Update testground example

testground/simple_tcp_ping/main.nim

@@ -1,8 +1,21 @@
-import std/strutils, testground_sdk, chronos, stew/byteutils
+import std/strutils, std/random
+import testground_sdk, chronos, stew/byteutils
+
+type
+  AwesomeStruct = object
+    rand: int
 
 testground(client):
   let
+    # signalAndWait is a shortcut for
+    # x = await client.signal("setup")
+    # await client.waitForBarrier("setup", client.testInstanceCount)
+    # In this case, it will signal that we are at the "setup" stage,
+    # and wait for "testInstanceCount" (so every instance) to reach this stage.
+    #
+    # signal will also return the number of nodes that reached this stage before us
     myId = await client.signalAndWait("setup", client.testInstanceCount)
+    # here we are using this id to generate our local ip
     myIp = client.testSubnet.split('.')[0..1].join(".") & ".1." & $myId
     serverIp = client.testSubnet.split('.')[0..1].join(".") & ".1.1"
   await client.updateNetworkParameter(
@@ -10,28 +23,42 @@ testground(client):
       network: "default",
       ipv4: some myIp & "/24",
       enable: true,
+      # signal this state once the network parameters are applied
       callback_state: "network_setup",
       callback_target: some client.testInstanceCount,
       routing_policy: "accept_all",
     )
   )
 
+  # wait for everyone to reach the state with proper networking setup
   await client.waitForBarrier("network_setup", client.testInstanceCount)
 
+  # useless pubsub demo
+  randomize()
+  await client.publish("rands", AwesomeStruct(rand: rand(100)))
+  let randomValues = client.subscribe("rands", AwesomeStruct)
+  for _ in 0 ..< 2:
+    echo await randomValues.popFirst()
+
+  # read parameters from the composition or command line flags
   let
     payload = client.param(string, "payload")
     count = client.param(int, "count")
     printResult = client.param(bool, "printResult")
+
   if myId == 1: # server
-    let
-      server = createStreamServer(initTAddress(myIp & ":5050"), flags = {ReuseAddr})
-      connection = await server.accept()
+    let server = createStreamServer(initTAddress(myIp & ":5050"), flags = {ReuseAddr})
+    # We are ready for clients
+    discard await client.signalAndWait("ready", client.testInstanceCount)
+    let connection = await server.accept()
 
     for _ in 0 ..< count:
       doAssert (await connection.write(payload.toBytes())) == payload.len
     connection.close()
 
   else: # client
+    # wait for the server to be started
+    discard await client.signalAndWait("ready", client.testInstanceCount)
     let connection = await connect(initTAddress(serverIp & ":5050"))
     var buffer = newSeq[byte](payload.len)