1 files changed, 234 insertions, 0 deletions
diff --git a/browser/components/sessionstore/TabStateFlusher.sys.mjs b/browser/components/sessionstore/TabStateFlusher.sys.mjs
new file mode 100644
index 0000000000..897d02b6f6
--- /dev/null
+++ b/browser/components/sessionstore/TabStateFlusher.sys.mjs
@@ -0,0 +1,234 @@
+/* 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/. */
+
+const lazy = {};
+ChromeUtils.defineESModuleGetters(lazy, {
+  SessionStore: "resource:///modules/sessionstore/SessionStore.sys.mjs",
+});
+
+/**
+ * A module that enables async flushes. Updates from frame scripts are
+ * throttled to be sent only once per second. If an action wants a tab's latest
+ * state without waiting for a second then it can request an async flush and
+ * wait until the frame scripts reported back. At this point the parent has the
+ * latest data and the action can continue.
+ */
+export var TabStateFlusher = Object.freeze({
+  /**
+   * Requests an async flush for the given browser. Returns a promise that will
+   * resolve when we heard back from the content process and the parent has
+   * all the latest data.
+   */
+  flush(browser) {
+    return TabStateFlusherInternal.flush(browser);
+  },
+
+  /**
+   * Requests an async flush for all browsers of a given window. Returns a Promise
+   * that will resolve when we've heard back from all browsers.
+   */
+  flushWindow(window) {
+    return TabStateFlusherInternal.flushWindow(window);
+  },
+
+  /**
+   * Resolves the flush request with the given flush ID.
+   *
+   * @param browser (<xul:browser>)
+   *        The browser for which the flush is being resolved.
+   * @param flushID (int)
+   *        The ID of the flush that was sent to the browser.
+   * @param success (bool, optional)
+   *        Whether or not the flush succeeded.
+   * @param message (string, optional)
+   *        An error message that will be sent to the Console in the
+   *        event that a flush failed.
+   */
+  resolve(browser, flushID, success = true, message = "") {
+    TabStateFlusherInternal.resolve(browser, flushID, success, message);
+  },
+
+  /**
+   * Resolves all active flush requests for a given browser. This should be
+   * used when the content process crashed or the final update message was
+   * seen. In those cases we can't guarantee to ever hear back from the frame
+   * script so we just resolve all requests instead of discarding them.
+   *
+   * @param browser (<xul:browser>)
+   *        The browser for which all flushes are being resolved.
+   * @param success (bool, optional)
+   *        Whether or not the flushes succeeded.
+   * @param message (string, optional)
+   *        An error message that will be sent to the Console in the
+   *        event that the flushes failed.
+   */
+  resolveAll(browser, success = true, message = "") {
+    TabStateFlusherInternal.resolveAll(browser, success, message);
+  },
+});
+
+var TabStateFlusherInternal = {
+  // Stores the last request ID.
+  _lastRequestID: 0,
+
+  // A map storing all active requests per browser. A request is a
+  // triple of a map containing all flush requests, a promise that
+  // resolve when a request for a browser is canceled, and the
+  // function to call to cancel a reqeust.
+  _requests: new WeakMap(),
+
+  initEntry(entry) {
+    entry.perBrowserRequests = new Map();
+    entry.cancelPromise = new Promise(resolve => {
+      entry.cancel = resolve;
+    }).then(result => {
+      TabStateFlusherInternal.initEntry(entry);
+      return result;
+    });
+
+    return entry;
+  },
+
+  /**
+   * Requests an async flush for the given browser. Returns a promise that will
+   * resolve when we heard back from the content process and the parent has
+   * all the latest data.
+   */
+  flush(browser) {
+    let id = ++this._lastRequestID;
+    let nativePromise = Promise.resolve();
+    if (browser && browser.frameLoader) {
+      /*
+        Request native listener to flush the tabState.
+        Resolves when flush is complete.
+      */
+      nativePromise = browser.frameLoader.requestTabStateFlush();
+    }
+
+    if (!Services.appinfo.sessionHistoryInParent) {
+      /*
+        In the event that we have to trigger a process switch and thus change
+        browser remoteness, session store needs to register and track the new
+        browser window loaded and to have message manager listener registered
+        ** before ** TabStateFlusher send "SessionStore:flush" message. This fixes
+        the race where we send the message before the message listener is
+        registered for it.
