Bug 1923903 - [devtools] Instantiate only one object actor per JS object in the JS Tracer. r=devtools-reviewers,bomsy

This will allow to compare Object Actor's IDs in order to track any JS Object
recorded in the trace.

Differential Revision: https://phabricator.services.mozilla.com/D223782

devtools/server/actors/tracer.js

@@ -14,6 +14,10 @@ ChromeUtils.defineESModuleGetters(
 );
 
 const { Actor } = require("resource://devtools/shared/protocol.js");
+const { createValueGrip } = require("devtools/server/actors/object/utils");
+const {
+  ObjectActorPool,
+} = require("resource://devtools/server/actors/object/ObjectActorPool.js");
 const {
   tracerSpec,
   TRACER_LOG_METHODS,
@@ -82,6 +86,14 @@ class TracerActor extends Actor {
   // This is used by the profiler log method and the getProfile method.
   #stopResult = null;
 
+  // A Pool for all JS values emitted by the Tracer Actor.
+  // This helps instantiate a unique Object Actor per JS Object communicated to the client.
+  // This also helps share the same Object Actor instances when evaluating JS via
+  // the console actor.
+  // This pool is created lazily, only once we start a new trace.
+  // We also clear the pool before starting the trace.
+  #tracerPool = null;
+
   destroy() {
     this.stopTracing();
   }
@@ -152,6 +164,14 @@ class TracerActor extends Actor {
       return;
     }
 
+    // Flush any previous recorded data only when we start a new tracer
+    // as we may still analyse trace data after stopping the trace.
+    // The pool will then be re-created on demand from createValueGrip.
+    if (this.#tracerPool) {
+      this.#tracerPool.destroy();
+      this.#tracerPool = null;
+    }
+
     this.logMethod = options.logMethod || TRACER_LOG_METHODS.STDOUT;
 
     let ListenerClass = null;
@@ -240,5 +260,17 @@ class TracerActor extends Actor {
     }
     return null;
   }
+
+  createValueGrip(value) {
+    if (!this.#tracerPool) {
+      this.#tracerPool = new ObjectActorPool(
+        this.targetActor.threadActor,
+        "tracer",
+        true
+      );
+      this.manage(this.#tracerPool);
+    }
+    return createValueGrip(this, value, this.#tracerPool);
+  }
 }
 exports.TracerActor = TracerActor;

devtools/server/actors/tracer/resources.js

@@ -6,10 +6,7 @@
 
 const { throttle } = require("resource://devtools/shared/throttle.js");
 
-const {
+const { makeDebuggeeValue } = require("devtools/server/actors/object/utils");
-  makeDebuggeeValue,
-  createValueGripForTarget,
-} = require("devtools/server/actors/object/utils");
 
 const {
   TYPES,
@@ -163,7 +160,7 @@ class ResourcesTracingListener {
       ChromeUtils.dateNow(),
       depth,
       type,
-      createValueGripForTarget(this.targetActor, dbgObj),
+      this.traceActor.createValueGrip(dbgObj),
     ]);
     this.throttleEmitTraces();
     return false;
@@ -324,7 +321,7 @@ class ResourcesTracingListener {
         }
         // Instantiate a object actor so that the tools can easily inspect these objects
         const dbgObj = makeDebuggeeValue(this.targetActor, arg);
-        args.push(createValueGripForTarget(this.targetActor, dbgObj));
+        args.push(this.traceActor.createValueGrip(dbgObj));
       }
       argNames = frame.callee.script.parameterNames;
     }
@@ -415,7 +412,7 @@ class ResourcesTracingListener {
       }
       // Instantiate a object actor so that the tools can easily inspect these objects
       const dbgObj = makeDebuggeeValue(this.targetActor, rv);
-      returnedValue = createValueGripForTarget(this.targetActor, dbgObj);
+      returnedValue = this.traceActor.createValueGrip(dbgObj);
     }
 
     const frameIndex = this.#getFrameIndex(