test: improve test-child-process-fork-dgram

Previous implementation was subject to timing out as there
was no guarantee that the parent or child would ever
receive a message.  Modified test so that once parent or
child receives a message it closes its connection to the
socket so we can guarantee the next messsage will be recieved
by the other node.

The test also left lingering processes when it timed out
so pulled the timeout into the test itself so that it
could properly cleanup in case of failure.

test/parallel/parallel.status

@@ -32,6 +32,3 @@ test-fs-watch-encoding               : FAIL, PASS
 
 #being worked under https://github.com/nodejs/node/issues/7973
 test-stdio-closed                        : PASS, FLAKY
-
-#covered by https://github.com/nodejs/node/issues/8271
-test-child-process-fork-dgram            : PASS, FLAKY

test/parallel/test-child-process-fork-dgram.js

@@ -8,9 +8,9 @@
  * Because it's not really possible to predict how the messages will be
  * distributed among the parent and the child processes, we keep sending
  * messages until both the parent and the child received at least one
- * message. The worst case scenario is when either one never receives
- * a message. In this case the test runner will timeout after 60 secs
- * and the test will fail.
+ * message. When either the parent or child receives a message we close
+ * the server on that side so the next message is guaranteed to be
+ * received by the other.
  */
 
 const common = require('../common');
@@ -26,22 +26,30 @@ if (common.isWindows) {
 
 var server;
 if (process.argv[2] === 'child') {
+  var serverClosed = false;
   process.on('message', function removeMe(msg, clusterServer) {
     if (msg === 'server') {
       server = clusterServer;
 
       server.on('message', function() {
         process.send('gotMessage');
+        // got a message so close the server to make sure
+        // the parent also gets a message
+        serverClosed = true;
+        server.close();
       });
 
     } else if (msg === 'stop') {
-      server.close();
       process.removeListener('message', removeMe);
+      if (!serverClosed) {
+        server.close();
+      }
     }
   });
 
 } else {
   server = dgram.createSocket('udp4');
+  var serverPort = null;
   var client = dgram.createSocket('udp4');
   var child = fork(__filename, ['child']);
 
@@ -52,9 +60,13 @@ if (process.argv[2] === 'child') {
 
   server.on('message', function(msg, rinfo) {
     parentGotMessage = true;
+    // got a message so close the server to make sure
+    // the child also gets a message
+    server.close();
   });
 
   server.on('listening', function() {
+    serverPort = server.address().port;
     child.send('server', server);
 
     child.once('message', function(msg) {
@@ -66,13 +78,16 @@ if (process.argv[2] === 'child') {
     sendMessages();
   });
 
+  var iterations = 0;
   var sendMessages = function() {
     var timer = setInterval(function() {
+      iterations++;
+
       client.send(
         msg,
         0,
         msg.length,
-        server.address().port,
+        serverPort,
         '127.0.0.1',
         function(err) {
           if (err) throw err;
@@ -83,7 +98,8 @@ if (process.argv[2] === 'child') {
        * Both the parent and the child got at least one message,
        * test passed, clean up everyting.
        */
-      if (parentGotMessage && childGotMessage) {
+      if ((parentGotMessage && childGotMessage) ||
+          ((iterations / 1000) > 45)) {
         clearInterval(timer);
         shutdown();
       }
@@ -94,7 +110,9 @@ if (process.argv[2] === 'child') {
   var shutdown = function() {
     child.send('stop');
 
-    server.close();
+    if (!parentGotMessage) {
+      server.close();
+    }
     client.close();
   };