1 files changed, 70 insertions, 0 deletions
diff --git a/devtools/shared/commands/resource/tests/browser_resources_target_resources_race.js b/devtools/shared/commands/resource/tests/browser_resources_target_resources_race.js
new file mode 100644
index 0000000000..557d14380a
--- /dev/null
+++ b/devtools/shared/commands/resource/tests/browser_resources_target_resources_race.js
@@ -0,0 +1,70 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Test initial target resources are correctly retrieved even when several calls
+ * to watchResources are made simultaneously.
+ *
+ * This checks a race condition which occurred when calling watchResources
+ * simultaneously. This made the "second" call to watchResources miss existing
+ * resources (in case those are emitted from the target instead of the watcher).
+ * See Bug 1663896.
+ */
+add_task(async function () {
+  // Disable the preloaded process as it creates processes intermittently
+  // which forces the emission of RDP requests we aren't correctly waiting for.
+  await pushPref("dom.ipc.processPrelaunch.enabled", false);
+
+  const { client, resourceCommand, targetCommand } =
+    await initMultiProcessResourceCommand();
+
+  const expectedPlatformMessage = "expectedMessage";
+
+  info("Log a message *before* calling ResourceCommand.watchResources");
+  Services.console.logStringMessage(expectedPlatformMessage);
+
+  info("Call watchResources from 2 separate call sites consecutively");
+
+  // Empty onAvailable callback for CSS MESSAGES, we only want to check that
+  // the second resource we watch correctly provides existing resources.
+  const onCssMessageAvailable = resources => {};
+
+  // First call to watchResources.
+  // We do not await on `watchPromise1` here, in order to simulate simultaneous
+  // calls to watchResources (which could come from 2 separate modules in a real
+  // scenario).
+  const initialWatchPromise = resourceCommand.watchResources(
+    [resourceCommand.TYPES.CSS_MESSAGE],
+    {
+      onAvailable: onCssMessageAvailable,
+    }
+  );
+
+  // `waitForNextResource` will trigger another call to `watchResources`.
+  const { onResource: onMessageReceived } =
+    await resourceCommand.waitForNextResource(
+      resourceCommand.TYPES.PLATFORM_MESSAGE,
+      {
+        ignoreExistingResources: false,
+        predicate: r => r.message === expectedPlatformMessage,
+      }
+    );
+
+  info("Waiting for the expected message to be received");
+  await onMessageReceived;
+  ok(true, "All the expected messages were received");
+
+  info("Wait for the other watchResources promise to finish");
+  await initialWatchPromise;
+
+  // Unwatch all resources.
+  resourceCommand.unwatchResources([resourceCommand.TYPES.CSS_MESSAGE], {
+    onAvailable: onCssMessageAvailable,
+  });
+
+  Services.console.reset();
+  targetCommand.destroy();
+  await client.close();
+});