FAQ
I'm not sure we are on the same page, because I think in this case there is
no race, at least the question is not about a possible race condition.
I know about race detector and I'm agree that's a pretty awesome tool.
In a very simple form, the question is that the net.Conn is work in FIFO or
not, but in this form it maybe misleading, that's why I tried to explain
the whole story. :)
On Saturday, October 25, 2014 6:41:46 PM UTC+2, Kevin Malachowski wrote:

The race-detector <https://blog.golang.org/race-detector> is a pretty
awesome tool that allows you to easily find out if you're making the wrong
assumptions about concurrent code and also even better for catching
outright mistakes. Try whipping up a short example that attempts to do what
you're doing and run it under the race detector. If it passes, it doesn't
have any races. If it fails, you will need to do things a different way
because races are by definition non-deterministic and that's a bad thing.

When I deal with network connections I usually end up with a goroutine
reading and a separate goroutine writing, unless the protocol I'm
implementing is a simple call-response like HTTP (in which case it's one
goroutine per connection that alternates listening and writing). I use the
concurrency primitives (channels, waitgroups, mutexes, etc) to allow the
reader and writer to communicate between themselves as well as with other
goroutines that may exist. It allows me to immediately abstract away the
annoyance that is dealing with a primitive byte stream and therefore
integrates into other code better.
On Saturday, October 25, 2014 2:33:43 AM UTC-7, Norbert Csibra wrote:

Hi,

I'm trying to implement scgi protocol support to an existing xmlrpc
library, using a custom rpc.ClientCodec.
My problem is, that the ClientCodec in the ReadResponseHeader expecting
to set at least the "Seq" field of the Response struct.
As I understand from the source, it must match with the original "Seq"
from the Request, otherwise may the wrong "Call" will return to the client.
The problem is, that the xmlrpc response does not provide the "Seq"
number, neither the original "ServiceMethod" or arguments.
So if 2 rpc method invoked through the same Client from multiple
goroutine, I can't identify in the response which one returned.
The obvious solution to do the calls sequentially, communicating between
the "WriteRequest" and "ReadResponseHeader" calls with a channel for
example, but it's ugly.

I thinking an other way, where creating a struct, saving the "Seq" and
"ServiceMethod" and fire a separate goroutine, which do the call and read
the response, save it to the same struct, then send it to the
"ReadResponseHeader" method, through a channel.
This way I could be able to match the responses and the "Seq" id-s, I'm
unsure only one thing.
The documentation of the net.Conn says, "Multiple goroutines may invoke
methods on a Conn simultaneously", which is good, but what if:
Calling a long running rpc method from the A goroutine and a short
running one from the B goroutine.
It means the "WriteRequest" will be invoked 2 times, so I creating 2
struct, e.g.: with "Seq" 0(A) and 1(B) and trying to read the responses
from 2 separate goroutine.
I assume(depend from the server) it would be possible that the goroutine
with "Seq" 0 read the response of the "Seq" 1 request, because the server
finish earlier with the shorter rpc method.
In this case, 2 goroutine waits to read from the connection and when it's
ready to receive, the go scheduler will pick one randomly, so may the
responses will reverse.
Am I right?
If so, is there a way to make the rpc calls concurrent safely, without
reversing the responses?

Thanks,
Norbert
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