889881 - ANR: GeckoAppShell.pumpMessageLoop() can block the Gecko thread

Status: RESOLVED FIXED

(Firefox for Android Graveyard :: General, defect)

Description

[(inactive) Jim Chen [:jchen] [:darchons]]

GeckoAppShell.pumpMessageLoop() calls GeckoAppShell.getNextMessageFromQueue() through JNI to retrieve the next message from the Gecko thread message queue. Because we don't want MessageQueue.next() to block, getNextMessageFromQueue() bails if |MessageQueue.mMessages == null|. However that's not a reliable way to detect whether MessageQueue.next() will block or not, and it can still block if there are pending messages (e.g. delayed messages). Once MessageQueue.next() blocks, the Gecko thread is blocked, causing unresponsiveness and ANRs.

Comment 1

[(inactive) Jim Chen [:jchen] [:darchons]]

Attachment: Refactor and add a Gecko handler to ThreadUtils (v1)

We first need a Gecko handler in order for the fix to work. This patch also moves setting the Gecko thread/handler to inside GeckoThread.

Comment 2

[(inactive) Jim Chen [:jchen] [:darchons]]

Attachment: Use IdleHandler to make MessageQueue.next() not block (v1)

The fix here uses an IdleHandler to detect when MessageQueue.next() is going to block or not, instead of checking MessageQueue.mMessages. The IdleHandler cannot throw an Exception to prevent blocking, but it can queue a new, special message. This new message gets returned in MessageQueue.next() and we return early when we detect this message (this patch uses Message.obj to set/detect the special message).

Comment 3

[Brad Lassey [:blassey] (use needinfo?)]

Comment on attachment 770844 [details] [diff] [review]
Use IdleHandler to make MessageQueue.next() not block (v1)

Review of attachment 770844 [details] [diff] [review]:
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Not going to lie, there is some black magic in this code. Let's keep an eye out for flash bugs after this lands.

Comment 4

[(inactive) Jim Chen [:jchen] [:darchons]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/66427620c3cd
https://hg.mozilla.org/integration/mozilla-inbound/rev/487b02e3c084

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/66427620c3cd
https://hg.mozilla.org/mozilla-central/rev/487b02e3c084