1212906 - avoid handling windows messages while waiting for the responseto a sync a11y message

Status: RESOLVED FIXED

(Core :: IPC, defect)

Comment 1

[Trevor Saunders (:tbsaunde)]

Attachment: don't handle windows messages while waiting for a sync a11y ipc message

Windows messages can trigger sync ipc messages to the child process.  That
means if we handle windows messages while waiting for the response to a sync
a11y ipc message we can end up reentering the code to send ipc messages which
is bad.  Try and avoid this situation by not handling windows messages while
waiting for a sync a11y message.

Comment 2

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

Comment on attachment 8671432 [details] [diff] [review]
don't handle windows messages while waiting for a sync a11y ipc message

Review of attachment 8671432 [details] [diff] [review]:
-----------------------------------------------------------------

Looks good. Thanks.

::: dom/ipc/ContentParent.cpp
@@ +5477,5 @@
> +
> +bool
> +ContentParent::HandleWindowsMessages(const Message& aMsg) const
> +{
> +  if (!aMsg.is_sync()) {

Please MOZ_ASSERT(aMsg.is_sync())

::: ipc/glue/MessageLink.h
@@ +98,5 @@
>          return RIPChildWins;
>      }
>  
> +    /**
> +     * Return true if windows messages can be handled while waiting for a reply

Please replace 'can' with 'should'.

Comment 3

[Trevor Saunders (:tbsaunde)]

> ::: dom/ipc/ContentParent.cpp
> @@ +5477,5 @@
> > +
> > +bool
> > +ContentParent::HandleWindowsMessages(const Message& aMsg) const
> > +{
> > +  if (!aMsg.is_sync()) {
> 
> Please MOZ_ASSERT(aMsg.is_sync())

is that actually true? I'd think MessageChannel::Send() could call this for async messages too (though maybe we should avoid that there?)

Comment 4

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

MessageChannel::Send(Message* aMsg, Message* aReply) is only called for sync messages. There's a separate overload without a reply parameter that's used for async messages.

Comment 5

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/f753f2c6e79c

Comment 6

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/f753f2c6e79c