Allow multiple instances of OpenTelemetry primary objects

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

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

@@ -25,6 +25,8 @@
 import io.opentelemetry.trace.DefaultTracer;
 import io.opentelemetry.trace.Tracer;
 import io.opentelemetry.trace.spi.TracerProvider;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
 import java.util.ServiceLoader;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
@@ -33,7 +35,7 @@
  * This class provides a static global accessor for telemetry objects {@link Tracer}, {@link Meter}
  * and {@link DistributedContextManager}.
  *
- * <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
@@ -44,34 +46,40 @@ public final class OpenTelemetry {
 
   @Nullable private static volatile OpenTelemetry instance;
 
-  private final Tracer tracer;
-  private final Meter meter;
-  private final DistributedContextManager contextManager;
+  private final DistributedContextManagerProvider contextManagerProvider;
+  private final TracerProvider tracerProvider;
+  private final MeterProvider meterProvider;
 
   /**
-   * 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 DistributedContextManager}.
+   * Returns an instance of {@link DistributedContextManager}. 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 manager or default via {@link
    *     DefaultDistributedContextManager#getInstance()}.
@@ -80,31 +88,66 @@ public static Meter getMeter() {
    * @since 0.1.0
    */
   public static DistributedContextManager getDistributedContextManager() {
-    return getInstance().contextManager;
+    return getInstance().contextManagerProvider.get();
   }
 
   /**
    * Load provider class via {@link ServiceLoader}. A specific provider class can be requested via
    * setting a system property with FQCN.
    *
    * @param providerClass a provider class
+   * @param classLoader class loader
    * @param <T> provider type
    * @return a provider or null if not found
    * @throws IllegalStateException if a specified provider is not found
    */
   @Nullable
-  private static <T> T loadSpi(Class<T> providerClass) {
+  private static <T> T loadSpiAndCheckSpecified(
+      Class<T> providerClass, final ClassLoader classLoader) {
+    T provider = loadSpi(providerClass, classLoader);
     String specifiedProvider = System.getProperty(providerClass.getName());
-    ServiceLoader<T> providers = ServiceLoader.load(providerClass);
+    if (specifiedProvider != null
+        && !specifiedProvider.equals(provider != null ? provider.getClass().getName() : null)) {
+      throw new IllegalStateException(String.format("Tracer %s not found", specifiedProvider));
+    }
+    return provider;
+  }
+
+  /**
+   * Load provider class via {@link ServiceLoader}.
+   *
+   * @param providerClass a provider class
+   * @param classLoader class loader
+   * @param <T> provider type
+   */
+  @Nullable
+  private static <T> T loadSpi(Class<T> providerClass, final ClassLoader classLoader) {
+    if (classLoader == null) {
+      return null;
+    }
+
+    ClassLoader parentCl =
+        AccessController.doPrivileged(
+            new PrivilegedAction<ClassLoader>() {
+              @Override
+              public ClassLoader run() {
+                return classLoader.getParent();
+              }
+            });
+    // providers packaged in application runtimes have a higher priority
+    // than ones packaged in the application archives
+    T t = loadSpi(providerClass, parentCl);
+    if (t != null) {
+      return t;
+    }
+
+    String specifiedProvider = System.getProperty(providerClass.getName());
+    ServiceLoader<T> providers = ServiceLoader.load(providerClass, classLoader);
     for (T provider : providers) {
       if (specifiedProvider == null || specifiedProvider.equals(provider.getClass().getName())) {
         return provider;
       }
     }
-    if (specifiedProvider != null) {
-      throw new IllegalStateException(
-          String.format("Service provider %s not found", specifiedProvider));
-    }
     return null;
   }
 
