Make Context.getParentObservation() available for ObservationPredicate (

#3867)

Before these changes, the parent is not available in the context when the ObservationPredicate instances are called, which means decisions cannot be made based on the parent.

Resolves gh-3678

micrometer-observation/src/main/java/io/micrometer/observation/Observation.java

@@ -45,6 +45,7 @@
  * @author Jonatan Ivanov
  * @author Tommy Ludwig
  * @author Marcin Grzejszczak
+ * @author Yanming Zhou
  * @since 1.10.0
  */
 public interface Observation extends ObservationView {
@@ -125,10 +126,11 @@ static <T extends Context> Observation createNotStarted(String name, Supplier<T>
             return NOOP;
         }
         Context context = contextSupplier.get();
+        context.setParentFromCurrentObservation(registry);
         if (!registry.observationConfig().isObservationEnabled(name, context)) {
             return NOOP;
         }
-        return new SimpleObservation(name, registry, context == null ? new Context() : context);
+        return new SimpleObservation(name, registry, context);
     }
 
     // @formatter:off
@@ -168,6 +170,7 @@ static <T extends Context> Observation createNotStarted(@Nullable ObservationCon
         }
         ObservationConvention<T> convention;
         T context = contextSupplier.get();
+        context.setParentFromCurrentObservation(registry);
         if (customConvention != null) {
             convention = customConvention;
         }
@@ -177,7 +180,7 @@ static <T extends Context> Observation createNotStarted(@Nullable ObservationCon
         if (!registry.observationConfig().isObservationEnabled(convention.getName(), context)) {
             return NOOP;
         }
-        return new SimpleObservation(convention, registry, context == null ? new Context() : context);
+        return new SimpleObservation(convention, registry, context);
     }
 
     /**
@@ -311,10 +314,11 @@ static <T extends Context> Observation createNotStarted(ObservationConvention<T>
             return NOOP;
         }
         T context = contextSupplier.get();
+        context.setParentFromCurrentObservation(registry);
         if (!registry.observationConfig().isObservationEnabled(observationConvention.getName(), context)) {
             return NOOP;
         }
-        return new SimpleObservation(observationConvention, registry, context == null ? new Context() : context);
+        return new SimpleObservation(observationConvention, registry, context);
     }
 
     /**
@@ -977,6 +981,20 @@ public void setParentObservation(@Nullable ObservationView parentObservation) {
             this.parentObservation = parentObservation;
         }
 
+        /**
+         * Sets the parent {@link ObservationView} to current one if parent is null and
+         * current one exists.
+         * @param registry the {@link ObservationRegistry} in using
+         */
+        void setParentFromCurrentObservation(ObservationRegistry registry) {
+            if (this.parentObservation == null) {
+                Observation currentObservation = registry.getCurrentObservation();
+                if (currentObservation != null) {
+                    setParentObservation(currentObservation);
+                }
+            }
+        }
+
         /**
          * Error that occurred while processing the {@link Observation}.
          * @return error (null if there wasn't any)

micrometer-observation/src/main/java/io/micrometer/observation/SimpleObservation.java

@@ -35,6 +35,7 @@
  * @author Jonatan Ivanov
  * @author Tommy Ludwig
  * @author Marcin Grzejszczak
+ * @author Yanming Zhou
  * @since 1.10.0
  */
 class SimpleObservation implements Observation {
@@ -61,7 +62,6 @@ class SimpleObservation implements Observation {
         this.convention = getConventionFromConfig(registry, context);
         this.handlers = getHandlersFromConfig(registry, context);
         this.filters = registry.observationConfig().getObservationFilters();
-        setParentFromCurrentObservation();
     }
 
     SimpleObservation(ObservationConvention<? extends Context> convention, ObservationRegistry registry,
@@ -78,14 +78,6 @@ class SimpleObservation implements Observation {
             throw new IllegalStateException(
                     "Convention [" + convention + "] doesn't support context [" + context + "]");
         }
-        setParentFromCurrentObservation();
-    }
-
-    private void setParentFromCurrentObservation() {
-        Observation currentObservation = this.registry.getCurrentObservation();
-        if (currentObservation != null) {
-            this.context.setParentObservation(currentObservation);
-        }
     }
 
     @Nullable

micrometer-observation/src/test/java/io/micrometer/observation/ObservationTests.java

@@ -36,6 +36,7 @@
  * @author Jonatan Ivanov
  * @author Tommy Ludwig
  * @author Marcin Grzejszczak
+ * @author Yanming Zhou
  */
 class ObservationTests {
 
@@ -80,6 +81,20 @@ void matchingPredicateAndHandlerShouldNotResultInNoopObservation() {
         assertThat(observation).isNotSameAs(Observation.NOOP);
     }
 
+    @Test
+    void usingParentObservationToMatchPredicate() {
+        registry.observationConfig().observationHandler(context -> true);
+        registry.observationConfig()
+            .observationPredicate((s, context) -> !s.equals("child") || context.getParentObservation() != null);
+
+        Observation childWithoutParent = Observation.createNotStarted("child", registry);
+        assertThat(childWithoutParent).isSameAs(Observation.NOOP);
+
+        Observation childWithParent = Observation.createNotStarted("parent", registry)
+            .observe(() -> Observation.createNotStarted("child", registry));
+        assertThat(childWithParent).isNotSameAs(Observation.NOOP);
+    }
+
     @Test
     void havingAnObservationFilterWillMutateTheContext() {
         registry.observationConfig().observationHandler(context -> true);