implement pserver RPC part, and simple parameter partition.

[helinwang]

Easier to view using github split diff :)

Please use the following command to build, because there is some problem with the go cmake (the cmake checks out a new Paddle from github for Go dependency, so the changes in local filesystem are not reflected. Fix is in another PR: #2294).

cd Paddle/paddle/go/cclient
mkdir build && cd build
mkdir -p go/src/github.com/PaddlePaddle; ln -s $GOPATH/src/github.com/PaddlePaddle/Paddle go/src/github.com/PaddlePaddle/
cmake .. && make
go run ../../cmd/pserver/pserver.go -p 3000 # run pserver

open new teminal and run:

./test/main # run the example program we just build

[dzhwinter]

type switch for clearly?

[helinwang]

I thought this is clear because the underlying type for selector is bool, but I could be wrong.
I don't fully understand how to do type switch here, could you paste the code here?

[dzhwinter]

maybe we should implement this interface bases on ectd? for example, list pserver names from etcd value for fault tolerant pserver?

[helinwang]

I will write a module who implements this interface that talks to etcd.
However, this PR only includes a module with static pserver addresses. To be used for MPI cluster.
I will send a separate PR for the etcd module.

[dzhwinter]

get it

[dzhwinter]

maybe name with "param" better here?

[helinwang]

Thanks! Done.

[dzhwinter]

do we need to check the pserverNum == len(list) here to ensure that alive pserver instance equal the desired number?

[helinwang]

It's ok if number of pservers still did not reach the desired number. We will only connect to pservers that are alive. For pservers not alive yet, we will not connect to them, and all calls to them will be blocked until connected. (See: https://github.com/PaddlePaddle/Paddle/pull/2243/files#diff-b1a8f38187aa603e0efc16791f282d87R61)

[dzhwinter]

thanks for the explain. I got it. : )

[dzhwinter]

LGTM!