Add named meter and meter factory (#668)

* Add named meters with factory provider

* Fix documentation to instantiate a meter from a meter factory

* Fix documentation incorrectly referencing meter not meter factory

* Fix MeterFactor not Meter

Co-Authored-By: Armin Ruech <[email protected]>

* Fix MeterFactor not Meter

Co-Authored-By: Armin Ruech <[email protected]>

* Fix MeterFactory not Meter

Co-Authored-By: Armin Ruech <[email protected]>

* Fix over 100 characters in line

* Refactor meter example names to my_library_example

Author: ptravers

api/src/main/java/io/opentelemetry/OpenTelemetry.java

@@ -19,9 +19,11 @@
 import io.opentelemetry.distributedcontext.DefaultDistributedContextManager;
 import io.opentelemetry.distributedcontext.DistributedContextManager;
 import io.opentelemetry.distributedcontext.spi.DistributedContextManagerProvider;
-import io.opentelemetry.metrics.DefaultMeter;
+import io.opentelemetry.metrics.DefaultMeterFactory;
+import io.opentelemetry.metrics.DefaultMeterFactoryProvider;
 import io.opentelemetry.metrics.Meter;
-import io.opentelemetry.metrics.spi.MeterProvider;
+import io.opentelemetry.metrics.MeterFactory;
+import io.opentelemetry.metrics.spi.MeterFactoryProvider;
 import io.opentelemetry.trace.DefaultTracerFactory;
 import io.opentelemetry.trace.DefaultTracerFactoryProvider;
 import io.opentelemetry.trace.Tracer;
@@ -38,7 +40,7 @@
  * <p>The telemetry objects are lazy-loaded singletons resolved via {@link ServiceLoader} mechanism.
  *
  * @see TracerFactory
- * @see MeterProvider
+ * @see MeterFactoryProvider
  * @see DistributedContextManagerProvider
  */
 @ThreadSafe
@@ -47,7 +49,7 @@ public final class OpenTelemetry {
   @Nullable private static volatile OpenTelemetry instance;
 
   private final TracerFactory tracerFactory;
-  private final Meter meter;
+  private final MeterFactory meterFactory;
   private final DistributedContextManager contextManager;
 
   /**
@@ -63,14 +65,15 @@ public static TracerFactory getTracerFactory() {
   }
 
   /**
-   * Returns a singleton {@link Meter}.
+   * Returns a singleton {@link MeterFactory}.
    *
-   * @return registered meter or default via {@link DefaultMeter#getInstance()}.
-   * @throws IllegalStateException if a specified meter (via system properties) could not be found.
+   * @return registered MeterFactory or default via {@link DefaultMeterFactory#getInstance()}.
+   * @throws IllegalStateException if a specified MeterFactory (via system properties) could not be
+   *     found.
    * @since 0.1.0
    */
-  public static Meter getMeter() {
-    return getInstance().meter;
+  public static MeterFactory getMeterFactory() {
+    return getInstance().meterFactory;
   }
 
   /**
@@ -105,8 +108,11 @@ private OpenTelemetry() {
             ? tracerFactoryProvider.create()
             : DefaultTracerFactoryProvider.getInstance().create();
 
-    MeterProvider meterProvider = loadSpi(MeterProvider.class);
-    meter = meterProvider != null ? meterProvider.create() : DefaultMeter.getInstance();
+    MeterFactoryProvider meterFactoryProvider = loadSpi(MeterFactoryProvider.class);
+    meterFactory =
+        meterFactoryProvider != null
+            ? meterFactoryProvider.create()
+            : DefaultMeterFactoryProvider.getInstance().create();
     DistributedContextManagerProvider contextManagerProvider =
         loadSpi(DistributedContextManagerProvider.class);
     contextManager =

api/src/main/java/io/opentelemetry/metrics/CounterDouble.java

@@ -29,7 +29,7 @@
  * <pre>{@code
  * class YourClass {
  *
- *   private static final Meter meter = OpenTelemetry.getMeter();
+ *   private static final Meter meter = OpenTelemetry.getMeterFactory().get("my_library_name");
  *   private static final CounterDouble counter =
  *       meter.
  *           .counterDoubleBuilder("processed_jobs")

api/src/main/java/io/opentelemetry/metrics/CounterLong.java

@@ -29,7 +29,7 @@
  * <pre>{@code
  * class YourClass {
  *
- *   private static final Meter meter = OpenTelemetry.getMeter();
+ *   private static final Meter meter = OpenTelemetry.getMeterFactory().get("my_library_name");
  *   private static final CounterLong counter =
  *       meter.
  *           .counterLongBuilder("processed_jobs")