+        */
+      lazy.SessionStore.ensureInitialized(browser.ownerGlobal);
+
+      let mm = browser.messageManager;
+      mm.sendAsyncMessage("SessionStore:flush", {
+        id,
+        epoch: lazy.SessionStore.getCurrentEpoch(browser),
+      });
+    }
+
+    // Retrieve active requests for given browser.
+    let permanentKey = browser.permanentKey;
+    let request = this._requests.get(permanentKey);
+    if (!request) {
+      // If we don't have any requests for this browser, create a new
+      // entry for browser.
+      request = this.initEntry({});
+      this._requests.set(permanentKey, request);
+    }
+
+    // Non-SHIP flushes resolve this after the "SessionStore:update" message. We
+    // don't use that message for SHIP, so it's fine to resolve the request
+    // immediately after the native promise resolves, since SessionStore will
+    // have processed all updates from this browser by that point.
+    let requestPromise = Promise.resolve();
+    if (!Services.appinfo.sessionHistoryInParent) {
+      requestPromise = new Promise(resolve => {
+        // Store resolve() so that we can resolve the promise later.
+        request.perBrowserRequests.set(id, resolve);
+      });
+    }
+
+    return Promise.race([
+      nativePromise.then(_ => requestPromise),
+      request.cancelPromise,
+    ]);
+  },
+
+  /**
+   * Requests an async flush for all non-lazy browsers of a given window.
+   * Returns a Promise that will resolve when we've heard back from all browsers.
+   */
+  flushWindow(window) {
+    let promises = [];
+    for (let browser of window.gBrowser.browsers) {
+      if (window.gBrowser.getTabForBrowser(browser).linkedPanel) {
+        promises.push(this.flush(browser));
+      }
+    }
+    return Promise.all(promises);
+  },
+
+  /**
+   * Resolves the flush request with the given flush ID.
+   *
+   * @param browser (<xul:browser>)
+   *        The browser for which the flush is being resolved.
+   * @param flushID (int)
+   *        The ID of the flush that was sent to the browser.
+   * @param success (bool, optional)
+   *        Whether or not the flush succeeded.
+   * @param message (string, optional)
+   *        An error message that will be sent to the Console in the
+   *        event that a flush failed.
+   */
+  resolve(browser, flushID, success = true, message = "") {
+    // Nothing to do if there are no pending flushes for the given browser.
+    if (!this._requests.has(browser.permanentKey)) {
+      return;
+    }
+
+    // Retrieve active requests for given browser.
+    let { perBrowserRequests } = this._requests.get(browser.permanentKey);
+    if (!perBrowserRequests.has(flushID)) {
+      return;
+    }
+
+    if (!success) {
+      Cu.reportError("Failed to flush browser: " + message);
+    }
+
+    // Resolve the request with the given id.
+    let resolve = perBrowserRequests.get(flushID);
+    perBrowserRequests.delete(flushID);
+    resolve(success);
+  },
+
+  /**
+   * Resolves all active flush requests for a given browser. This should be
+   * used when the content process crashed or the final update message was
+   * seen. In those cases we can't guarantee to ever hear back from the frame
+   * script so we just resolve all requests instead of discarding them.
+   *
+   * @param browser (<xul:browser>)
+   *        The browser for which all flushes are being resolved.
+   * @param success (bool, optional)
+   *        Whether or not the flushes succeeded.
+   * @param message (string, optional)
+   *        An error message that will be sent to the Console in the
+   *        event that the flushes failed.
+   */
+  resolveAll(browser, success = true, message = "") {
+    // Nothing to do if there are no pending flushes for the given browser.
+    if (!this._requests.has(browser.permanentKey)) {
+      return;
+    }
+
+    // Retrieve the cancel function for a given browser.
+    let { cancel } = this._requests.get(browser.permanentKey);
+
+    if (!success) {
+      Cu.reportError("Failed to flush browser: " + message);
+    }
+
+    // Resolve all requests.
+    cancel(success);
+  },
+};