5 files changed, 219 insertions, 0 deletions
diff --git a/devtools/shared/commands/object/moz.build b/devtools/shared/commands/object/moz.build
new file mode 100644
index 0000000000..151750907c
--- /dev/null
+++ b/devtools/shared/commands/object/moz.build
@@ -0,0 +1,10 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DevToolsModules(
+    "object-command.js",
+)
+
+if CONFIG["MOZ_BUILD_APP"] != "mobile/android":
+    BROWSER_CHROME_MANIFESTS += ["tests/browser.toml"]
diff --git a/devtools/shared/commands/object/object-command.js b/devtools/shared/commands/object/object-command.js
new file mode 100644
index 0000000000..0396b6167a
--- /dev/null
+++ b/devtools/shared/commands/object/object-command.js
@@ -0,0 +1,63 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+/**
+ * The ObjectCommand helps inspecting and managing lifecycle
+ * of all inspected JavaScript objects.
+ */
+class ObjectCommand {
+  constructor({ commands, descriptorFront, watcherFront }) {
+    this.#commands = commands;
+  }
+  #commands = null;
+
+  /**
+   * Release a set of object actors all at once.
+   *
+   * @param {Array<ObjectFront>} frontsToRelease
+   *        List of fronts for the object to release.
+   */
+  async releaseObjects(frontsToRelease) {
+    // @backward-compat { version 123 } A new Objects Manager front has a new "releaseActors" method.
+    // Only supportsReleaseActors=true codepath can be kept once 123 is the release channel.
+    const { supportsReleaseActors } = this.#commands.client.mainRoot.traits;
+
+    // First group all object fronts per target
+    const actorsPerTarget = new Map();
+    const promises = [];
+    for (const frontToRelease of frontsToRelease) {
+      const { targetFront } = frontToRelease;
+      // If the front is already destroyed, its target front will be nullified.
+      if (!targetFront) {
+        continue;
+      }
+
+      let actorIDsToRemove = actorsPerTarget.get(targetFront);
+      if (!actorIDsToRemove) {
+        actorIDsToRemove = [];
+        actorsPerTarget.set(targetFront, actorIDsToRemove);
+      }
+      if (supportsReleaseActors) {
+        actorIDsToRemove.push(frontToRelease.actorID);
+        frontToRelease.destroy();
+      } else {
+        promises.push(frontToRelease.release());
+      }
+    }
+
+    if (supportsReleaseActors) {
+      // Then release all fronts by bulk per target
+      for (const [targetFront, actorIDs] of actorsPerTarget) {
+        const objectsManagerFront = await targetFront.getFront("objects-manager");
+        promises.push(objectsManagerFront.releaseObjects(actorIDs));
+      }
+    }
+
+    await Promise.all(promises);
+  }
+}
+
+module.exports = ObjectCommand;
diff --git a/devtools/shared/commands/object/tests/browser.toml b/devtools/shared/commands/object/tests/browser.toml
new file mode 100644
index 0000000000..4f1dbe830e
--- /dev/null
+++ b/devtools/shared/commands/object/tests/browser.toml
@@ -0,0 +1,9 @@
+[DEFAULT]
+tags = "devtools"
+subsuite = "devtools"
+support-files = [
+  "!/devtools/client/shared/test/shared-head.js",
+  "head.js",
+]
+
+["browser_object.js"]
diff --git a/devtools/shared/commands/object/tests/browser_object.js b/devtools/shared/commands/object/tests/browser_object.js
new file mode 100644
index 0000000000..9f6d5132d3
--- /dev/null
+++ b/devtools/shared/commands/object/tests/browser_object.js
@@ -0,0 +1,125 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the ObjectCommand
+
+add_task(async function testObjectRelease() {
+  const tab = await addTab("data:text/html;charset=utf-8,Test page<script>var foo = { bar: 42 };</script>");
+
+  const commands = await CommandsFactory.forTab(tab);
+  await commands.targetCommand.startListening();
+
+  const { objectCommand } = commands;
+
+  const evaluationResponse = await commands.scriptCommand.execute(
+    "window.foo"
+  );
+
+  // Execute a second time so that the WebConsoleActor set this._lastConsoleInputEvaluation to another value
+  // and so we prevent freeing `window.foo` 
+  await commands.scriptCommand.execute("");
+
+  await SpecialPowers.spawn(gBrowser.selectedBrowser, [], function () {
+    is(content.wrappedJSObject.foo.bar, 42);
