isolates: drain message queue completely

src/node_isolate.cc

@@ -87,17 +87,23 @@ public:
     uv_mutex_unlock(&mutex_);
   }
 
-  T Consume() {
+  bool Consume(T& item) {
+    ngx_queue_t* q = NULL;
+
     uv_mutex_lock(&mutex_);
-    ngx_queue_t* q = ngx_queue_head(&queue_);
+    if (!ngx_queue_empty(&queue_)) {
+      q = ngx_queue_head(&queue_);
       ngx_queue_remove(q);
+    }
     uv_mutex_unlock(&mutex_);
 
+    if (q == NULL) return false;
+
     Message* m = ngx_queue_data(q, Message, queue_);
-    T item = m->item_;
+    item = m->item_;
     delete m;
 
-    return item;
+    return true;
   }
 
 private:
@@ -140,8 +146,8 @@ private:
   }
 
   void OnMessage() {
-    T item = queue_.Consume();
-    callback_(item, arg_);
+    T item;
+    while (queue_.Consume(item)) callback_(item, arg_);
   }
 
   void* arg_;

test/simple/test-isolates-ping-pong.js

@@ -1,6 +1,11 @@
 var isolates = process.binding('isolates');
+var assert = require('assert');
 
-var N = 4; // # of child isolates
+var N_ISOLATES = 4;
+var N_MESSAGES = 20;
+var N_MESSAGES_PER_TICK = 4;
+
+assert(N_MESSAGES % N_MESSAGES_PER_TICK == 0);
 
 if (process.tid === 1)
   master();
@@ -8,32 +13,56 @@ else
   child();
 
 function master() {
-  for (var i = 0; i < N; ++i) spawn();
+  for (var i = 0; i < N_ISOLATES; ++i) spawn();
 
   function spawn() {
     var isolate = isolates.create(process.argv);
+
+    var gotExit = false; // exit event emitted?
+    var msgId = 0; // message IDs seen so far
+    var tick = 0;
+
     isolate.onexit = function() {
-      console.error("onexit isolate #%d", isolate.tid);
+      gotExit = true;
     };
-    isolate.onmessage = function(m) {
-      console.error("parent received message '%s'", m);
-      isolate.send(Buffer('ACK ' + m));
+
+    isolate.onmessage = function(buf) {
+      var msg = JSON.parse(buf);
+      assert.equal(msg.id, msgId + 1); // verify that messages arrive in order
+      assert.equal(msg.tick, tick); // and on the proper tick (=full mq drain)
+      msgId = msg.id;
+      if (msgId % N_MESSAGES_PER_TICK == 0) tick++;
+      isolate.send(buf);
     };
+
+    process.on('exit', function() {
+      assert.equal(gotExit, true);
+      assert.equal(msgId, N_MESSAGES);
+      assert.equal(tick, N_MESSAGES / N_MESSAGES_PER_TICK);
+    });
   }
 }
 
 function child() {
-  var n = 0;
+  var msgId = 0;
+  var tick = 0;
 
   function send() {
-    if (++n > 10) return;
-    process._send(Buffer('SYN' + n));
+    // Send multiple messages, verify that the message queue
+    // is completely drained on each tick of the event loop.
+    for (var i = 0; i < N_MESSAGES_PER_TICK; ++i) {
+      process.send({tick:tick, id:++msgId});
+    }
+
+    if (msgId < N_MESSAGES) {
       setTimeout(send, 10);
     }
 
+    tick++;
+  }
+
   send();
 
   process._onmessage = function(m) {
-    console.error("child %d received message '%s'", process.tid, m);
   };
 }