Synchronize access race in HistogramMetric

Sources/OpenTelemetrySdk/Metrics/HistogramMetricSdk.swift

@@ -10,19 +10,23 @@ internal class HistogramMetricSdk<T: SignedNumeric & Comparable>: HistogramMetri
     public private(set) var boundInstruments = [LabelSet: BoundHistogramMetricSdkBase<T>]()
     let metricName: String
     let explicitBoundaries: Array<T>?
+    let bindUnbindLock = Lock()
 
     init(name: String, explicitBoundaries: Array<T>? = nil) {
         metricName = name
         self.explicitBoundaries = explicitBoundaries
     }
 
     func bind(labelset: LabelSet) -> BoundHistogramMetric<T> {
-        var boundInstrument = boundInstruments[labelset]
-        if boundInstrument == nil {
-            boundInstrument = createMetric()
-            boundInstruments[labelset] = boundInstrument!
+        bindUnbindLock.withLock {
+            var boundInstrument = boundInstruments[labelset]
+            if boundInstrument == nil {
+                boundInstrument = createMetric()
+                boundInstruments[labelset] = boundInstrument!
+            }
+
+            return boundInstrument!
         }
-        return boundInstrument!
     }
 
     func bind(labels: [String: String]) -> BoundHistogramMetric<T> {

Sources/OpenTelemetrySdk/Metrics/MeterSdk.swift

@@ -195,14 +195,18 @@ class MeterSdk: Meter {
                 let metricName = histogram.key
                 let measureInstrument = histogram.value
                 var metric = Metric(namespace: meterName, name: metricName, desc: meterName + metricName, type: AggregationType.doubleHistogram, resource: resource, instrumentationScopeInfo: instrumentationScopeInfo)
-                measureInstrument.boundInstruments.forEach { boundInstrument in
-                    let labelSet = boundInstrument.key
-                    let aggregator = boundInstrument.value.getAggregator()
-                    aggregator.checkpoint()
-                    var metricData = aggregator.toMetricData()
-                    metricData.labels = labelSet.labels
-                    metric.data.append(metricData)
+
+                measureInstrument.bindUnbindLock.withLock {
+                    measureInstrument.boundInstruments.forEach { boundInstrument in
+                        let labelSet = boundInstrument.key
+                        let aggregator = boundInstrument.value.getAggregator()
+                        aggregator.checkpoint()
+                        var metricData = aggregator.toMetricData()
+                        metricData.labels = labelSet.labels
+                        metric.data.append(metricData)
+                    }
                 }
+
                 metricProcessor.process(metric: metric)
             }