+    const weakRef = Cu.getWeakReference(content.wrappedJSObject.foo);
+
+    // Hold off the weak reference on SpecialPowsers so that it can be accessed in the next SpecialPowers.spawn
+    SpecialPowers.weakRef = weakRef;
+
+    // Nullify this variable so that it should be freed
+    // unless the DevTools inspection still hold it in memory
+    content.wrappedJSObject.foo = null;
+
+    Cu.forceGC();
+    Cu.forceCC();
+
+    ok(SpecialPowers.weakRef.get(), "The 'foo' object can't be freed because of DevTools keeping a reference on it");
+  });
+
+  info("Release the server side actors which are keeping the object in memory");
+  const objectFront = evaluationResponse.result;
+  await commands.objectCommand.releaseObjects([objectFront]);
+
+  ok(objectFront.isDestroyed(), "The passed object front has been destroyed");
+
+  await SpecialPowers.spawn(gBrowser.selectedBrowser, [], async function () {
+    await ContentTaskUtils.waitForCondition(() => {
+      Cu.forceGC();
+      Cu.forceCC();
+      return !SpecialPowers.weakRef.get();
+    }, "Wait for JS object to be freed", 500);
+
+    ok(!SpecialPowers.weakRef.get(), "The 'foo' object has been freed");
+  });
+
+  await commands.destroy();
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testMultiTargetObjectRelease() {
+   // This test fails with EFT disabled
+  if (!isEveryFrameTargetEnabled()) {
+    return;
+  }
+
+  const tab = await addTab(`data:text/html;charset=utf-8,Test page<iframe src="data:text/html,bar">/iframe>`);
+
+  const commands = await CommandsFactory.forTab(tab);
+  await commands.targetCommand.startListening();
+
+  const [,iframeTarget] = commands.targetCommand.getAllTargets(commands.targetCommand.ALL_TYPES);
+  is(iframeTarget.url, "data:text/html,bar");
+
+  const { objectCommand } = commands;
+
+  const evaluationResponse1 = await commands.scriptCommand.execute(
+    "window"
+  );
+  const evaluationResponse2 = await commands.scriptCommand.execute(
+    "window", {
+      selectedTargetFront: iframeTarget,
+    }
+  );
+  const object1 = evaluationResponse1.result;
+  const object2 = evaluationResponse2.result;
+  isnot(object1, object2, "The two window object fronts are different");
+  isnot(object1.targetFront, object2.targetFront, "The two window object fronts relates to two distinct targets");
+  is(object2.targetFront, iframeTarget, "The second object relates to the iframe target");
+
+  await commands.objectCommand.releaseObjects([object1, object2]);
+  ok(object1.isDestroyed(), "The first object front is destroyed");
+  ok(object2.isDestroyed(), "The second object front is destroyed");
+
+  await commands.destroy();
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function testWorkerObjectRelease() {
+  const workerUrl = `data:text/javascript,const foo = {}`;
+  const tab = await addTab(`data:text/html;charset=utf-8,Test page<script>const worker = new Worker("${workerUrl}")</script>`);
+
+  const commands = await CommandsFactory.forTab(tab);
+  commands.targetCommand.listenForWorkers = true;
+  await commands.targetCommand.startListening();
+
+  const [,workerTarget] = commands.targetCommand.getAllTargets(commands.targetCommand.ALL_TYPES);
+  is(workerTarget.url, workerUrl);
+
+  const { objectCommand } = commands;
+
+  const evaluationResponse = await commands.scriptCommand.execute(
+    "foo", {
+      selectedTargetFront: workerTarget,
+    }
+  );
+  const object = evaluationResponse.result;
+  is(object.targetFront, workerTarget, "The 'foo' object relates to the worker target");
+
+  await commands.objectCommand.releaseObjects([object]);
+  ok(object.isDestroyed(), "The object front is destroyed");
+
+  await commands.destroy();
+  BrowserTestUtils.removeTab(tab);
+});
diff --git a/devtools/shared/commands/object/tests/head.js b/devtools/shared/commands/object/tests/head.js
new file mode 100644
index 0000000000..ce65b3d827
--- /dev/null
+++ b/devtools/shared/commands/object/tests/head.js
@@ -0,0 +1,12 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+/* eslint no-unused-vars: [2, {"vars": "local"}] */
+
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/devtools/client/shared/test/shared-head.js",
+  this
+);