name: String {
+        String(describing: Self.self)
+    }
+
+    public init(
+        spanExporter: SpanExporter,
+        meterProvider: StableMeterProvider,
+        scheduleDelay: TimeInterval = 5,
+        exportTimeout: TimeInterval = 30,
+        maxQueueSize: Int = 2048,
+        maxExportBatchSize: Int = 512,
+        willExportCallback: ((inout [SpanData]) -> Void)? = nil
+    ) {
+        worker = BatchWorker(
+            spanExporter: spanExporter,
+            meterProvider: meterProvider,
+            scheduleDelay: scheduleDelay,
+            exportTimeout: exportTimeout,
+            maxQueueSize: maxQueueSize,
+            maxExportBatchSize: maxExportBatchSize,
+            willExportCallback: willExportCallback
+        )
+        worker.start()
+    }
 
   public let isStartRequired = false
   public let isEndRequired = true
@@ -57,36 +72,77 @@ public struct BatchSpanProcessor: SpanProcessor {
 /// the data.
 /// The list of batched data is protected by a NSCondition which ensures full concurrency.
 private class BatchWorker: Thread {
-  let spanExporter: SpanExporter
-  let scheduleDelay: TimeInterval
-  let maxQueueSize: Int
-  let exportTimeout: TimeInterval
-  let maxExportBatchSize: Int
-  let willExportCallback: ((inout [SpanData]) -> Void)?
-  let halfMaxQueueSize: Int
-  private let cond = NSCondition()
-  var spanList = [ReadableSpan]()
-  var queue: OperationQueue
-
-  init(spanExporter: SpanExporter, scheduleDelay: TimeInterval, exportTimeout: TimeInterval, maxQueueSize: Int, maxExportBatchSize: Int, willExportCallback: ((inout [SpanData]) -> Void)?) {
-    self.spanExporter = spanExporter
-    self.scheduleDelay = scheduleDelay
-    self.exportTimeout = exportTimeout
-    self.maxQueueSize = maxQueueSize
-    halfMaxQueueSize = maxQueueSize >> 1
-    self.maxExportBatchSize = maxExportBatchSize
-    self.willExportCallback = willExportCallback
-    queue = OperationQueue()
-    queue.name = "BatchWorker Queue"
-    queue.maxConcurrentOperationCount = 1
-  }
+    let spanExporter: SpanExporter
+    let meterProvider: StableMeterProvider
+    let scheduleDelay: TimeInterval
+    let maxQueueSize: Int
+    let exportTimeout: TimeInterval
+    let maxExportBatchSize: Int
+    let willExportCallback: ((inout [SpanData]) -> Void)?
+    let halfMaxQueueSize: Int
+    private let cond = NSCondition()
+    var spanList = [ReadableSpan]()
+    var queue: OperationQueue
+
+    private var queueSizeGauge: ObservableLongGauge?
+    private var processedSpansCounter: LongCounter
+    private let droppedAttrs: [String: AttributeValue]
+    private let exportedAttrs: [String: AttributeValue]
+    init(
+        spanExporter: SpanExporter,
+        meterProvider: StableMeterProvider,
+        scheduleDelay: TimeInterval,
+        exportTimeout: TimeInterval,
+        maxQueueSize: Int,
+        maxExportBatchSize: Int,
+        willExportCallback: ((inout [SpanData]) -> Void)?
+    ) {
+        self.spanExporter = spanExporter
+        self.meterProvider = meterProvider
+        self.scheduleDelay = scheduleDelay
+        self.exportTimeout = exportTimeout
+        self.maxQueueSize = maxQueueSize
+        halfMaxQueueSize = maxQueueSize >> 1
+        self.maxExportBatchSize = maxExportBatchSize
+        self.willExportCallback = willExportCallback
+        queue = OperationQueue()
+        queue.name = "BatchWorker Queue"
+        queue.maxConcurrentOperationCount = 1
+
+        let meter = meterProvider.meterBuilder(name: "io.opentelemetry.sdk.trace").build()
+        self.queueSizeGauge = meter.gaugeBuilder(name: "queueSize")
+            .ofLongs()
+            .setDescription("The number of items queued")
+            .setUnit("1")
+            .buildWithCallback { result in
+                result.record(
+                    value: maxQueueSize,
+                    attributes: [
+                        BatchSpanProcessor.SPAN_PROCESSOR_TYPE_LABEL: .string(BatchSpanProcessor.SPAN_PROCESSOR_TYPE_VALUE)
+                    ]
+                )
+            }
+
+        processedSpansCounter = meter.counterBuilder(name: "processedSpans")
+            .setUnit("1")
+            .setDescription("The number of spans processed by the BatchSpanProcessor. [dropped=true if they were dropped due to high throughput]")
+            .build()
+        droppedAttrs = [
+            BatchSpanProcessor.SPAN_PROCESSOR_TYPE_LABEL: .string(BatchSpanProcessor.SPAN_PROCESSOR_TYPE_VALUE),
+            BatchSpanProcessor.SPAN_PROCESSOR_DROPPED_LABEL: .bool(true)
+        ]
+        exportedAttrs = [
+            BatchSpanProcessor.SPAN_PROCESSOR_TYPE_LABEL: .string(BatchSpanProcessor.SPAN_PROCESSOR_TYPE_VALUE),
+            BatchSpanProcessor.SPAN_PROCESSOR_DROPPED_LABEL: .bool(false)
+        ]
+    }
 
