ensureAsync

README.md

@@ -174,6 +174,7 @@ Usage:
 
 * [`memoize`](#memoize)
 * [`unmemoize`](#unmemoize)
+* [`ensureAsync`](#ensureAsync)
 * [`log`](#log)
 * [`dir`](#dir)
 * [`noConflict`](#noConflict)
@@ -1657,6 +1658,41 @@ __Arguments__
 
 * `fn` - the memoized function
 
+---------------------------------------
+
+<a name="ensureAsync" />
+### ensureAsync(fn)
+
+Wrap an async function and ensure it calls its callback on a later tick of the event loop.  If the function already calls its callback on a next tick, no extra deferral is added. This is useful for preventing stack overflows (`RangeError: Maximum call stack size exceeded`) and generally keeping [Zalgo](http://blog.izs.me/post/59142742143/designing-apis-for-asynchrony) contained.
+
+__Arguments__
+
+* `fn` - an async function, one that expects a node-style callback as its last argument
+
+Returns a wrapped function with the exact same call signature as the function passed in.
+
+__Example__
+
+```js
+function sometimesAsync(arg, callback) {
+  if (cache[arg]) {
+    return callback(null, cache[arg]); // this would be synchronous!!
+  } else {
+    doSomeIO(arg, callback); // this IO would be asynchronous
+  }
+}
+
+// this has a risk of stack overflows if many results are cached in a row
+async.mapSeries(args, sometimesAsync, done); 
+
+// this will defer sometimesAsync's callback if necessary, 
+// preventing stack overflows
+async.mapSeries(args, async.ensureAsync(sometimesAsync), done);
+
+```
+
+---------------------------------------
+
 <a name="log" />
 ### log(function, arguments)
 

lib/async.js

@@ -1255,18 +1255,39 @@
     async.applyEachSeries = doSeries(_applyEach);
 
     async.forever = function (fn, callback) {
+        var done = only_once(callback || noop);
+        var task = ensureAsync(fn);
         function next(err) {
             if (err) {
-                if (callback) {
-                    return callback(err);
-                }
-                throw err;
+                return done(err);
             }
-            fn(next);
+            task(next);
         }
         next();
     };
 
+    function ensureAsync(fn) {
+        return function (/*...args, callback*/) {
+            var args = _baseSlice(arguments);
+            var callback = args.pop();
+            args.push(function () {
+                var innerArgs = arguments;
+                if (sync) {
+                    async.setImmediate(function () {
+                        callback.apply(null, innerArgs);
+                    });
+                } else {
+                    callback.apply(null, innerArgs);
+                }
+            });
+            var sync = true;
+            fn.apply(this, args);
+            sync = false;
+        };
+    }
+
+    async.ensureAsync = ensureAsync;
+
     // Node.js
     if (typeof module !== 'undefined' && module.exports) {
         module.exports = async;

perf/benchmark.js

@@ -2,7 +2,6 @@
 
 var _ = require("lodash");
 var Benchmark = require("benchmark");
-var benchOptions = {defer: true, minSamples: 1, maxTime: 2};
 var exec = require("child_process").exec;
 var fs = require("fs");
 var path = require("path");
@@ -16,8 +15,11 @@ var args = require("yargs")
   .alias("g", "grep")
   .default("g", ".*")
   .describe("i", "skip benchmarks whose names match this regex")
-  .alias("g", "reject")
+  .alias("i", "reject")
   .default("i", "^$")
+  .describe("l", "maximum running time per test (in seconds)")
+  .alias("l", "limit")
+  .default("l", 2)
   .help('h')
   .alias('h', 'help')
   .example('$0 0.9.2 0.9.0', 'Compare v0.9.2 with v0.9.0')
@@ -33,6 +35,7 @@ var reject = new RegExp(args.i, "i");
 var version0 = args._[0] || require("../package.json").version;
 var version1 = args._[1] || "current";
 var versionNames = [version0, version1];
+var benchOptions = {defer: true, minSamples: 1, maxTime: +args.l};
 var versions;
 var wins = {};
 var totalTime = {};
@@ -120,16 +123,30 @@ function doesNotMatch(suiteConfig) {
 function createSuite(suiteConfig) {
   var suite = new Benchmark.Suite();
   var args = suiteConfig.args;
+  var errored = false;
 
   function addBench(version, versionName) {
     var name = suiteConfig.name + " " + versionName;
+
+    try {
+      suiteConfig.setup(1);
+      suiteConfig.fn(version, function () {});
+    } catch (e) {
+      console.error(name + " Errored");
+      errored = true;
+      return;
+    }
+
     suite.add(name, function (deferred) {
       suiteConfig.fn(version, function () {
         deferred.resolve();
       });
     }, _.extend({
       versionName: versionName,
-      setup: _.partial.apply(null, [suiteConfig.setup].concat(args))
+      setup: _.partial.apply(null, [suiteConfig.setup].concat(args)),
+      onError: function (err) {
+        console.log(err.stack);
+      }
     }, benchOptions));
   }
 
