Using spark-kernel comm API - api

Question

I started using spark-kernel recently.
As given in tutorial and sample code, I was able to set up client and use it for executing code snippets on spark-kernel and retrieving back results as given in this example code.
Now, I need to use comm API provided with spark-kernel. I tried this tutorial, but I am not able to make it work. In fact, I have no understanding of how to make that work.
I tried the following code, but when I run this code, I get this error "Received invalid target for Comm Open: my_target" on the kernel.
package examples
import scala.runtime.ScalaRunTime._
import scala.collection.mutable.ListBuffer
import com.ibm.spark.kernel.protocol.v5.MIMEType
import com.ibm.spark.kernel.protocol.v5.client.boot.ClientBootstrap
import com.ibm.spark.kernel.protocol.v5.client.boot.layers.{StandardHandlerInitialization, StandardSystemInitialization}
import com.ibm.spark.kernel.protocol.v5.content._
import com.typesafe.config.{Config, ConfigFactory}
import Array._
object commclient extends App{
val profileJSON: String = """
{
"stdin_port" : 48691,
"control_port" : 44808,
"hb_port" : 49691,
"shell_port" : 40544,
"iopub_port" : 43462,
"ip" : "127.0.0.1",
"transport" : "tcp",
"signature_scheme" : "hmac-sha256",
"key" : ""
}
""".stripMargin
val config: Config = ConfigFactory.parseString(profileJSON)
val client = (new ClientBootstrap(config)
with StandardSystemInitialization
with StandardHandlerInitialization).createClient()
def printResult(result: ExecuteResult) = {
println(s"${result.data.get(MIMEType.PlainText).get}")
}
def printStreamContent(content:StreamContent) = {
println(s"${content.text}")
}
def printError(reply:ExecuteReplyError) = {
println(s"Error was: ${reply.ename.get}")
}
client.comm.register("my_target").addMsgHandler {
(commWriter, commId, data) =>
println(data)
commWriter.close()
}
// Initiate the Comm connection
client.comm.open("my_target")
}
Can someone tell me how shall I run this piece of code:
// Register the callback to respond to being opened from the client
kernel.comm.register("my target").addOpenHandler {
(commWriter, commId, targetName, data) =>
commWriter.writeMsg(Map("response" -> "Hello World!"))
}
I would really appreciate if someone can point me to complete working example on usage of comm API.
Any help will be appreciated. Thanks

Answer 1

You can use your client to run this server (kernel) side registration once in one program. Then your other programs can communicate to kernel using this channel.
Here is a way I ran my registration in the first program I mentioned above:
client.execute(
"""
// Register the callback to respond to being opened from the client
kernel.comm.register("my target").
addOpenHandler {
(commWriter, commId, targetName, data) =>
commWriter.writeMsg(org.apache.toree.kernel.protocol.v5.MsgData("response" -> "Toree Hello World!"))
}.
addMsgHandler {
(commWriter, _, data) =>
if (!data.toString.contains("closing")) {
commWriter.writeMsg(data)
} else {
commWriter.writeMsg(org.apache.toree.kernel.protocol.v5.MsgData("closing" -> "done"))
}
}
""".stripMargin
)