   func addSpan(span: ReadableSpan) {
     cond.lock()
     defer { cond.unlock() }
 
     if spanList.count == maxQueueSize {
-      // TODO: Record a counter for dropped spans.
+        processedSpansCounter.add(value: 1, attribute: droppedAttrs)
       return
     }
     // TODO: Record a gauge for referenced spans.
@@ -148,11 +204,16 @@ private class BatchWorker: Thread {
     timeoutTimer.cancel()
   }
 
-  private func exportAction(spanList: [ReadableSpan], explicitTimeout: TimeInterval? = nil) {
-    stride(from: 0, to: spanList.endIndex, by: maxExportBatchSize).forEach {
-      var spansToExport = spanList[$0 ..< min($0 + maxExportBatchSize, spanList.count)].map { $0.toSpanData() }
-      willExportCallback?(&spansToExport)
-      spanExporter.export(spans: spansToExport, explicitTimeout: explicitTimeout)
+    private func exportAction(spanList: [ReadableSpan], explicitTimeout: TimeInterval? = nil) {
+        stride(from: 0, to: spanList.endIndex, by: maxExportBatchSize).forEach {
+            var spansToExport = spanList[$0 ..< min($0 + maxExportBatchSize, spanList.count)].map { $0.toSpanData() }
+            willExportCallback?(&spansToExport)
+            let result = spanExporter.export(spans: spansToExport, explicitTimeout: explicitTimeout)
+            if result == .success {
+                cond.lock()
+                processedSpansCounter.add(value: spanList.count, attribute: exportedAttrs)
+                cond.unlock()
+            }
+        }
     }
-  }
 }

Tests/OpenTelemetrySdkTests/Trace/Export/BatchSpansProcessorTests.swift

@@ -44,15 +44,22 @@ class BatchSpansProcessorTests: XCTestCase {
   }
 
   func testStartEndRequirements() {
-    let spansProcessor = BatchSpanProcessor(spanExporter: WaitingSpanExporter(numberToWaitFor: 0))
+      let spansProcessor = BatchSpanProcessor(
+        spanExporter: WaitingSpanExporter(numberToWaitFor: 0),
+        meterProvider: DefaultStableMeterProvider()
+      )
     XCTAssertFalse(spansProcessor.isStartRequired)
     XCTAssertTrue(spansProcessor.isEndRequired)
   }
 
   func testExportDifferentSampledSpans() {
     let waitingSpanExporter = WaitingSpanExporter(numberToWaitFor: 2)
 
-    tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(spanExporter: waitingSpanExporter, scheduleDelay: maxScheduleDelay))
+    tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(
+        spanExporter: waitingSpanExporter,
+        meterProvider: DefaultStableMeterProvider(),
+        scheduleDelay: maxScheduleDelay)
+    )
     let span1 = createSampledEndedSpan(spanName: spanName1)
     let span2 = createSampledEndedSpan(spanName: spanName2)
     let exported = waitingSpanExporter.waitForExport()
@@ -63,7 +70,12 @@ class BatchSpansProcessorTests: XCTestCase {
   func testExportMoreSpansThanTheBufferSize() {
     let waitingSpanExporter = WaitingSpanExporter(numberToWaitFor: 6)
 
