feat(core): update v8 to 146.8.0 with foreground task ownership#32771
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bartlomieju merged 10 commits intomainfrom Mar 18, 2026
Merged
feat(core): update v8 to 146.8.0 with foreground task ownership#32771bartlomieju merged 10 commits intomainfrom
bartlomieju merged 10 commits intomainfrom
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Updates the v8 crate to 146.8.0 which includes rusty_v8#1934. The custom V8 platform now receives ownership of foreground tasks via v8::Task and v8::IdleTask types, instead of tasks being queued in the default platform. This eliminates the need for PumpMessageLoop and lets deno_core run V8 foreground tasks directly on the event loop. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Instead of manually queuing tasks in a registry and draining them in the event loop, spawn them directly onto the isolate's tokio runtime handle. This removes the timer thread, task queues, and the PumpMessageLoop call entirely. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Verifies that V8 foreground tasks are delivered to the correct isolate when multiple workers use Atomics.waitAsync concurrently. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Some unit tests and snapshot creation run JsRuntime without a tokio runtime. Use try_current() to gracefully skip waker registration instead of panicking. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
devsnek
reviewed
Mar 16, 2026
libs/core/runtime/setup.rs
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| if let Some(entry) = map.get(&key) { | ||
| let waker = entry.waker.clone(); | ||
| entry.handle.spawn(async move { | ||
| task.run(0.0); |
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v8 uses the value passed here like this for example:
while (deadline_in_seconds > platform_->MonotonicallyIncreasingTime()) {
so if you want the job to actually do anything you need to pass a value greater than the current monotonic timestamp.
in chromium all the idle tasks are queued together. and when there is idle time in the render process it will calculate a deadline and drain that queue until empty or it runs out of time.
this approach doesn't make much sense in server runtimes, so some other behavior needs to be selected i guess? but also worth noting is that in node the PostIdleTaskImpl just calls UNREACHABLE(), so maybe we don't need to care about it.
V8 idle tasks check `deadline > MonotonicallyIncreasingTime()`, so passing 0.0 makes them no-ops. Node also ignores idle tasks entirely. Just drop them without running. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Idle tasks are not used in server runtimes — Node also marks this as UNREACHABLE(). Panic if V8 ever posts one unexpectedly. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Immediate foreground tasks must run synchronously during the event loop poll to preserve microtask/timer ordering and ensure the event loop sees their effects before checking pending state. Delayed tasks use tokio::spawn with tokio::time::sleep. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
- Remove `pump_v8_message_loop` from `PollEventLoopOptions` — foreground tasks are now always drained unconditionally on every event loop tick. - Share the `ForegroundTaskQueue` (Arc<Mutex<Vec<v8::Task>>>) between `JsRuntimeState` and the global platform registry so the event loop drains tasks from its local Arc without touching the global map. - Delayed tasks now queue into the shared Vec after sleeping instead of running directly on a tokio worker thread, ensuring they execute on the isolate's foreground thread. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Remove needless `..Default::default()` now that the struct has only one field. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
devsnek
approved these changes
Mar 18, 2026
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Summary
v8crate from 146.5.0 to 146.8.0 (includes rusty_v8#1934)DenoPlatformImplto receivev8::Task/v8::IdleTaskownership from the C++ custom platform, instead of tasks being queued inDefaultPlatformPumpMessageLoopTest plan
cargo checkpasses (full workspace)tools/format.jscleantools/lint.jscleantest_pump_message_loopandatomics_wait_async_notifyspec tests validate foreground task delivery🤖 Generated with Claude Code