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Issue
240133005:
Mojo: Make some attempts towards fixing remote message pipe closure. (Closed)
DescriptionMojo: Make some attempts towards fixing remote message pipe closure.
It's not quite right yet (I still need to fix how they get started -- i.e.,
attached and run -- since that races in a poor way with how they get closed),
but I think I'm getting closer.
There's an intentional cycle of ref-counted objects, between the
ProxyMessagePipeEndpoint and the Channel, which needs to be broken when
one of the (real) endpoints of the message pipe is closed. The picture
is:
LocalMPE-ProxyMPE-Channel <-----> Channel-ProxyMPE-LocalMPE
When a LocalMessagePipeEndpoint is closed, ultimately the other
LocalMessagePipeEndpoint needs to be informed ("OnPeerClosed"), and the
two ProxyMessagePipeEndpoints can be torn down.
There are many difficulties, however. First, while a
ProxyMessagePipeEndpoint may be torn down, its entry (with its local ID)
may not be removed from the Channel until it's known that the other side
will not send messages to that ID (because you can't re-use that ID
until then). Basically, this amounts to notifying the other side and
receiving an ack. (We can mark the entry in the Channel with a suitable
"zombie" state to handle this.)
Second, both LocalMessagePipeEndpoints may be closed "simultaneously" --
resulting in the removal notification messages "crossing paths". Of
course, once you receive a removal notification for a given ID, you know
the other side will not send any more messages to that ID. So, there's
no need to send an ack in that case.
Now, there are lock order issues, so that removal of an ID from a
channel (upon receiving a removal message) races with the
LocalMessagePipeEndpoint (on the "local" side) being closed, so you have
to handle that.
Then there are races with the ProxyMessagePipeEndpoint being attached
and run (and possibly receiving a removal message). (This CL doesn't
address all those issues.)
Finally, note that sometimes you have to keep the
ProxyMessagePipeEndpoint alive past "OnPeerClose". E.g., it's valid for
you to write a whole bunch of messages to a MessagePipe endpoint, and
then immediately close it. The ProxyMessagePipeEndpoint must stay alive
until it's been attached/run and sent out all those messages (and a
remove message).
R=darin@chromium.org
BUG=360081
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=264716
Patch Set 1 #
Total comments: 4
Patch Set 2 : review comments #Patch Set 3 : fix some locking issues #
Messages
Total messages: 10 (0 generated)
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