Merge pull request #3615 from lightpanda-io/reduce-v8-background-execution-delay

perf: reduce delay in running v8 background jobs

src/browser/Browser.zig

@@ -262,14 +262,15 @@ pub fn runMicrotasks(self: *Browser) void {
     self.env.runMicrotasks();
 }
 
-pub fn runMacrotasks(self: *Browser) !void {
+pub fn runMacrotasks(self: *Browser) !bool {
     const env = &self.env;
 
     try self.env.runMacrotasks();
-    env.pumpMessageLoop();
+    const ran_platform_task = env.pumpMessageLoop();
 
     // either of the above could have queued more microtasks
     env.runMicrotasks();
+    return ran_platform_task;
 }
 
 pub fn hasBackgroundTasks(self: *Browser) bool {

src/browser/Runner.zig

@@ -35,6 +35,7 @@ const Runner = @This();
 session: *Session,
 browser: *Browser,
 http_client: *HttpClient,
+background_poll_ms: u32 = 0,
 
 pub const Opts = struct {};
 
@@ -223,8 +224,9 @@ fn _tick(self: *Runner, comptime is_cdp: bool, timeout_ms: u32, conditions: []Wa
 
     const has_runnable_page = hasRunnablePage(session);
 
+    var ran_platform_task = false;
     if (has_runnable_page) {
-        try browser.runMacrotasks();
+        ran_platform_task = try browser.runMacrotasks();
     }
 
     const activity = http_client.activity();
@@ -318,8 +320,16 @@ fn _tick(self: *Runner, comptime is_cdp: bool, timeout_ms: u32, conditions: []Wa
                 break :blk 200;
             }
             if (browser.hasBackgroundTasks()) {
+                // if our last runMacrotasks() ran something and we now have
+                // a background, then don't linger in the http client waiting
+                // for I/O, instead, hurry back to run more tasks.
+                // Else, backoff to 10ms between runs.
+                // TODO: this is a temporary solution to ensuring background
+                // tasks are run promptly.The better solution is to have v8
+                // wakeup the http client when there's work to do.
+                self.background_poll_ms = if (ran_platform_task) 0 else @min(10, @max(1, self.background_poll_ms * 2));
                 // msToNextTask could be less than this, but 10ms drift is ok
-                break :blk 10;
+                break :blk self.background_poll_ms;
             }
             break :blk browser.msToNextTask() orelse 200;
         };

src/browser/js/Env.zig

@@ -567,14 +567,18 @@ pub fn msToNextTask(self: *Env) ?u64 {
     return if (next_task == std.math.maxInt(u64)) null else next_task;
 }
 
-pub fn pumpMessageLoop(self: *const Env) void {
+pub fn pumpMessageLoop(self: *const Env) bool {
     var hs: v8.HandleScope = undefined;
     v8.v8__HandleScope__CONSTRUCT(&hs, self.isolate.handle);
     defer v8.v8__HandleScope__DESTRUCT(&hs);
 
     const isolate = self.isolate.handle;
     const platform = self.platform.handle;
-    while (v8.v8__Platform__PumpMessageLoop(platform, isolate, false)) {}
+    var ran = false;
+    while (v8.v8__Platform__PumpMessageLoop(platform, isolate, false)) {
+        ran = true;
+    }
+    return ran;
 }
 
 pub fn hasBackgroundTasks(self: *const Env) bool {

src/browser/js/Local.zig

@@ -121,7 +121,7 @@ pub fn newCallback(
 
 pub fn runMacrotasks(self: *const Local) void {
     const env = self.ctx.env;
-    env.pumpMessageLoop();
+    _ = env.pumpMessageLoop();
     env.runMicrotasks(); // macrotasks can cause microtasks to queue
 }