multi doesn't handle responses properly

[fcheung]

Dalli's multi method doesn't seem to handle responses as it should. The following snippet demonstrates the problem I've observed

dalli.set('foo', 'bar')
dalli.multi { dalli.delete 'keythatdoesnotexist'}
dalli.get 'foo' #=> returns true !
dalli.get 'foo' #=> returns 'bar' as expected

I'm not very familiar with the memcached protocol, and it's not really described in the protocol docs (other than in the getq) case, but it sounds:

• quiet ops suppress non interesting responses
• quiet ops delay starting to send a response until a non quiet response is sent.

Since this isn't happening in the above, the interesting responses from the dalli.multi block only get sent when the get request is made & dalli ends up returning the response from the failed delete as the get request.

Ideally (for me at least). multi would take care of this by sending a noop request and reading any response data, but this would mean that all existing uses of multi would incur one extra request. At the very least this should be called out in the docs, ideally with the addition of a read_responses option to multi.

The noop method on Server nearly does the right thing, although it assumes that all response are KV responses whereas they could be of any type (in addition this functionality isn't exposed on Client).

Happy to work on this if a direction is agreed.

[moxley]

I'm getting similar results:

dalli.set('foo', 'bar')
dalli.multi { dalli.delete 'keythatdoesnotexist'}
dalli.get 'foo' #=> returns nil. should have been 'bar'
dalli.get 'foo' #=> returns 'bar' as expected

dalli.set('foo', 'bar')
dalli.multi { dalli.delete 'keythatdoesnotexist'}
dalli.get 'foo' #=> returns true, should have been 'bar'
dalli.get 'foo' #=> returns nil, should have been 'bar'

dalli.set('foo', 'bar')
dalli.multi { dalli.delete 'keythatdoesnotexist'}
dalli.get 'foo' #=> returns "bar"
dalli.get 'foo' #=> returns 'bar'

[kamaljoshi]

This seems to be related to this: #321

It seems the response is available with the socket but because the multi command doesn't end up reading it. It gets read with the next request according to bin protocol and only the response to the last request is returned.

dalli.set('foo', 'bar')
dalli.multi { dalli.delete 'keythatdoesnotexist'}
dalli.send(:ring).servers.each {|server| p server.sock.read_available} #=> "\x81\x14\x00\x00\x00\x00\x00\x01\x00\x00\x00\t\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00Not found"

It kind of makes multi unusable.