Add Support for Opencensus to OpenTelemetry migration

api/src/main/java/io/opencensus/trace/ContextHandle.java

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2016-17, OpenCensus 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.opencensus.trace;
+
+public interface ContextHandle {
+
+  ContextHandle attach();
+
+  void detach(ContextHandle contextHandle);
+}

api/src/main/java/io/opencensus/trace/ContextManager.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2016-17, OpenCensus 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.opencensus.trace;
+
+public interface ContextManager {
+
+  ContextHandle currentContext();
+
+  ContextHandle withValue(ContextHandle contextHandle, @javax.annotation.Nullable Span span);
+
+  Span getValue(ContextHandle contextHandle);
+}

api/src/main/java/io/opencensus/trace/CurrentSpanUtils.java

@@ -16,14 +16,14 @@
 
 package io.opencensus.trace;
 
-import io.grpc.Context;
 import io.opencensus.common.Scope;
-import io.opencensus.trace.unsafe.ContextUtils;
+import io.opencensus.trace.unsafe.ContextHandleUtils;
 import java.util.concurrent.Callable;
 import javax.annotation.Nullable;
 
 /** Util methods/functionality to interact with the {@link Span} in the {@link io.grpc.Context}. */
 final class CurrentSpanUtils {
+
   // No instance of this class.
   private CurrentSpanUtils() {}
 
@@ -34,7 +34,7 @@ private CurrentSpanUtils() {}
    */
   @Nullable
   static Span getCurrentSpan() {
-    return ContextUtils.getValue(Context.current());
+    return ContextHandleUtils.getValue(ContextHandleUtils.currentContext());
   }
 
   /**
@@ -78,7 +78,8 @@ static <C> Callable<C> withSpan(Span span, boolean endSpan, Callable<C> callable
 
   // Defines an arbitrary scope of code as a traceable operation. Supports try-with-resources idiom.
   private static final class ScopeInSpan implements Scope {
-    private final Context origContext;
+
+    private final ContextHandle origContext;
     private final Span span;
     private final boolean endSpan;
 
@@ -90,19 +91,21 @@ private static final class ScopeInSpan implements Scope {
     private ScopeInSpan(Span span, boolean endSpan) {
       this.span = span;
       this.endSpan = endSpan;
-      origContext = ContextUtils.withValue(Context.current(), span).attach();
+      origContext =
+          ContextHandleUtils.withValue(ContextHandleUtils.currentContext(), span).attach();
     }
 
     @Override
     public void close() {
-      Context.current().detach(origContext);
+      ContextHandleUtils.currentContext().detach(origContext);
       if (endSpan) {
         span.end();
       }
     }
   }
 
   private static final class RunnableInSpan implements Runnable {
+
     // TODO(bdrutu): Investigate if the extra private visibility increases the generated bytecode.
     private final Span span;
     private final Runnable runnable;
@@ -116,7 +119,8 @@ private RunnableInSpan(Span span, Runnable runnable, boolean endSpan) {
 
     @Override
     public void run() {
-      Context origContext = ContextUtils.withValue(Context.current(), span).attach();
+      ContextHandle origContext =
+          ContextHandleUtils.withValue(ContextHandleUtils.currentContext(), span).attach();
       try {
         runnable.run();
       } catch (Throwable t) {
@@ -128,7 +132,7 @@ public void run() {
         }
         throw new RuntimeException("unexpected", t);
       } finally {
-        Context.current().detach(origContext);
+        ContextHandleUtils.currentContext().detach(origContext);
         if (endSpan) {
           span.end();
         }
@@ -137,6 +141,7 @@ public void run() {
   }
 
   private static final class CallableInSpan<V> implements Callable<V> {
+
     private final Span span;
     private final Callable<V> callable;
     private final boolean endSpan;
@@ -149,7 +154,8 @@ private CallableInSpan(Span span, Callable<V> callable, boolean endSpan) {
 
     @Override
     public V call() throws Exception {
-      Context origContext = ContextUtils.withValue(Context.current(), span).attach();
+      ContextHandle origContext =
+          ContextHandleUtils.withValue(ContextHandleUtils.currentContext(), span).attach();
       try {
         return callable.call();
       } catch (Exception e) {
@@ -162,7 +168,7 @@ public V call() throws Exception {
         }
         throw new RuntimeException("unexpected", t);
       } finally {
-        Context.current().detach(origContext);
+        ContextHandleUtils.currentContext().detach(origContext);
         if (endSpan) {
           span.end();
         }

api/src/main/java/io/opencensus/trace/Tracing.java

@@ -32,6 +32,7 @@
  * @since 0.5
  */
 public final class Tracing {
+
   private static final Logger logger = Logger.getLogger(Tracing.class.getName());
   private static final TraceComponent traceComponent =
       loadTraceComponent(TraceComponent.class.getClassLoader());
@@ -89,6 +90,21 @@ public static TraceConfig getTraceConfig() {
   // Any provider that may be used for TraceComponent can be added here.
   @DefaultVisibilityForTesting
   static TraceComponent loadTraceComponent(@Nullable ClassLoader classLoader) {
+    try {
+      // Call Class.forName with literal string name of the class to help shading tools.
+      return Provider.createInstance(
+          Class.forName(
+              "io.opentelemetry.opencensusshim.OpenTelemetryTraceComponentImpl",
+              /*initialize=*/ true,
+              classLoader),
+          TraceComponent.class);
+    } catch (ClassNotFoundException e) {
+      logger.log(
+          Level.FINE,
+          "Couldn't load full implementation for OpenTelemetry TraceComponent, now trying to load "
+              + "original implementation.",
+          e);
+    }
     try {
       // Call Class.forName with literal string name of the class to help shading tools.
       return Provider.createInstance(

