Fix continuation metrics (#8635)

Move capture and canceled continuation metrics to the same class (previously we only recorded a canceled continuation metric when pending trace was enabled, not when streaming spans)

Fixed finished continuation metric (this was in the wrong place which meant it was only recorded when closing message spans)

Author: mcculls

dd-trace-core/src/main/java/datadog/trace/core/PendingTrace.java

@@ -264,9 +264,8 @@ public void registerContinuation(final AgentScope.Continuation continuation) {
   }
 
   @Override
-  public void cancelContinuation(final AgentScope.Continuation continuation) {
+  public void removeContinuation(final AgentScope.Continuation continuation) {
     decrementRefAndMaybeWrite(false);
-    healthMetrics.onCancelContinuation();
   }
 
   private PublishState decrementRefAndMaybeWrite(boolean isRootSpan) {

dd-trace-core/src/main/java/datadog/trace/core/StreamingTraceCollector.java

@@ -82,7 +82,7 @@ public void registerContinuation(AgentScope.Continuation continuation) {
   }
 
   @Override
-  public void cancelContinuation(AgentScope.Continuation continuation) {
+  public void removeContinuation(AgentScope.Continuation continuation) {
     // do nothing
   }
 }

dd-trace-core/src/main/java/datadog/trace/core/scopemanager/ContinuableScopeManager.java

@@ -107,10 +107,7 @@ public AgentScope.Continuation captureSpan(final AgentSpan span) {
   }
 
   private AgentScope.Continuation captureSpan(final AgentSpan span, byte source) {
-    ScopeContinuation continuation = new ScopeContinuation(this, span, source);
-    continuation.register();
-    healthMetrics.onCaptureContinuation();
-    return continuation;
+    return new ScopeContinuation(this, span, source).register();
   }
 
   private AgentScope activate(
@@ -207,7 +204,6 @@ public void closePrevious(final boolean finishSpan) {
       scopeStack.cleanup();
       if (finishSpan) {
         top.span.finishWithEndToEnd();
-        healthMetrics.onFinishContinuation();
       }
     }
   }

dd-trace-core/src/main/java/datadog/trace/core/scopemanager/ScopeContinuation.java

@@ -62,6 +62,7 @@ final class ScopeContinuation implements AgentScope.Continuation {
 
   ScopeContinuation register() {
     traceCollector.registerContinuation(this);
+    scopeManager.healthMetrics.onCaptureContinuation();
     return this;
   }
 
@@ -95,17 +96,20 @@ public void cancel() {
     while (current == 0) {
       // no outstanding activations and hold has been removed
       if (COUNT.compareAndSet(this, current, CANCELLED)) {
-        traceCollector.cancelContinuation(this);
+        traceCollector.removeContinuation(this);
+        scopeManager.healthMetrics.onFinishContinuation();
         return;
       }
       current = count;
     }
+    scopeManager.healthMetrics.onCancelContinuation();
   }
 
   void cancelFromContinuedScopeClose() {
     if (COUNT.compareAndSet(this, 1, CANCELLED)) {
       // fast path: only one activation of the continuation (no hold)
-      traceCollector.cancelContinuation(this);
+      traceCollector.removeContinuation(this);
+      scopeManager.healthMetrics.onFinishContinuation();
     } else if (COUNT.decrementAndGet(this) == 0) {
       // slow path: multiple activations, all have now closed (no hold)
       cancel();

dd-trace-core/src/test/groovy/datadog/trace/core/PendingTraceStrictWriteTest.groovy

@@ -56,8 +56,8 @@ class PendingTraceStrictWriteTest extends PendingTraceTestBase {
 
     when: "continuation is finished the second time"
     // Yes this should be guarded by the used flag in the continuation,
-    // so cancel it anyway to trigger the exception
-    traceCollector.cancelContinuation(continuation)
+    // so remove it anyway to trigger the exception
+    traceCollector.removeContinuation(continuation)
 
     then:
     thrown IllegalStateException

internal-api/src/main/java/datadog/trace/bootstrap/instrumentation/api/AgentTraceCollector.java

@@ -3,5 +3,5 @@
 public interface AgentTraceCollector {
   void registerContinuation(AgentScope.Continuation continuation);
 
-  void cancelContinuation(AgentScope.Continuation continuation);
+  void removeContinuation(AgentScope.Continuation continuation);
 }

internal-api/src/main/java/datadog/trace/bootstrap/instrumentation/api/AgentTracer.java

@@ -679,7 +679,7 @@ public static class NoopAgentTraceCollector implements AgentTraceCollector {
     public void registerContinuation(final AgentScope.Continuation continuation) {}
 
     @Override
-    public void cancelContinuation(final AgentScope.Continuation continuation) {}
+    public void removeContinuation(final AgentScope.Continuation continuation) {}
   }
 
   public static class NoopAgentHistogram implements AgentHistogram {