@@ -139,18 +156,22 @@ function createSuite(suiteConfig) {
 
   return suite.on('cycle', function(event) {
     var mean = event.target.stats.mean * 1000;
-    console.log(event.target + ", " + (+mean.toPrecision(2)) + "ms per run");
+    console.log(event.target + ", " + (+mean.toPrecision(3)) + "ms per run");
     var version = event.target.options.versionName;
+    if (errored) return;
     totalTime[version] += mean;
   })
+  .on('error', function (err) { console.error(err); })
   .on('complete', function() {
-    var fastest = this.filter('fastest');
-    if (fastest.length === 2) {
-      console.log("Tie");
-    } else {
-      var winner = fastest[0].options.versionName;
-      console.log(winner + ' is faster');
-      wins[winner]++;
+    if (!errored) {
+      var fastest = this.filter('fastest');
+      if (fastest.length === 2) {
+        console.log("Tie");
+      } else {
+        var winner = fastest[0].options.versionName;
+        console.log(winner + ' is faster');
+        wins[winner]++;
+      }
     }
     console.log("--------------------------------------");
   });

perf/suites.js

@@ -204,6 +204,30 @@ module.exports = [
     fn: function (async, done) {
       setTimeout(done, 0);
     }
+  },
+  {
+    name: "ensureAsync sync",
+    fn: function (async, done) {
+      async.ensureAsync(function (cb) {
+        cb();
+      })(done);
+    }
+  },
+  {
+    name: "ensureAsync async",
+    fn: function (async, done) {
+      async.ensureAsync(function (cb) {
+        setImmediate(cb);
+      })(done);
+    }
+  },
+  {
+    name: "ensureAsync async noWrap",
+    fn: function (async, done) {
+      (function (cb) {
+        setImmediate(cb);
+      }(done));
+    }
   }
 ];
 

test/test-async.js

@@ -80,8 +80,10 @@ function getFunctionsObject(call_order) {
     };
 }
 
-exports['forever'] = function (test) {
-    test.expect(1);
+exports['forever'] = {
+
+'async': function (test) {
+    test.expect(2);
     var counter = 0;
     function addOne(callback) {
         counter++;
@@ -94,8 +96,28 @@ exports['forever'] = function (test) {
     }
     async.forever(addOne, function (err) {
         test.equal(err, 'too big!');
+        test.equal(counter, 50);
+        test.done();
+    });
+},
+
+'sync': function (test) {
+    test.expect(2);
+    var counter = 0;
+    function addOne(callback) {
+        counter++;
+        if (counter === 50000) {
+            return callback('too big!');
+        }
+        callback();
+    }
+    async.forever(addOne, function (err) {
+        test.equal(err, 'too big!');
+        test.equal(counter, 50000);
         test.done();
     });
+}
+
 };
 
 exports['applyEach'] = function (test) {
@@ -1030,12 +1052,12 @@ exports['parallel does not continue replenishing after error'] = function (test)
         }
         setTimeout(function(){
             callback();
-        }, delay); 
+        }, delay);
     }
 
     async.parallelLimit(arr, limit, function(x, callback) {
 
-    }, function(err){}); 
+    }, function(err){});
 
     setTimeout(function(){
         test.equal(started, 3);
@@ -1438,7 +1460,7 @@ exports['eachLimit does not continue replenishing after error'] = function (test
         setTimeout(function(){
             callback();
         }, delay);
-    }, function(err){}); 
+    }, function(err){});
 
     setTimeout(function(){
         test.equal(started, 3);
@@ -1743,7 +1765,7 @@ exports['mapLimit does not continue replenishing after error'] = function (test)
         setTimeout(function(){
             callback();
         }, delay);
-    }, function(err){}); 
+    }, function(err){});
 
     setTimeout(function(){
         test.equal(started, 3);
@@ -3561,3 +3583,55 @@ exports['queue started'] = function(test) {
 
 };
 
+exports['ensureAsync'] = {
+    'defer sync functions': function (test) {
+        var sync = true;
+        async.ensureAsync(function (arg1, arg2, cb) {
+            test.equal(arg1, 1);
+            test.equal(arg2, 2);
+            cb(null, 4, 5);
+        })(1, 2, function (err, arg4, arg5) {
+            test.equal(err, null);
+            test.equal(arg4, 4);
+            test.equal(arg5, 5);
+            test.ok(!sync, 'callback called on same tick');
+            test.done();
+        });
+        sync = false;
+    },
+
+    'do not defer async functions': function (test) {
+        var sync = false;
+        async.ensureAsync(function (arg1, arg2, cb) {
+            test.equal(arg1, 1);
+            test.equal(arg2, 2);
+            async.setImmediate(function () {
+                sync = true;
+                cb(null, 4, 5);
+                sync = false;
+            });
+        })(1, 2, function (err, arg4, arg5) {
+            test.equal(err, null);
+            test.equal(arg4, 4);
+            test.equal(arg5, 5);
+            test.ok(sync, 'callback called on next tick');
+            test.done();
+        });
+    },
+
+    'double wrapping': function (test) {
+        var sync = true;
+        async.ensureAsync(async.ensureAsync(function (arg1, arg2, cb) {
+            test.equal(arg1, 1);
+            test.equal(arg2, 2);
+            cb(null, 4, 5);
+        }))(1, 2, function (err, arg4, arg5) {
+            test.equal(err, null);
+            test.equal(arg4, 4);
+            test.equal(arg5, 5);
+            test.ok(!sync, 'callback called on same tick');
+            test.done();
+        });
+        sync = false;
+    }
+};