717027 - IPDL compiler doesn't generate code to handle message type SHMEM_CREATED_MESSAGE_TYPE when no other async messages are declared

Status: RESOLVED FIXED

(Core :: IPC, defect)

Description

[Ali Juma [:ajuma]]

When the declaration of a manager protocol doesn't include any async messages received by the parent, the ipdl compiler does not generate code to handle messages of type SHMEM_CREATED_MESSAGE_TYPE in Parent::OnMessageReceived(Message&). A workaround is simply adding an (unused) async message to the protocol declaration.

Comment 1

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

That is ... most odd.  I don't have a guess for what's up.  Probably an easy fix.

Comment 2

[Ali Juma [:ajuma]]

The problem is related to lines 2885-2890 of ipc/ipdl/ipdl/lower.py:

            if switch.nr_cases > 1:
                method.addstmt(switch)
            else:
                method.addstmt(StmtReturn(_Result.NotKnown))

When a protocol has no async messages declared, at the point at which this snippet gets executed (during the generation of Parent.cpp::OnMessageReceived(Message&)) the only case added to |switch| (which is self.asyncSwitch here) is the default case, so |switch| doesn't get added to the method. Then, lines 3530-3536 (which add the SHMEM_CREATED/DESTROYED handlers to self.asyncSwitch) have no effect on the generated method.

Indeed, changing line 2885 to:

            if switch.nr_cases > 0:

fixes the problem (but breaks bug 509581).

Comment 3

[Ali Juma [:ajuma]]

An example of a protocol where we have to work around this bug is PCompositor.ipdl in Attachment 587713 [details] [diff], Bug 711168.

Comment 4

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

OK, that makes sense.  The control flow is way too hard to follow in there.

The simplest fix looks like moving

        # FIXME/bug 535053: only manager protocols and non-manager
        # protocols with union types need Lookup().  we'll give it to
        # all for the time being (simpler)
        if 1 or ptype.isManager():
            self.cls.addstmts(self.implementManagerIface())

before 

        def makeHandlerMethod(name, switch, hasReply, dispatches=0):
            params = [ Decl(Type('Message', const=1, ref=1), msgvar.name) ]

The "right" fix is to rewrite this code again :/.

Comment 5

[Ali Juma [:ajuma]]

Attachment: Make IPDL compiler generate code to handle SHMEM-related messages even when there are no other async messages

This implements the fix from Comment 4.

Comment 6

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Comment on attachment 588131 [details] [diff] [review]
Make IPDL compiler generate code to handle SHMEM-related messages even when there are no other async messages

It would extremely gross to write a test for this, and not all that incredibly useful IMHO, so r=me without that.

Comment 7

[Ali Juma [:ajuma]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/f9413ba08c26

Comment 8

[Marco Bonardo [:mak]]

https://hg.mozilla.org/mozilla-central/rev/f9413ba08c26