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Run the MessageLoop [a lot] more.

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Depends on: https://github.com/lightpanda-io/zig-v8-fork/pull/152

We previously ran the message loop every 250ms. This commit changes it to run on
every tick (much more frequently). It also runs microtasks after draining the
message loop (since it can generate microtasks).

Also, we use to run microtasks after each script execution. Now we drain the
message Loop + microtasks.

We still only drain the microtasks when executing v8 callbacks.

As part of this change, we also adjust our wait time based on whether or not
there are pending background tasks in v8 in order to try to execute them (in
general) and in a timely manner.

The goal is to ensure that tasks v8 enqueued on the foreground thread are
executed promptly.

This change is particularly useful for calls to webassembly as compilation
happens in the background and eventually requires the message loop to be drained
to continue.

Previously, if a script did `await WebAssembly.instantiate(....)`, there was
a good chance we'd never finish the code - we'd wait too long to run the
message loop AND, after running it, we wouldn't necessarily resolve the promise.
This commit is contained in:
Karl Seguin
2026-02-25 13:55:35 +08:00
parent a041162b32
commit af7498d283
9 changed files with 71 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
build.zig.zon
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@@ -6,8 +6,9 @@
.minimum_zig_version = "0.15.2",
.dependencies = .{
.v8 = .{
.url = "https://github.com/lightpanda-io/zig-v8-fork/archive/refs/tags/v0.3.0.tar.gz",
.hash = "v8-0.0.0-xddH69R6BADRXsnhjA8wNnfKfLQACF1I7CSTZvsMAvp8",
.url = "https://github.com/lightpanda-io/zig-v8-fork/archive/8c7e5df8b93e7cbd42f8f1c4ac24aaa7f05cd098.tar.gz",
.hash = "v8-0.0.0-xddH64J7BAC81mkf6G9RbEJxS-W3TIRl5iFnShwbqCqy",
},
//.v8 = .{ .path = "../zig-v8-fork" },
.@"boringssl-zig" = .{

20
src/browser/Browser.zig
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@@ -92,10 +92,24 @@ pub fn runMicrotasks(self: *Browser) void {
}
pub fn runMacrotasks(self: *Browser) !?u64 {
return try self.env.runMacrotasks();
const env = &self.env;
const time_to_next = try self.env.runMacrotasks();
env.pumpMessageLoop();
// either of the above could have queued more microtasks
env.runMicrotasks();
return time_to_next;
}
pub fn runMessageLoop(self: *const Browser) void {
self.env.pumpMessageLoop();
pub fn hasBackgroundTasks(self: *Browser) bool {
return self.env.hasBackgroundTasks();
}
pub fn waitForBackgroundTasks(self: *Browser) void {
self.env.waitForBackgroundTasks();
}
pub fn runIdleTasks(self: *const Browser) void {
self.env.runIdleTasks();
}

8
src/browser/Page.zig
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@@ -311,12 +311,12 @@ pub fn init(self: *Page, id: u32, session: *Session, parent: ?*Page) !void {
if (comptime builtin.is_test == false) {
// HTML test runner manually calls these as necessary
try self.js.scheduler.add(session.browser, struct {
fn runMessageLoop(ctx: *anyopaque) !?u32 {
fn runIdleTasks(ctx: *anyopaque) !?u32 {
const b: *@import("Browser.zig") = @ptrCast(@alignCast(ctx));
b.runMessageLoop();
return 250;
b.runIdleTasks();
return 200;
}
}.runMessageLoop, 250, .{ .name = "page.messageLoop" });
}.runIdleTasks, 200, .{ .name = "page.runIdleTasks", .low_priority = true });
}
}

3
src/browser/ScriptManager.zig
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@@ -862,8 +862,7 @@ pub const Script = struct {
}
defer {
// We should run microtasks even if script execution fails.
local.runMicrotasks();
local.runMacrotasks(); // also runs microtasks
_ = page.js.scheduler.run() catch |err| {
log.err(.page, "scheduler", .{ .err = err });
};

