Allow multiple instances of OpenTelemetry primary objects

Signed-off-by: Pavol Loffay <[email protected]>

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

@@ -32,7 +32,7 @@
  * This class provides a static global accessor for telemetry objects {@link Tracer}, {@link Meter}
  * and {@link Tagger}.
  *
- * <p>The telemetry objects are lazy-loaded singletons resolved via {@link ServiceLoader} mechanism.
+ * <p>The telemetry objects are resolved via {@link ServiceLoader} mechanism.
  *
  * @see TracerProvider
  * @see MeterProvider
@@ -42,41 +42,47 @@ public final class OpenTelemetry {
 
   @Nullable private static volatile OpenTelemetry instance;
 
-  private final Tracer tracer;
-  private final Meter meter;
-  private final Tagger tagger;
+  private final TracerProvider tracerProvider;
+  private final MeterProvider meterProvider;
+  private final TaggerProvider taggerProvider;
 
   /**
-   * Returns a singleton {@link Tracer}.
+   * Returns an instance of {@link Tracer}. In a single deployment runtime a singleton is returned,
+   * however in an application server with multiple deployments a different instance can be used per
+   * deployment.
    *
    * @return registered tracer or default via {@link DefaultTracer#getInstance()}.
    * @throws IllegalStateException if a specified tracer (via system properties) could not be found.
    * @since 0.1.0
    */
   public static Tracer getTracer() {
-    return getInstance().tracer;
+    return getInstance().tracerProvider.get();
   }
 
   /**
-   * Returns a singleton {@link Meter}.
+   * Returns an instance {@link Meter}. In a single deployment runtime a singleton is returned,
+   * however in an application server with multiple deployments a different instance can be used per
+   * deployment.
    *
    * @return registered meter or default via {@link DefaultMeter#getInstance()}.
    * @throws IllegalStateException if a specified meter (via system properties) could not be found.
    * @since 0.1.0
    */
   public static Meter getMeter() {
-    return getInstance().meter;
+    return getInstance().meterProvider.get();
   }
 
   /**
-   * Returns a singleton {@link Tagger}.
+   * Returns an instance of {@link Tagger}. In a single deployment runtime a singleton is returned,
+   * however in an application server with multiple deployments a different instance can be used per
+   * deployment.
    *
    * @return registered meter or default via {@link DefaultTagger#getInstance()}.
    * @throws IllegalStateException if a specified meter (via system properties) could not be found.
    * @since 0.1.0
    */
   public static Tagger getTagger() {
-    return getInstance().tagger;
+    return getInstance().taggerProvider.get();
   }
 
   /**
@@ -89,7 +95,11 @@ public static Tagger getTagger() {
    * @throws IllegalStateException if a specified provider is not found
    */
   @Nullable
-  private static <T> T loadSpi(Class<T> providerClass) {
+  private static <T> T loadSpi(Class<T> providerClass, ClassLoader classLoader) {
+    if (classLoader.getParent() != null) {
+      return loadSpi(providerClass, classLoader.getParent());
+    }
+
     String specifiedProvider = System.getProperty(providerClass.getName());
     ServiceLoader<T> providers = ServiceLoader.load(providerClass);
     for (T provider : providers) {
@@ -116,12 +126,39 @@ private static OpenTelemetry getInstance() {
   }
 
   private OpenTelemetry() {
-    TracerProvider tracerProvider = loadSpi(TracerProvider.class);
-    tracer = tracerProvider != null ? tracerProvider.create() : DefaultTracer.getInstance();
-    MeterProvider meterProvider = loadSpi(MeterProvider.class);
-    meter = meterProvider != null ? meterProvider.create() : DefaultMeter.getInstance();
-    TaggerProvider taggerProvider = loadSpi(TaggerProvider.class);
-    tagger = taggerProvider != null ? taggerProvider.create() : DefaultTagger.getInstance();
+    TracerProvider tracerProvider =
+        loadSpi(TracerProvider.class, Thread.currentThread().getContextClassLoader());
+    this.tracerProvider =
+        tracerProvider != null
+            ? tracerProvider
+            : new TracerProvider() {
+              @Override
+              public Tracer get() {
+                return DefaultTracer.getInstance();
+              }
+            };
+    MeterProvider meterProvider =
+        loadSpi(MeterProvider.class, Thread.currentThread().getContextClassLoader());
+    this.meterProvider =
+        meterProvider != null
+            ? meterProvider
+            : new MeterProvider() {
+              @Override
+              public Meter get() {
+                return DefaultMeter.getInstance();
+              }
+            };
+    TaggerProvider taggerProvider =
+        loadSpi(TaggerProvider.class, Thread.currentThread().getContextClassLoader());
+    this.taggerProvider =
+        taggerProvider != null
+            ? taggerProvider
+            : new TaggerProvider() {
+              @Override
+              public Tagger get() {
+                return DefaultTagger.getInstance();
+              }
+            };
   }
 
