Opentracing ScopeManager implementation based on our context (#110)

Implementation of ScopeManager based on our own AbstractThreadLocalContext class with the following advantages over the 'standard' opentracing-util ThreadLocalScopeManager:

1. Close is explicitly idempotent; closing more than once has no additional side-effects
(even when finishOnClose is set to true).
2. More predictable behaviour for out-of-order closing of scopes.
Although this is explicitly unsupported by the opentracing specification,
we think having consistent and predictable behaviour is an advantage.
3. Support for {@link nl.talsmasoftware.context.observer.ContextObserver}.
See opentracing/opentracing-java#334 why this is an advantage.

opentracing-span-propagation/src/main/java/nl/talsmasoftware/context/opentracing/ContextScopeManager.java

@@ -0,0 +1,136 @@
+/*
+ * Copyright 2016-2019 Talsma ICT
+ *
+ * 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 nl.talsmasoftware.context.opentracing;
+
+import io.opentracing.Scope;
+import io.opentracing.ScopeManager;
+import io.opentracing.Span;
+import nl.talsmasoftware.context.Context;
+import nl.talsmasoftware.context.ContextManager;
+import nl.talsmasoftware.context.threadlocal.AbstractThreadLocalContext;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/**
+ * Our own implementation of the opentracing {@linkplain ScopeManager}.
+ *
+ * <p>
+ * Manages opentracing {@linkplain Scope} and allows it to be nested within another active scope,
+ * taking care to restore the previous value when closing an active scope.
+ *
+ * <p>
+ * This manager is based on our {@linkplain nl.talsmasoftware.context.threadlocal.AbstractThreadLocalContext}
+ * implementation. Compared to the 'standard' {@linkplain io.opentracing.util.ThreadLocalScopeManager}
+ * this implementation has the following advantages:
+ * <ol>
+ * <li>Close is explicitly idempotent; closing more than once has no additional side-effects
+ * (even when finishOnClose is set to {@code true}).</li>
+ * <li>More predictable behaviour for out-of-order closing of scopes.
+ * Although this is explicitly unsupported by the opentracing specification,
+ * we think having consistent and predictable behaviour is an advantage.
+ * <li>Support for {@link nl.talsmasoftware.context.observer.ContextObserver}.
+ * See https://github.com/opentracing/opentracing-java/issues/334 explicitly wanting this.
+ * </ol>
+ *
+ * <p>
+ * Please note that this scope manager is not somehow automatically enabled.
+ * You will have to provide an instance to your tracer of choice when initializing it.
+ *
+ * <p>
+ * The <em>active span</em> that is automatically propagated when using this
+ * {@code opentracing-span-propagation} library in combination with
+ * the context aware support classes is from the registered ScopeManager
+ * from the {@linkplain io.opentracing.util.GlobalTracer}.
+ *
+ * @since 1.0.6
+ */
+public class ContextScopeManager implements ScopeManager, ContextManager<Span> {
+    /**
+     * Makes the given span the new active span.
+     *
+     * @param span              The span to become the active span.
+     * @param finishSpanOnClose Whether the span should automatically finish when closing the resulting scope.
+     * @return The new active scope (must be closed from the same thread).
+     */
+    @Override
+    public Scope activate(Span span, boolean finishSpanOnClose) {
+        return new ThreadLocalSpanContext(getClass(), span, finishSpanOnClose);
+    }
+
+    /**
+     * The currently active {@link Scope} containing the active span {@link Scope#span()}.
+     *
+     * @return the active scope, or {@code null} if none could be found.
+     */
+    @Override
+    public Scope active() {
+        return ThreadLocalSpanContext.current();
+    }
+
+    /**
+     * Initializes a new context for the given {@linkplain Span}.
+     *
+     * @param value The span to activate.
+     * @return The new active 'Scope'.
+     * @see #activate(Span, boolean)
+     */
+    @Override
+    public Context<Span> initializeNewContext(Span value) {
+        return new ThreadLocalSpanContext(getClass(), value, false);
+    }
+
+    /**
+     * @return The active span context (this is identical to the active scope).
+     * @see #active()
+     */
+    @Override
+    public Context<Span> getActiveContext() {
+        return ThreadLocalSpanContext.current();
+    }
+
+    /**
+     * @return String representation for this context manager.
+     */
+    public String toString() {
+        return getClass().getSimpleName();
+    }
+
+    private static final class ThreadLocalSpanContext extends AbstractThreadLocalContext<Span> implements Scope {
+        private final AtomicBoolean finishOnClose;
+
+        private ThreadLocalSpanContext(Class<? extends ContextManager<? super Span>> contextManagerType, Span newValue, boolean finishOnClose) {
+            super(contextManagerType, newValue);
+            this.finishOnClose = new AtomicBoolean(finishOnClose);
+        }
+
+        private static ThreadLocalSpanContext current() {
+            return current(ThreadLocalSpanContext.class);
+        }
+
+        @Override
+        public Span span() {
+            return value;
+        }
+
+        @Override
+        public void close() {
+            super.close();
+            if (finishOnClose.compareAndSet(true, false) && value != null) {
+                value.finish();
+            }
+        }
+    }
+}

