1 files changed, 79 insertions, 0 deletions
diff --git a/browser/base/content/test/performance/PerfTestHelpers.sys.mjs b/browser/base/content/test/performance/PerfTestHelpers.sys.mjs
new file mode 100644
index 0000000000..075e436331
--- /dev/null
+++ b/browser/base/content/test/performance/PerfTestHelpers.sys.mjs
@@ -0,0 +1,79 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const lazy = {};
+
+ChromeUtils.defineModuleGetter(
+  lazy,
+  "NetUtil",
+  "resource://gre/modules/NetUtil.jsm"
+);
+
+export var PerfTestHelpers = {
+  /**
+   * Maps the entries in the given iterable to the given
+   * promise-returning task function, and waits for all returned
+   * promises to have resolved. At most `limit` promises may remain
+   * unresolved at a time. When the limit is reached, the function will
+   * wait for some to resolve before spawning more tasks.
+   */
+  async throttledMapPromises(iterable, task, limit = 64) {
+    let pending = new Set();
+    let promises = [];
+    for (let data of iterable) {
+      while (pending.size >= limit) {
+        await Promise.race(pending);
+      }
+
+      let promise = task(data);
+      promises.push(promise);
+      if (promise) {
+        promise.finally(() => pending.delete(promise));
+        pending.add(promise);
+      }
+    }
+
+    return Promise.all(promises);
+  },
+
+  /**
+   * Returns a promise which resolves to true if the resource at the
+   * given URI exists, false if it doesn't. This should only be used
+   * with local resources, such as from resource:/chrome:/jar:/file:
+   * URIs.
+   */
+  checkURIExists(uri) {
+    return new Promise(resolve => {
+      try {
+        let channel = lazy.NetUtil.newChannel({
+          uri,
+          loadUsingSystemPrincipal: true,
+          // Avoid crashing for non-existant files. If the file not existing
+          // is bad, we can deal with it in the test instead.
+          contentPolicyType: Ci.nsIContentPolicy.TYPE_FETCH,
+        });
+
+        channel.asyncOpen({
+          onStartRequest(request) {
+            resolve(Components.isSuccessCode(request.status));
+            request.cancel(Cr.NS_BINDING_ABORTED);
+          },
+
+          onStopRequest(request, status) {
+            // We should have already resolved from `onStartRequest`, but
+            // we resolve again here just as a failsafe.
+            resolve(Components.isSuccessCode(status));
+          },
+        });
+      } catch (e) {
+        if (
+          e.result != Cr.NS_ERROR_FILE_NOT_FOUND &&
+          e.result != Cr.NS_ERROR_NOT_AVAILABLE
+        ) {
+          throw e;
+        }
+        resolve(false);
+      }
+    });
+  },
+};