Remove AsyncInstrumentRegistry after update to SDK 1.12 (open-telemet…

…ry#5525)

* Remove AsyncInstrumentRegistry after update to SDK 1.12

* added comments

instrumentation/micrometer/micrometer-1.5/library/src/main/java/io/opentelemetry/instrumentation/micrometer/v1_5/DoubleMeasurementRecorder.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.micrometer.v1_5;
+
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.metrics.ObservableDoubleMeasurement;
+import java.lang.ref.WeakReference;
+import java.util.function.Consumer;
+import java.util.function.ToDoubleFunction;
+import javax.annotation.Nullable;
+
+final class DoubleMeasurementRecorder<T> implements Consumer<ObservableDoubleMeasurement> {
+
+  // using a weak reference here so that the existence of the micrometer Meter does not block the
+  // measured object from being GC'd; e.g. a Gauge (or any other async instrument) must not block
+  // garbage collection of the object that it measures
+  private final WeakReference<T> objWeakRef;
+  private final ToDoubleFunction<T> metricFunction;
+  private final Attributes attributes;
+
+  DoubleMeasurementRecorder(
+      @Nullable T obj, ToDoubleFunction<T> metricFunction, Attributes attributes) {
+    this.objWeakRef = new WeakReference<>(obj);
+    this.metricFunction = metricFunction;
+    this.attributes = attributes;
+  }
+
+  @Override
+  public void accept(ObservableDoubleMeasurement measurement) {
+    T obj = objWeakRef.get();
+    if (obj != null) {
+      measurement.record(metricFunction.applyAsDouble(obj), attributes);
+    }
+  }
+}

instrumentation/micrometer/micrometer-1.5/library/src/main/java/io/opentelemetry/instrumentation/micrometer/v1_5/LongMeasurementRecorder.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.micrometer.v1_5;
+
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.metrics.ObservableLongMeasurement;
+import java.lang.ref.WeakReference;
+import java.util.function.Consumer;
+import java.util.function.ToLongFunction;
+import javax.annotation.Nullable;
+
+final class LongMeasurementRecorder<T> implements Consumer<ObservableLongMeasurement> {
+
+  // using a weak reference here so that the existence of the micrometer Meter does not block the
+  // measured object from being GC'd; e.g. a Gauge (or any other async instrument) must not block
+  // garbage collection of the object that it measures
+  private final WeakReference<T> objWeakRef;
+  private final ToLongFunction<T> metricFunction;
+  private final Attributes attributes;
+
+  LongMeasurementRecorder(
+      @Nullable T obj, ToLongFunction<T> metricFunction, Attributes attributes) {
+    this.objWeakRef = new WeakReference<>(obj);
+    this.metricFunction = metricFunction;
+    this.attributes = attributes;
+  }
+
+  @Override
+  public void accept(ObservableLongMeasurement measurement) {
+    T obj = objWeakRef.get();
+    if (obj != null) {
+      measurement.record(metricFunction.applyAsLong(obj), attributes);
+    }
+  }
+}