951671 - Periodic Worker activity during idle (osfile_async_worker.js, SessionWorker.js, PageThumbsWorker.js)

Status: RESOLVED FIXED

(Core :: DOM: Workers, defect)

Description

[Roberto Agostino Vitillo (:rvitillo)]

To reproduce:
1) recompile dom/workers/WorkerPrivate.cpp with -DWORKER_LOGGING
2) launch firefox, open about:blank and minimize the window
3) observe the periodic activity, e.g:
   Worker 0x10dbaec00 collected idle garbage
   Worker 0x10dbaec00 canceled GC timer because idle
   Worker 0x10dbaec00 scheduled idle GC timer

Comment 1

[Boris Zbarsky [:bzbarsky]]

This seems like workers, not jseng....

Comment 2

[Ben Turner (not reading bugmail, use the needinfo flag!)]

What's the bug here? Every time a worker is used we schedule followup GCs. That seems normal to me.

Comment 3

[Roberto Agostino Vitillo (:rvitillo)]

Right. The question is then what are those workers doing during idle. On my machine I measured up to 20 wakeups per minute, due to workers, during a ten minutes idle run.

Comment 4

[Ben Turner (not reading bugmail, use the needinfo flag!)]

Ah, ok. That should be easy enough to pin down. Is this on desktop firefox or b2g?

Comment 5

[Roberto Agostino Vitillo (:rvitillo)]

It's on desktop firefox.

Comment 6

[Ben Turner (not reading bugmail, use the needinfo flag!)]

Ok, great! The simplest way to do this is probably modify the printfs that are triggered with the -DWORKER_LOGGING switch. Just make them additionally dump the mScriptURL member and it should be easy to tell which worker is waking up all the time.

Comment 7

[Roberto Agostino Vitillo (:rvitillo)]

The culprits are ///modules/sessionstore/SessionWorker.js and //gre/modules/osfile/osfile_async_worker.js.

Comment 8

[David Teller [:Yoric] - still alive but not very active]

Normally, neither thread has any activity unless there is something on the main thread requesting that something be done. If more information is needed, we can activate OS.File logging, by setting preference "toolkit.osfile.log" to true.

Comment 9

[Ben Turner (not reading bugmail, use the needinfo flag!)]

I'll move this over to the session storage component.

Comment 10

[David Teller [:Yoric] - still alive but not very active]

The common point between all these workers is OS.File, so moving again.

I have Nightly currently running on idle, and OS.File doesn't seem to receive any messages. Since there is no code in OS.File (or in any of these threads) that causes any activity without messages, I'm tempted to think that the problem is either in js-ctypes or in workers, though.

Comment 11

[David Teller [:Yoric] - still alive but not very active]

I can reproduce here. OS.File isn't receiving any message but we get
2045159776[100462660]: THRD(1004407c0) ProcessNextEvent [0 0]
2045159776[100462660]: THRD(1004407c0) running [113968170]
2045159776[100462660]: [this=113968170] time between PostTimerEvent() and Fire(): 0.200333ms
2045159776[100462660]: [this=1143ed5e0] expected delay time 60000ms
2045159776[100462660]: [this=1143ed5e0] actual delay time   60001.915000ms
2045159776[100462660]: [this=1143ed5e0] (mType is 1)       -------
2045159776[100462660]: [this=1143ed5e0]     delta              1ms
2045159776[100462660]: [this=1143ed5e0] Took 0.233058ms to fire timer callback
etc.

Comment 12

[Roberto Agostino Vitillo (:rvitillo)]

The workers are indeed not doing any activity. What seems to be happening here is the following:

1) an idle GC timer is fired which causes a GarbageCollectRunnable to be dispatched (http://hg.mozilla.org/mozilla-central/file/7a1445739c07/dom/workers/WorkerPrivate.cpp#l1407) and enqueued in the ControlQueue (http://hg.mozilla.org/mozilla-central/file/7a1445739c07/dom/workers/WorkerPrivate.cpp#l2239)
2) the GarbageCollectRunnable is processed (http://hg.mozilla.org/mozilla-central/file/7a1445739c07/dom/workers/WorkerPrivate.cpp#l3970) in the worker’s event loop
3) an idle GC timer is set with a delay of 5 seconds (http://hg.mozilla.org/mozilla-central/file/7a1445739c07/dom/workers/WorkerPrivate.cpp#l4028);
4) goto 1.

Is there a reason why garbage collection should be performed when a worker isn’t doing any activity?

Comment 13

[Ben Turner (not reading bugmail, use the needinfo flag!)]

Attachment: Patch, v1

Hm, looks like I missed this somehow!

Comment 14

[Ben Turner (not reading bugmail, use the needinfo flag!)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/9c3731bf49a7

Comment 15

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/9c3731bf49a7