Avoid recursion during tail calls.

An asynchronous task that finishes would previously trigger recursive invocation
of subsequent synchronous tasks. Now these tasks are handled in a loop instead.

Makefile

@@ -1,7 +1,3 @@
-NODE_PATH ?= ./node_modules
-JS_COMPILER = $(NODE_PATH)/uglify-js/bin/uglifyjs
-JS_TESTER = $(NODE_PATH)/vows/bin/vows
-
 all: \
 	queue.min.js \
 	component.json \
@@ -18,11 +14,12 @@ package.json: src/package.js queue.js
 	@chmod a-w $@
 
 test: all
-	@$(JS_TESTER)
+	node_modules/.bin/vows
+	@echo
 
 %.min.js: %.js Makefile
 	@rm -f $@
-	$(JS_COMPILER) < $< > $@
+	node_modules/.bin/uglifyjs $< -c -m -o $@
 
 clean:
 	rm -f queue.min.js component.json package.json

component.json

@@ -1,5 +1,5 @@
 {
   "name": "queue-async",
-  "version": "1.0.1",
+  "version": "1.0.2",
   "main": "./queue.js"
 }

package.json

@@ -1,6 +1,6 @@
 {
   "name": "queue-async",
-  "version": "1.0.1",
+  "version": "1.0.2",
   "description": "A little helper for asynchronous JavaScript.",
   "keywords": [
     "asynchronous",
@@ -13,14 +13,14 @@
   },
   "repository": {
     "type": "git",
-    "url": "http://github.com/mbostock/queue.git"
+    "url": "https://github.com/mbostock/queue.git"
   },
   "main": "queue.js",
   "devDependencies": {
-    "uglify-js": "2.2.3",
-    "vows": "0.7.0"
+    "uglify-js": "~2.2.5",
+    "vows": "~0.7.0"
   },
   "scripts": {
-    "test": "./node_modules/vows/bin/vows"
+    "test": "node_modules/.bin/vows"
   }
 }

queue.js

@@ -1,8 +1,9 @@
 (function() {
   if (typeof module === "undefined") self.queue = queue;
   else module.exports = queue;
+  queue.version = "1.0.2";
 
-  queue.version = "1.0.1";
+  var slice = [].slice;
 
   function queue(parallelism) {
     var queue = {},
@@ -14,13 +15,13 @@
         await = noop,
         awaitAll;
 
-    if (arguments.length < 1) parallelism = Infinity;
+    if (!parallelism) parallelism = Infinity;
 
     queue.defer = function() {
       if (!error) {
         var node = arguments;
-        node.index = results.push(undefined) - 1;
-        if (tail) tail.next = node, tail = tail.next;
+        node.i = results.push(undefined) - 1;
+        if (tail) tail._ = node, tail = tail._;
         else head = tail = node;
         ++remaining;
         pop();
@@ -43,13 +44,14 @@
     };
 
     function pop() {
-      if (head && active < parallelism) {
+      var popping;
+      while (popping = head && active < parallelism) {
         var node = head,
             f = node[0],
-            a = Array.prototype.slice.call(node, 1),
-            i = node.index;
+            a = slice.call(node, 1),
+            i = node.i;
         if (head === tail) head = tail = null;
-        else head = head.next;
+        else head = head._;
         ++active;
         a.push(function(e, r) {
           --active;
@@ -63,7 +65,7 @@
             notify();
           } else {
             results[i] = r;
-            if (--remaining) pop();
+            if (--remaining) popping || pop();
             else notify();
           }
         });

src/package.js

@@ -15,14 +15,14 @@ console.log(JSON.stringify({
   },
   "repository": {
     "type": "git",
-    "url": "http://github.com/mbostock/queue.git"
+    "url": "https://github.com/mbostock/queue.git"
   },
   "main": "queue.js",
   "devDependencies": {
-    "uglify-js": "2.2.3",
-    "vows": "0.7.0"
+    "uglify-js": "~2.2.5",
+    "vows": "~0.7.0"
   },
   "scripts": {
-    "test": "./node_modules/vows/bin/vows"
+    "test": "node_modules/.bin/vows"
   }
 }, null, 2));

test/queue-test.js

@@ -188,10 +188,10 @@ suite.addBatch({
     }
   },
 
-  "fully-parallel queue of ten synchronous tasks": {
+  "serialized queue of ten deferred synchronous tasks": {
     topic: function() {
-      var t = synchronousTask();
-      queue()
+      var t = deferredSynchronousTask();
+      queue(1)
           .defer(t)
           .defer(t)
           .defer(t)
@@ -203,12 +203,13 @@ suite.addBatch({
           .defer(t)
           .defer(t)
           .awaitAll(this.callback);
+      t.finish();
     },
     "does not fail": function(error, results) {
       assert.isNull(error);
     },
-    "executes all tasks in series": function(error, results) {
-      assert.deepEqual(results, [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]);
+    "executes all tasks in series, within the callback of the first task": function(error, results) {
+      assert.deepEqual(results, [1, 2, 2, 2, 2, 2, 2, 2, 2, 2]);
     }
   },
 
@@ -288,3 +289,31 @@ function synchronousTask() {
     }
   };
 }
+
+function deferredSynchronousTask() {
+  var active = 0,
+      callbacks = [];
+
+  function task(callback) {
+    if (callbacks) return callbacks.push(callback);
+    try {
+      callback(null, ++active);
+    } finally {
+      --active;
+    }
+  }
+
+  task.finish = function() {
+    var callbacks_ = callbacks.slice();
+    callbacks = null;
+    callbacks_.forEach(function(callback) {
+      try {
+        callback(null, ++active);
+      } finally {
+        --active;
+      }
+    });
+  };
+
+  return task;
+}