20
src/browser/Session.zig
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@@ -257,7 +257,7 @@ fn _wait(self: *Session, page: *Page, wait_ms: u32) !WaitResult {
std.debug.assert(http_client.intercepted == 0);
}
const ms = ms_to_next_task orelse blk: {
const ms: u64 = ms_to_next_task orelse blk: {
if (wait_ms - ms_remaining < 100) {
if (comptime builtin.is_test) {
return .done;
@@ -267,6 +267,14 @@ fn _wait(self: *Session, page: *Page, wait_ms: u32) !WaitResult {
// background jobs.
break :blk 50;
}
if (browser.hasBackgroundTasks()) {
// _we_ have nothing to run, but v8 is working on
// background tasks. We'll wait for them.
browser.waitForBackgroundTasks();
break :blk 20;
}
// No http transfers, no cdp extra socket, no
// scheduled tasks, we're done.
return .done;
@@ -292,8 +300,14 @@ fn _wait(self: *Session, page: *Page, wait_ms: u32) !WaitResult {
// an cdp_socket registered with the http client).
// We should continue to run lowPriority tasks, so we
// minimize how long we'll poll for network I/O.
const ms_to_wait = @min(200, @min(ms_remaining, ms_to_next_task orelse 200));
if (try http_client.tick(ms_to_wait) == .cdp_socket) {
var ms_to_wait = @min(200, ms_to_next_task orelse 200);
if (ms_to_wait > 10 and browser.hasBackgroundTasks()) {
// if we have bakcground tasks, we don't want ot wait too
// long for a message from the client. We want to go back
// to the top of the loop and run macrotasks.
ms_to_wait = 10;
}
if (try http_client.tick(@min(ms_remaining, ms_to_wait)) == .cdp_socket) {
// data on a socket we aren't handling, return to caller
return .cdp_socket;
}

2
src/browser/js/Context.zig
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@@ -237,7 +237,7 @@ pub fn deinit(self: *Context) void {
env.isolate.notifyContextDisposed();
// There can be other tasks associated with this context that we need to
// purge while the context is still alive.
env.pumpMessageLoop();
_ = env.pumpMessageLoop();
v8.v8__MicrotaskQueue__DELETE(self.microtask_queue);
}

19
src/browser/js/Env.zig
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@@ -397,10 +397,23 @@ pub fn pumpMessageLoop(self: *const Env) void {
const isolate = self.isolate.handle;
const platform = self.platform.handle;
while (v8.v8__Platform__PumpMessageLoop(platform, isolate, false)) {
if (comptime IS_DEBUG) {
log.debug(.browser, "pumpMessageLoop", .{});
while (v8.v8__Platform__PumpMessageLoop(platform, isolate, false)) {}
}
pub fn hasBackgroundTasks(self: *const Env) bool {
return v8.v8__Isolate__HasPendingBackgroundTasks(self.isolate.handle);
}
pub fn waitForBackgroundTasks(self: *Env) void {
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__Isolate__HasPendingBackgroundTasks(isolate)) {
_ = v8.v8__Platform__PumpMessageLoop(platform, isolate, true);
self.runMicrotasks();
}
}

6
src/browser/js/Local.zig
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@@ -82,6 +82,12 @@ pub fn createTypedArray(self: *const Local, comptime array_type: js.ArrayType, s
return .init(self, size);
}
pub fn runMacrotasks(self: *const Local) void {
const env = self.ctx.env;
env.pumpMessageLoop();
env.runMicrotasks(); // macrotasks can cause microtasks to queue
}
pub fn runMicrotasks(self: *const Local) void {
self.ctx.env.runMicrotasks();
}

9
src/cdp/cdp.zig
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@@ -436,17 +436,18 @@ pub fn BrowserContext(comptime CDP_T: type) type {
pub fn deinit(self: *Self) void {
const browser = &self.cdp.browser;
const env = &browser.env;
// Drain microtasks makes sure we don't have inspector's callback
// in progress before deinit.
browser.env.runMicrotasks();
env.runMicrotasks();
// resetContextGroup detach the inspector from all contexts.
// It append async tasks, so we make sure we run the message loop
// before deinit it.
browser.env.inspector.?.resetContextGroup();
browser.runMessageLoop();
browser.env.inspector.?.stopSession();
env.inspector.?.resetContextGroup();
_ = env.pumpMessageLoop();
env.inspector.?.stopSession();
// abort all intercepted requests before closing the sesion/page
// since some of these might callback into the page/scriptmanager