api/src/main/java/io/opentelemetry/metrics/DefaultMeterFactory.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2019, OpenTelemetry 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.
+ */
+
+package io.opentelemetry.metrics;
+
+public class DefaultMeterFactory implements MeterFactory {
+
+  private static final MeterFactory instance = new DefaultMeterFactory();
+
+  public static MeterFactory getInstance() {
+    return instance;
+  }
+
+  @Override
+  public Meter get(String instrumentationName) {
+    return get(instrumentationName, null);
+  }
+
+  @Override
+  public Meter get(String instrumentationName, String instrumentationVersion) {
+    return DefaultMeter.getInstance();
+  }
+}

api/src/main/java/io/opentelemetry/metrics/DefaultMeterFactoryProvider.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2019, OpenTelemetry 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.
+ */
+
+package io.opentelemetry.metrics;
+
+import io.opentelemetry.metrics.spi.MeterFactoryProvider;
+
+public class DefaultMeterFactoryProvider implements MeterFactoryProvider {
+  private static final MeterFactoryProvider instance = new DefaultMeterFactoryProvider();
+
+  public static MeterFactoryProvider getInstance() {
+    return instance;
+  }
+
+  @Override
+  public MeterFactory create() {
+    return DefaultMeterFactory.getInstance();
+  }
+}

api/src/main/java/io/opentelemetry/metrics/GaugeDouble.java

@@ -29,7 +29,7 @@
  * <pre>{@code
  * class YourClass {
  *
- *   private static final Meter meter = OpenTelemetry.getMeter();
+ *   private static final Meter meter = OpenTelemetry.getMeterFactory().get("my_library_name");
  *   private static final GaugeDouble gauge =
  *       meter
  *           .gaugeDoubleBuilder("processed_jobs")

api/src/main/java/io/opentelemetry/metrics/GaugeLong.java

@@ -29,7 +29,7 @@
  * <pre>{@code
  * class YourClass {
  *
- *   private static final Meter meter = OpenTelemetry.getMeter();
+ *   private static final Meter meter = OpenTelemetry.getMeterFactory().get("my_library_name");
  *   private static final GaugeLong gauge =
  *       meter
  *           .gaugeLongBuilder("processed_jobs")

api/src/main/java/io/opentelemetry/metrics/MeasureDouble.java

@@ -26,7 +26,7 @@
  * <pre>{@code
  * class YourClass {
  *
- *   private static final Meter meter = OpenTelemetry.getMeter();
+ *   private static final Meter meter = OpenTelemetry.getMeterFactory().get("my_library_name");
  *   private static final MeasureDouble measure =
  *       meter.
  *           .measureDoubleBuilder("doWork_latency")

api/src/main/java/io/opentelemetry/metrics/MeasureLong.java

@@ -26,7 +26,7 @@
  * <pre>{@code
  * class YourClass {
  *
- *   private static final Meter meter = OpenTelemetry.getMeter();
+ *   private static final Meter meter = OpenTelemetry.getMeterFactory().get("my_library_name");
  *   private static final MeasureLong measure =
  *       meter.
  *           .measureLongBuilder("doWork_latency")

api/src/main/java/io/opentelemetry/metrics/Meter.java

@@ -35,7 +35,7 @@
  *
  * <pre>{@code
  * class MyClass {
- *   private static final Meter meter = Metrics.getMeter();
+ *   private static final Meter meter = Metrics.getMeterFactory().get("my_library_name");
  *   private static final MeasureDouble cacheHit = meter.measureDoubleBuilder("cache_hit").build();
  *
  *   Response serverHandler(Request request) {
@@ -53,7 +53,7 @@
  *
  * <pre>{@code
  * class YourClass {
- *   private static final Meter meter = Metrics.getMeter();
+ *   private static final Meter meter = Metrics.getMeterFactory().get("my_library_name");
  *   private static final CounterLong collectionMetric =
  *       meter
  *           .counterLongBuilder("collection")
@@ -83,7 +83,7 @@
  *
  * <pre>{@code
  * class YourClass {
- *   private static final Meter meter = Metrics.getMeter();
+ *   private static final Meter meter = Metrics.getMeterFactory().get("my_library_name");
  *   private static final List<String> keys = Collections.singletonList("Name");
  *   private static final List<String> values = Collections.singletonList("Inbound");
  *   private static final GaugeDouble gauge =