On Sun, Mar 3, 2013 at 5:08 PM, Noah Watkins <jayhawk@xxxxxxxxxxx> wrote:
>
> I've built a custom protocol on top of Rados::exec that uses serialized
> versions of InputObject and OutputObject to implement the protocol. Here's
> simple pseudo-code that provides my_service::exec:
>
> void my_service::exec(oid, input_params, bufferlist& out) {
> bufferlist inbl, outbl;
> InputObject in(input_params);
> ::encode(in, inbl);
>
> librados::exec(oid, inbl, outbl);
>
> OutputObject reply;
> ::decode(reply, outbl);
> out = reply.payload;
> }
>
> I'd like to provide a my_service::aio_exec that wraps librados::aio_exec,
> but doing so doesn't seem to be straight-forward with the current async
> interface.
>
> Notice in the above example that the callers output bufferlist must be
> unpacked from the reply protocol. However, the librados::aio_exec interface
> unpacks the output directly into the caller parameter:
>
> int librados::aio_exec(oid, …, bufferlist *outbl)
> {
> ...
> objecter->read(oid, oloc, rd, snap_seq, outbl, 0, onack, &c->objver);
> }
>
> What's needed is a intermediate bufferlist that can be decoded when the
> data is available.
>
> One way to do this would be wrap AioCompletion and intercept ack and safe
> callbacks to do the data unpacking. The problem with this is that we have to
> introduce a new AioCompletion type, or new AioCompletionImpl. I started to
> do this, but it feels quite clunky.
>
> Any suggestions for handling this?
>
I pushed the wip-librados-exec branch last week that solves a similar
issue. I added two more ObjectOperation::exec() api calls. The more
interesting one added a callback context that is called with the
output buffer of the completed sub-op. Currently in order to use it
you'll need to use operate()/aio_operate(), however, a similar
aio_exec interface can be added.
Yehuda
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