Fix the nextTick(cb) causing event loop starvation

If you run more than 1000 lookups (like processing a big directory of
files), you will get lots of warnings from node.  Solution is to use
setImmediate(cb) instead.

lib/executor.js

@@ -22,7 +22,11 @@ function Executor () {
     // Always tell the queue task is complete. Execute callback if any was given.
     if (typeof lastArg === 'function') {
       callback = function () {
+        if (typeof setImmediate === 'function') {
+           setImmediate(cb);
+        } else {
           process.nextTick(cb);
+        }
         lastArg.apply(null, arguments);
       };
 

test/executor.test.js

@@ -76,6 +76,21 @@ function testRightOrder (d, done) {
   
 
 
+// Note:  The following test does not have any assertion because it
+// is meant to address the deprecation warning:
+// (node) warning: Recursive process.nextTick detected. This will break in the next version of node. Please use setImmediate for recursive deferral.
+// see
+var testEventLoopStarvation = function(d, done){
+   var times = 1001;
+   var i = 0;
+   while ( i <times) {
+      i++;
+     d.find({"bogus": "search"}, function (err, docs) {
+     });
+   }
+   done();
+ };
+
 describe('Executor', function () {
 
   describe('With persistent database', function () {
@@ -114,6 +129,10 @@ describe('Executor', function () {
       testRightOrder(d, done);
     });
 
+    it('Does not starve event loop and raise warning when more than 1000 callbacks are in queue', function(done){
+      testEventLoopStarvation(d, done);
+    });
+  
   });   // ==== End of 'With persistent database' ====