   // for testing

api/src/main/java/io/opentelemetry/metrics/spi/MeterProvider.java

@@ -31,10 +31,11 @@
 public interface MeterProvider {
 
   /**
-   * Creates a new meter instance.
+   * Creates a meter instance. In a single deployment runtime a singleton is returned, however in an
+   * application server with multiple deployments a different instance can be used per deployment.
    *
    * @return a meter instance.
    * @since 0.1.0
    */
-  Meter create();
+  Meter get();
 }

api/src/main/java/io/opentelemetry/tags/spi/TaggerProvider.java

@@ -31,10 +31,12 @@
 public interface TaggerProvider {
 
   /**
-   * Creates a new tagger instance.
+   * Creates a tagger instance. In a single deployment runtime a singleton is returned, however in
+   * an application server with multiple deployments a different instance can be used per
+   * deployment.
    *
    * @return a tagger instance.
    * @since 0.1.0
    */
-  Tagger create();
+  Tagger get();
 }

api/src/main/java/io/opentelemetry/trace/spi/TracerProvider.java

@@ -31,10 +31,12 @@
 public interface TracerProvider {
 
   /**
-   * Creates a new tracer instance.
+   * Returns a tracer instance. In a single deployment runtime a singleton is returned, however in
+   * an application server with multiple deployments a different instance can be used per
+   * deployment.
    *
    * @return a tracer instance.
    * @since 0.1.0
    */
-  Tracer create();
+  Tracer get();
 }

api/src/test/java/io/opentelemetry/OpenTelemetryTest.java

@@ -188,16 +188,20 @@ private static File createService(Class<?> service, Class<?>... impls) throws IO
   }
 
   public static class SecondTracer extends FirstTracer {
+    private static final Tracer INSTANCE = new SecondTracer();
+
     @Override
-    public Tracer create() {
-      return new SecondTracer();
+    public Tracer get() {
+      return INSTANCE;
     }
   }
 
   public static class FirstTracer implements Tracer, TracerProvider {
+    private static final Tracer INSTANCE = new FirstTracer();
+
     @Override
-    public Tracer create() {
-      return new FirstTracer();
+    public Tracer get() {
+      return INSTANCE;
     }
 
     @Override
@@ -238,16 +242,20 @@ public HttpTextFormat<SpanContext> getHttpTextFormat() {
   }
 
   public static class SecondMeter extends FirstMeter {
+    private static final Meter INSTANCE = new SecondMeter();
+
     @Override
-    public Meter create() {
-      return new SecondMeter();
+    public Meter get() {
+      return INSTANCE;
     }
   }
 
   public static class FirstMeter implements Meter, MeterProvider {
+    private static final Meter INSTANCE = new FirstMeter();
+
     @Override
-    public Meter create() {
-      return new FirstMeter();
+    public Meter get() {
+      return INSTANCE;
     }
 
     @Override
@@ -286,16 +294,20 @@ public void record(List<Measurement> measurements, TagMap tags, SpanContext span
   }
 
   public static class SecondTagger extends FirstTagger {
+    private static final Tagger INSTANCE = new SecondTagger();
+
     @Override
-    public Tagger create() {
-      return new SecondTagger();
+    public Tagger get() {
+      return INSTANCE;
     }
   }
 
   public static class FirstTagger implements Tagger, TaggerProvider {
+    private static final Tagger INSTANCE = new FirstTagger();
+
     @Override
-    public Tagger create() {
-      return new FirstTagger();
+    public Tagger get() {
+      return INSTANCE;
     }
 
     @Override

sdk/src/main/java/io/opentelemetry/sdk/metrics/MeterSdkProvider.java

@@ -26,9 +26,10 @@
  * io.opentelemetry.OpenTelemetry}.
  */
 public class MeterSdkProvider implements MeterProvider {
+  private static final MeterSdk INSTANCE = new MeterSdk();
 
   @Override
-  public Meter create() {
-    return new MeterSdk();
+  public Meter get() {
+    return INSTANCE;
   }
 }

sdk/src/main/java/io/opentelemetry/sdk/tags/TaggerSdkProvider.java

@@ -26,9 +26,10 @@
  * io.opentelemetry.OpenTelemetry}.
  */
 public class TaggerSdkProvider implements TaggerProvider {
+  private static final TaggerSdk INSTANCE = new TaggerSdk();
 
   @Override
-  public Tagger create() {
-    return new TaggerSdk();
+  public Tagger get() {
+    return INSTANCE;
   }
 }

sdk/src/main/java/io/opentelemetry/sdk/trace/TracerSdkProvider.java

@@ -25,9 +25,10 @@
  * io.opentelemetry.OpenTelemetry}.
  */
 public class TracerSdkProvider implements io.opentelemetry.trace.spi.TracerProvider {
+  private static final TracerSdk INSTANCE = new TracerSdk();
 
   @Override
-  public Tracer create() {
-    return new TracerSdk();
+  public Tracer get() {
+    return INSTANCE;
   }
 }

sdk/src/test/java/io/opentelemetry/sdk/metrics/MeterSdkProviderTest.java

@@ -27,6 +27,7 @@ public class MeterSdkProviderTest {
 
   @Test
   public void testDefault() {
-    assertThat(new MeterSdkProvider().create()).isInstanceOf(MeterSdk.class);
+    assertThat(new MeterSdkProvider().get()).isInstanceOf(MeterSdk.class);
+    assertThat(new MeterSdkProvider().get()).isSameInstanceAs(new MeterSdkProvider().get());
   }
 }

sdk/src/test/java/io/opentelemetry/sdk/tags/TaggerSdkProviderTest.java

@@ -27,6 +27,7 @@ public class TaggerSdkProviderTest {
 
   @Test
   public void testDefault() {
-    assertThat(new TaggerSdkProvider().create()).isInstanceOf(TaggerSdk.class);
+    assertThat(new TaggerSdkProvider().get()).isInstanceOf(TaggerSdk.class);
+    assertThat(new TaggerSdkProvider().get()).isSameInstanceAs(new TaggerSdkProvider().get());
   }
 }

sdk/src/test/java/io/opentelemetry/sdk/trace/TracerSdkProviderTest.java

@@ -27,6 +27,7 @@ public class TracerSdkProviderTest {
 
   @Test
   public void testDefault() {
-    assertThat(new TracerSdkProvider().create()).isInstanceOf(TracerSdk.class);
+    assertThat(new TracerSdkProvider().get()).isInstanceOf(TracerSdk.class);
+    assertThat(new TracerSdkProvider().get()).isSameInstanceAs(new TracerSdkProvider().get());
   }
 }