Load web fonts synchronously during wpt.

3 files changed, 24 insertions, 5 deletions

diff --git a/components/layout/layout_task.rs b/components/layout/layout_task.rs
index c86ecdedaff..7a615b02f6b 100644
--- a/components/layout/layout_task.rs
+++ b/components/layout/layout_task.rs
@@ -326,10 +326,18 @@ fn add_font_face_rules(stylesheet: &Stylesheet,
                        outstanding_web_fonts_counter: &Arc<AtomicUsize>) {
     for font_face in stylesheet.effective_rules(&device).font_face() {
         for source in &font_face.sources {
-            outstanding_web_fonts_counter.fetch_add(1, Ordering::SeqCst);
-            font_cache_task.add_web_font(font_face.family.clone(),
-                                         (*source).clone(),
-                                         (*font_cache_sender).clone());
+            if opts::get().load_webfonts_synchronously {
+                let (sender, receiver) = channel();
+                font_cache_task.add_web_font(font_face.family.clone(),
+                                             (*source).clone(),
+                                             sender);
+                receiver.recv().unwrap();
+            } else {
+                outstanding_web_fonts_counter.fetch_add(1, Ordering::SeqCst);
+                font_cache_task.add_web_font(font_face.family.clone(),
+                                             (*source).clone(),
+                                             (*font_cache_sender).clone());
+            }
         }
     }
 }
diff --git a/components/util/opts.rs b/components/util/opts.rs
index fb68c24964d..6d91e0d6c42 100644
--- a/components/util/opts.rs
+++ b/components/util/opts.rs
@@ -74,6 +74,9 @@ pub struct Opts {
     /// Log GC passes and their durations.
     pub gc_profile: bool,
 
+    /// Load web fonts synchronously to avoid non-deterministic network-driven reflows.
+    pub load_webfonts_synchronously: bool,
+
     pub headless: bool,
     pub hard_fail: bool,
 
@@ -267,6 +270,9 @@ pub struct DebugOptions {
 
     /// Log GC passes and their durations.
     pub gc_profile: bool,
+
+    /// Load web fonts synchronously to avoid non-deterministic network-driven reflows.
+    pub load_webfonts_synchronously: bool,
 }
 
 
@@ -301,6 +307,7 @@ impl DebugOptions {
                 "convert-mouse-to-touch" => debug_options.convert_mouse_to_touch = true,
                 "replace-surrogates" => debug_options.replace_surrogates = true,
                 "gc-profile" => debug_options.gc_profile = true,
+                "load-webfonts-synchronously" => debug_options.load_webfonts_synchronously = true,
                 "" => {},
                 _ => return Err(option)
             };
@@ -345,6 +352,8 @@ pub fn print_debug_usage(app: &str) -> ! {
     print_option("replace-surrogates", "Replace unpaires surrogates in DOM strings with U+FFFD. \
                                         See https://github.com/servo/servo/issues/6564");
     print_option("gc-profile", "Log GC passes and their durations.");
+    print_option("load-webfonts-synchronously",
+                 "Load web fonts synchronously to avoid non-deterministic network-driven reflows");
 
     println!("");
 
@@ -414,6 +423,7 @@ pub fn default_opts() -> Opts {
         output_file: None,
         replace_surrogates: false,
         gc_profile: false,
+        load_webfonts_synchronously: false,
         headless: true,
         hard_fail: true,
         bubble_inline_sizes_separately: false,
@@ -632,6 +642,7 @@ pub fn from_cmdline_args(args: &[String]) {
         output_file: opt_match.opt_str("o"),
         replace_surrogates: debug_options.replace_surrogates,
         gc_profile: debug_options.gc_profile,
+        load_webfonts_synchronously: debug_options.load_webfonts_synchronously,
         headless: opt_match.opt_present("z"),
         hard_fail: opt_match.opt_present("f"),
         bubble_inline_sizes_separately: bubble_inline_sizes_separately,
diff --git a/tests/wpt/harness/wptrunner/executors/executorservo.py b/tests/wpt/harness/wptrunner/executors/executorservo.py
index a1e0ea97b31..b1beea9934a 100644
--- a/tests/wpt/harness/wptrunner/executors/executorservo.py
+++ b/tests/wpt/harness/wptrunner/executors/executorservo.py
@@ -203,7 +203,7 @@ class ServoRefTestExecutor(ProcessTestExecutor):
             debug_args, command = browser_command(
                 self.binary,
                 [render_arg(self.browser.render_backend), "--hard-fail", "--exit",
-                 "-u", "Servo/wptrunner", "-Z", "disable-text-aa",
+                 "-u", "Servo/wptrunner", "-Z", "disable-text-aa,load-webfonts-synchronously",
                  "--output=%s" % output_path, full_url],
                 self.debug_info)