@@ -121,16 +164,49 @@ 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();
+    ClassLoader cl =
+        AccessController.doPrivileged(
+            new PrivilegedAction<ClassLoader>() {
+              @Override
+              public ClassLoader run() {
+                return Thread.currentThread().getContextClassLoader();
+              }
+            });
+    if (cl == null) {
+      cl = OpenTelemetry.class.getClassLoader();
+    }
+
+    TracerProvider tracerProvider = loadSpiAndCheckSpecified(TracerProvider.class, cl);
+    this.tracerProvider =
+        tracerProvider != null
+            ? tracerProvider
+            : new TracerProvider() {
+              @Override
+              public Tracer get() {
+                return DefaultTracer.getInstance();
+              }
+            };
+    MeterProvider meterProvider = loadSpiAndCheckSpecified(MeterProvider.class, cl);
+    this.meterProvider =
+        meterProvider != null
+            ? meterProvider
+            : new MeterProvider() {
+              @Override
+              public Meter get() {
+                return DefaultMeter.getInstance();
+              }
+            };
     DistributedContextManagerProvider contextManagerProvider =
-        loadSpi(DistributedContextManagerProvider.class);
-    contextManager =
+        loadSpiAndCheckSpecified(DistributedContextManagerProvider.class, cl);
+    this.contextManagerProvider =
         contextManagerProvider != null
-            ? contextManagerProvider.create()
-            : DefaultDistributedContextManager.getInstance();
+            ? contextManagerProvider
+            : new DistributedContextManagerProvider() {
+              @Override
+              public DistributedContextManager get() {
+                return DefaultDistributedContextManager.getInstance();
+              }
+            };
   }
 
   // for testing

api/src/main/java/io/opentelemetry/distributedcontext/spi/DistributedContextManagerProvider.java

@@ -40,5 +40,5 @@ public interface DistributedContextManagerProvider {
    * @return a {@code DistributedContextManager} instance.
    * @since 0.1.0
    */
-  DistributedContextManager create();
+  DistributedContextManager get();
 }

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

@@ -33,10 +33,11 @@
 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/trace/spi/TracerProvider.java

@@ -33,10 +33,12 @@
 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

@@ -157,6 +157,7 @@ public void testDistributedContextManagerLoadArbitrary() throws IOException {
             FirstDistributedContextManager.class,
             SecondDistributedContextManager.class);
     try {
+      System.out.println(OpenTelemetry.getDistributedContextManager());
       assertTrue(
           (OpenTelemetry.getDistributedContextManager() instanceof FirstDistributedContextManager)
               || (OpenTelemetry.getDistributedContextManager()
@@ -196,7 +197,7 @@ public void testDistributedContextManagerNotFound() {
   }
 
   private static File createService(Class<?> service, Class<?>... impls) throws IOException {
-    URL location = Tracer.class.getProtectionDomain().getCodeSource().getLocation();
+    URL location = OpenTelemetryTest.class.getProtectionDomain().getCodeSource().getLocation();
     File file = new File(location.getPath() + "META-INF/services/" + service.getName());
     file.getParentFile().mkdirs();
 
@@ -211,16 +212,20 @@ 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;
     }
 
     @Nullable
@@ -255,16 +260,20 @@ 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;
     }
 
     @Nullable
@@ -311,17 +320,21 @@ public MeasureBatchRecorder newMeasureBatchRecorder() {
   }
 
   public static class SecondDistributedContextManager extends FirstDistributedContextManager {
+    private static final DistributedContextManager INSTANCE = new SecondDistributedContextManager();
+
     @Override
-    public DistributedContextManager create() {
-      return new SecondDistributedContextManager();
+    public DistributedContextManager get() {
+      return INSTANCE;
     }
   }
 
   public static class FirstDistributedContextManager
       implements DistributedContextManager, DistributedContextManagerProvider {
+    private static final DistributedContextManager INSTANCE = new FirstDistributedContextManager();
+
     @Override
-    public DistributedContextManager create() {
-      return new FirstDistributedContextManager();
+    public DistributedContextManager get() {
+      return INSTANCE;
     }
 
     @Nullable

sdk/src/main/java/io/opentelemetry/sdk/distributedcontext/DistributedContextManagerSdkProvider.java

@@ -27,9 +27,10 @@
  * io.opentelemetry.OpenTelemetry}.
  */
 public class DistributedContextManagerSdkProvider implements DistributedContextManagerProvider {
+  private static final DistributedContextManager INSTANCE = new DistributedContextManagerSdk();
 
   @Override
-  public DistributedContextManager create() {
-    return new DistributedContextManagerSdk();
+  public DistributedContextManager get() {
+    return INSTANCE;
   }
 }

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/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/distributedcontext/DistributedContextManagerSdkProviderTest.java

@@ -27,7 +27,9 @@ public class DistributedContextManagerSdkProviderTest {
 
   @Test
   public void testDefault() {
-    assertThat(new DistributedContextManagerSdkProvider().create())
+    assertThat(new DistributedContextManagerSdkProvider().get())
         .isInstanceOf(DistributedContextManagerSdk.class);
+    assertThat(new DistributedContextManagerSdkProvider().get())
+        .isSameInstanceAs(new DistributedContextManagerSdkProvider().get());
   }
 }

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/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());
   }
 }