How to update the C++ sources of gRPC:

1. git clone http://github.com/grpc/grpc.git in a convenient directory
2. git checkout <tag> (current is release-0_13, commithash 78e04bbd)
3. mkdir -p third_party/grpc/src
4. cp -R <gRPC git tree>/src/{compiler,core-cpp} third_party/grpc/src
5. cp -R <gRPC git tree>/include third_party/grpc
6. Update BUILD files by copying the rules from the BUILD file of gRPC
7. Patch in grpc.patch. It makes gRPC work under msys2.

How to update the Java plugin:

1. Take version 0.15.0 from https://github.com/grpc/grpc-java commit hash is b7d816fb3d0d38e
2. cp -R <grpg-java git tree>/compiler/src/java_plugin third_party/grpc-java/compiler/src

How to update the Java code:

Download it from Maven central. The jars are called grpc-core, grpc-netty, grpc-protobuf, grpc-protobuf-lite, grpc-stub and the version is 0.15.0.