-    tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(spanExporter: waitingSpanExporter, scheduleDelay: maxScheduleDelay, maxQueueSize: 6, maxExportBatchSize: 2))
+    tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(
+        spanExporter: waitingSpanExporter,
+        meterProvider: DefaultStableMeterProvider(),
+        scheduleDelay: maxScheduleDelay,
+        maxQueueSize: 6, maxExportBatchSize: 2)
+    )
 
     let span1 = createSampledEndedSpan(spanName: spanName1)
     let span2 = createSampledEndedSpan(spanName: spanName1)
@@ -82,7 +94,13 @@ class BatchSpansProcessorTests: XCTestCase {
 
   func testForceExport() {
     let waitingSpanExporter = WaitingSpanExporter(numberToWaitFor: 1)
-    let batchSpansProcessor = BatchSpanProcessor(spanExporter: waitingSpanExporter, scheduleDelay: 10, maxQueueSize: 10000, maxExportBatchSize: 2000)
+    let batchSpansProcessor = BatchSpanProcessor(
+        spanExporter: waitingSpanExporter,
+        meterProvider: DefaultStableMeterProvider(),
+        scheduleDelay: 10,
+        maxQueueSize: 10000,
+        maxExportBatchSize: 2000
+    )
     tracerSdkFactory.addSpanProcessor(batchSpansProcessor)
 
     for _ in 0 ..< 100 {
@@ -96,7 +114,10 @@ class BatchSpansProcessorTests: XCTestCase {
   func testExportSpansToMultipleServices() {
     let waitingSpanExporter = WaitingSpanExporter(numberToWaitFor: 2)
     let waitingSpanExporter2 = WaitingSpanExporter(numberToWaitFor: 2)
-    tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(spanExporter: MultiSpanExporter(spanExporters: [waitingSpanExporter, waitingSpanExporter2]), scheduleDelay: maxScheduleDelay))
+    tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(
+        spanExporter: MultiSpanExporter(spanExporters: [waitingSpanExporter, waitingSpanExporter2]),
+        meterProvider: DefaultStableMeterProvider(),
+        scheduleDelay: maxScheduleDelay))
 
     let span1 = createSampledEndedSpan(spanName: spanName1)
     let span2 = createSampledEndedSpan(spanName: spanName2)
@@ -110,7 +131,13 @@ class BatchSpansProcessorTests: XCTestCase {
     let maxQueuedSpans = 8
     let waitingSpanExporter = WaitingSpanExporter(numberToWaitFor: maxQueuedSpans)
 
-    tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(spanExporter: MultiSpanExporter(spanExporters: [waitingSpanExporter, blockingSpanExporter]), scheduleDelay:    maxScheduleDelay, maxQueueSize: maxQueuedSpans, maxExportBatchSize: maxQueuedSpans / 2))
+    tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(
+        spanExporter: MultiSpanExporter(spanExporters: [waitingSpanExporter, blockingSpanExporter]),
+        meterProvider: DefaultStableMeterProvider(),
+        scheduleDelay:    maxScheduleDelay,
+        maxQueueSize: maxQueuedSpans,
+        maxExportBatchSize: maxQueuedSpans / 2)
+    )
 
     var spansToExport = [SpanData]()
     // Wait to block the worker thread in the BatchSampledSpansProcessor. This ensures that no items
@@ -162,7 +189,11 @@ class BatchSpansProcessorTests: XCTestCase {
   func testExportNotSampledSpans() {
     let waitingSpanExporter = WaitingSpanExporter(numberToWaitFor: 1)
 
-    tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(spanExporter: waitingSpanExporter, scheduleDelay: maxScheduleDelay))
+    tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(
+        spanExporter: waitingSpanExporter,
+        meterProvider: DefaultStableMeterProvider(),
+        scheduleDelay: maxScheduleDelay)
+    )
 
     createNotSampledEndedSpan(spanName: spanName1)
     createNotSampledEndedSpan(spanName: spanName2)
@@ -181,7 +212,11 @@ class BatchSpansProcessorTests: XCTestCase {
     let waitingSpanExporter = WaitingSpanExporter(numberToWaitFor: 1)
 
     // Set the export delay to zero, for no timeout, in order to confirm the #flush() below works
-      tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(spanExporter: waitingSpanExporter, scheduleDelay: 0.1))
+      tracerSdkFactory.addSpanProcessor(BatchSpanProcessor(
+        spanExporter: waitingSpanExporter,
+        meterProvider: DefaultStableMeterProvider(),
+        scheduleDelay: 0.1)
+      )
 
     let span2 = createSampledEndedSpan(spanName: spanName2)