api/src/main/java/io/opencensus/trace/unsafe/ContextHandleImpl.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2016-17, OpenCensus 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.opencensus.trace.unsafe;
+
+import io.grpc.Context;
+import io.opencensus.trace.ContextHandle;
+
+/** {@code ContextHandle} implementation using {@see io.grpc.Context}. */
+class ContextHandleImpl implements ContextHandle {
+
+  private final Context context;
+
+  public ContextHandleImpl(Context context) {
+    this.context = context;
+  }
+
+  Context getContext() {
+    return context;
+  }
+
+  @Override
+  public ContextHandle attach() {
+    return new ContextHandleImpl(context.attach());
+  }
+
+  @Override
+  public void detach(ContextHandle contextHandle) {
+    ContextHandleImpl impl = (ContextHandleImpl) contextHandle;
+    context.detach(impl.context);
+  }
+}

api/src/main/java/io/opencensus/trace/unsafe/ContextHandleUtils.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright 2016-17, OpenCensus 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.opencensus.trace.unsafe;
+
+import io.opencensus.internal.Provider;
+import io.opencensus.trace.ContextHandle;
+import io.opencensus.trace.ContextManager;
+import io.opencensus.trace.Span;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import javax.annotation.Nullable;
+
+public class ContextHandleUtils {
+
+  // No instance of this class.
+  private ContextHandleUtils() {}
+
+  private static final Logger LOGGER = Logger.getLogger(ContextHandleUtils.class.getName());
+  private static final ContextManager CONTEXT_MANAGER =
+      loadContextManager(ContextManager.class.getClassLoader());
+
+  private static ContextManager loadContextManager(@Nullable ClassLoader classLoader) {
+    try {
+      return Provider.createInstance(
+          Class.forName(
+              "io.opentelemetry.opencensusshim.OpenTelemetryContextManager",
+              /*initialize=*/ true,
+              classLoader),
+          ContextManager.class);
+    } catch (ClassNotFoundException e) {
+      LOGGER.log(
+          Level.FINE,
+          "Couldn't load full implementation for OpenTelemetry context manager, now loading "
+              + "original implementation.",
+          e);
+    }
+    return new ContextManagerImpl();
+  }
+
+  public static ContextHandle currentContext() {
+    return CONTEXT_MANAGER.currentContext();
+  }
+
+  /**
+   * Creates a new {@code ContextHandle} with the given value set.
+   *
+   * @param context the parent {@code ContextHandle}.
+   * @param span the value to be set.
+   * @return a new context with the given value set.
+   */
+  public static ContextHandle withValue(
+      ContextHandle context, @javax.annotation.Nullable Span span) {
+    return CONTEXT_MANAGER.withValue(context, span);
+  }
+
+  /**
+   * Returns the value from the specified {@code ContextHandle}.
+   *
+   * @param context the specified {@code ContextHandle}.
+   * @return the value from the specified {@code ContextHandle}.
+   */
+  public static Span getValue(ContextHandle context) {
+    return CONTEXT_MANAGER.getValue(context);
+  }
+}

api/src/main/java/io/opencensus/trace/unsafe/ContextManagerImpl.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2016-17, OpenCensus 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.opencensus.trace.unsafe;
+
+import io.grpc.Context;
+import io.opencensus.trace.ContextHandle;
+import io.opencensus.trace.ContextManager;
+import io.opencensus.trace.Span;
+import javax.annotation.Nullable;
+
+/** Default {@code ContextManager} implementation using io.grpc.Context */
+public class ContextManagerImpl implements ContextManager {
+
+  @Override
+  public ContextHandle currentContext() {
+    return wrapContext(Context.current());
+  }
+
+  @Override
+  public ContextHandle withValue(ContextHandle contextHandle, @Nullable Span span) {
+    return wrapContext(ContextUtils.withValue(unwrapContext(contextHandle), span));
+  }
+
+  @Override
+  public Span getValue(ContextHandle contextHandle) {
+    return ContextUtils.getValue(unwrapContext(contextHandle));
+  }
+
+  private static ContextHandle wrapContext(Context context) {
+    return new ContextHandleImpl(context);
+  }
+
+  private static Context unwrapContext(ContextHandle contextHandle) {
+    return ((ContextHandleImpl) contextHandle).getContext();
+  }
+
+  protected ContextManagerImpl() {}
+}

api/src/main/java/io/opencensus/trace/unsafe/ContextUtils.java

@@ -33,7 +33,7 @@
  *
  * @since 0.5
  */
-public final class ContextUtils {
+final class ContextUtils {
   // No instance of this class.
   private ContextUtils() {}