opentracing-span-propagation/src/test/java/nl/talsmasoftware/context/opentracing/ContextScopeManagerObserver.java

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+/*
+ * Copyright 2016-2019 Talsma ICT
+ *
+ * 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 nl.talsmasoftware.context.opentracing;
+
+import io.opentracing.Span;
+import io.opentracing.mock.MockSpan;
+import nl.talsmasoftware.context.ContextManager;
+import nl.talsmasoftware.context.observer.ContextObserver;
+import org.hamcrest.BaseMatcher;
+import org.hamcrest.Description;
+import org.hamcrest.Matcher;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static java.util.Collections.synchronizedList;
+
+public class ContextScopeManagerObserver implements ContextObserver<Span> {
+    static final List<Event> observed = synchronizedList(new ArrayList<Event>());
+
+    @Override
+    public Class<? extends ContextManager<Span>> getObservedContextManager() {
+        return ContextScopeManager.class;
+    }
+
+    @Override
+    public void onActivate(Span activatedContextValue, Span previousContextValue) {
+        observed.add(new Event(Event.Type.ACTIVATE, activatedContextValue));
+    }
+
+    @Override
+    public void onDeactivate(Span deactivatedContextValue, Span restoredContextValue) {
+        observed.add(new Event(Event.Type.DEACTIVATE, deactivatedContextValue));
+    }
+
+    static class Event {
+        enum Type {ACTIVATE, DEACTIVATE}
+
+        final Thread thread;
+        final Type type;
+        final Span value;
+
+        Event(Type type, Span value) {
+            this.thread = Thread.currentThread();
+            this.type = type;
+            this.value = value;
+        }
+
+        @Override
+        public String toString() {
+            return "Event{" + type + ", thread=" + thread.getName() + ", span=" + value + '}';
+        }
+    }
+
+    static class EventMatcher extends BaseMatcher<Event> {
+        Thread inThread;
+        Event.Type type;
+        Matcher<MockSpan> spanMatcher;
+
+        private EventMatcher(Event.Type type, Matcher<MockSpan> spanMatcher) {
+            this.type = type;
+            this.spanMatcher = spanMatcher;
+        }
+
+        static EventMatcher activated(Matcher<MockSpan> span) {
+            return new EventMatcher(Event.Type.ACTIVATE, span);
+        }
+
+        static EventMatcher deactivated(Matcher<MockSpan> span) {
+            return new EventMatcher(Event.Type.DEACTIVATE, span);
+        }
+
+        EventMatcher inThread(Thread thread) {
+            EventMatcher copy = new EventMatcher(type, spanMatcher);
+            copy.inThread = thread;
+            return copy;
+        }
+
+        @Override
+        public boolean matches(Object actual) {
+            if (!(actual instanceof Event)) return actual == null;
+            Event actualEv = (Event) actual;
+            return (inThread == null || inThread.equals(actualEv.thread))
+                    && type.equals(actualEv.type)
+                    && spanMatcher.matches(actualEv.value);
+        }
+
+        @Override
+        public void describeTo(Description description) {
+            description.appendText("Event ");
+            if (inThread != null) description.appendText("in thread ").appendText(inThread.getName());
+            description.appendValue(type).appendText(" ");
+            spanMatcher.describeTo(description);
+        }
+    }
+}