v8::Isolate::GetCurrent()->IdleNotificationDeadline not working in 3.x (manual gc not working)

[marcominetti]

Hi there, I'm currently maintaining the node-memwatch package against latest iojs/nodejs versions, available as memwatch-next on npm.

I've noticed that with new v8 version 4.4.63.26 the IdleNotification does not trigger GC at all.

I'm using both NaN 2.0.5 and direct v8::Isolate::GetCurrent()->IdleNotificationDeadline call with 500ms, 1s and 5s.

The gc seems not to be executed. I can make it run successfully with --expose-gc flag through the global.gc() function.

[marcominetti]

example code (from memwatch):

NAN_METHOD(memwatch::trigger_gc) {
    Nan::HandleScope scope;
    while(!(v8::Isolate::GetCurrent()->IdleNotificationDeadline(0.500))) {};

    //while(!Nan::IdleNotification(500)) {};

    info.GetReturnValue().Set(Nan::Undefined());
}

[bnoordhuis]

Do you start iojs with --use_idle_notification? It's a complete no-op without that flag.

[marcominetti]

I supposed that flag was enabled by default... I'll try when back to the office.

Has been changed something in iojs 3.x? Everything works fine till 2.5.0 branch.

[bnoordhuis]

I take back what I said, I see that --use_idle_notification is on by default. Does v8::Isolate::IdleNotification() work?

[marcominetti]

Nope. Seems something not working in v8...

[marcominetti]

Should we suppose the strategy to call

while(!(v8::Isolate::GetCurrent()->IdleNotificationDeadline(0.500))) {};

is deprecated cause new IdleNotification implementation does not returns true as consistently as before?

[kkoopa]

That is probably a safe assumption. IIRC, there was never a guarantee of this triggering garbage collection. Only reliable way is by the functionality exposed with --expose-gc.

[Fishrock123]

Closing unless there is actually something we can do about this and/or should. :)