Harmony promises

src/promise.js

+// Copyright 2012 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+"use strict";
+
+// This file relies on the fact that the following declaration has been made
+// in runtime.js:
+// var $Object = global.Object
+// var $WeakMap = global.WeakMap
+
+
+var $Promise = Promise;
+
+
+//-------------------------------------------------------------------
+
+// Core functionality.
+
+// Event queue format: [(value, [(handler, deferred)*])*]
+// I.e., a list of value/tasks pairs, where the value is a resolution value or
+// rejection reason, and the tasks are a respective list of handler/deferred
+// pairs waiting for notification of this value. Each handler is an onResolve or
+// onReject function provided to the same call of 'when' that produced the
+// associated deferred.
+var promiseEvents = new InternalArray;
+
+// Status values: 0 = pending, +1 = resolved, -1 = rejected
+var promiseStatus = NEW_PRIVATE("Promise#status");
+var promiseValue = NEW_PRIVATE("Promise#value");
+var promiseOnResolve = NEW_PRIVATE("Promise#onResolve");
+var promiseOnReject = NEW_PRIVATE("Promise#onReject");
+var promiseRaw = NEW_PRIVATE("Promise#raw");
+
+function IsPromise(x) {
+  return IS_SPEC_OBJECT(x) && %HasLocalProperty(x, promiseStatus);
+}
+
+function Promise(resolver) {
+  if (resolver === promiseRaw) return;
+  var promise = PromiseInit(this);
+  resolver(function(x) { PromiseResolve(promise, x) },
+           function(r) { PromiseReject(promise, r) });
+}
+
+function PromiseSet(promise, status, value, onResolve, onReject) {
+  SET_PRIVATE(promise, promiseStatus, status);
+  SET_PRIVATE(promise, promiseValue, value);
+  SET_PRIVATE(promise, promiseOnResolve, onResolve);
+  SET_PRIVATE(promise, promiseOnReject, onReject);
+  return promise;
+}
+
+function PromiseInit(promise) {
+  return PromiseSet(promise, 0, UNDEFINED, new InternalArray, new InternalArray)
+}
+
+function PromiseDone(promise, status, value, promiseQueue) {
+  if (GET_PRIVATE(promise, promiseStatus) !== 0)
+    throw MakeTypeError('promise_not_pending', [promise]);
+  PromiseEnqueue(value, GET_PRIVATE(promise, promiseQueue));
+  PromiseSet(promise, status, value);
+}
+
+function PromiseResolve(promise, x) {
+  PromiseDone(promise, +1, x, promiseOnResolve)
+}
+
+function PromiseReject(promise, r) {
+  PromiseDone(promise, -1, r, promiseOnReject)
+}
+
+
+// Convenience.
+
+function PromiseDeferred() {
+  if (this === $Promise) {
+    // Optimized case, avoid extra closure.
+    var promise = PromiseInit(new Promise(promiseRaw));
+    return {
+      promise: promise,
+      resolve: function(x) { PromiseResolve(promise, x) },
+      reject: function(r) { PromiseReject(promise, r) }
+    };
+  } else {
+    var result = {};
+    result.promise = new this(function(resolve, reject) {
+      result.resolve = resolve;
+      result.reject = reject;
+    })
+    return result;
+  }
+}
+
+function PromiseResolved(x) {
+  if (this === $Promise) {
+    // Optimized case, avoid extra closure.
+    return PromiseSet(new Promise(promiseRaw), +1, x);
+  } else {
+    return new this(function(resolve, reject) { resolve(x) });
+  }
+}
+
+function PromiseRejected(r) {
+  if (this === $Promise) {
+    // Optimized case, avoid extra closure.
+    return PromiseSet(new Promise(promiseRaw), -1, r);
+  } else {
+    return new this(function(resolve, reject) { reject(r) });
+  }
+}
+
+
+// Simple chaining (a.k.a. flatMap).
+
+function PromiseNopHandler() {}
+
+function PromiseWhen(onResolve, onReject) {
+  onResolve = IS_UNDEFINED(onResolve) ? PromiseNopHandler : onResolve;
+  onReject = IS_UNDEFINED(onReject) ? PromiseNopHandler : onReject;
+  var deferred = %_CallFunction(this.constructor, PromiseDeferred);
+  switch (GET_PRIVATE(this, promiseStatus)) {
+    case UNDEFINED:
+      throw MakeTypeError('not_a_promise', [this]);
+    case 0:  // Pending
+      GET_PRIVATE(this, promiseOnResolve).push(onResolve, deferred);
+      GET_PRIVATE(this, promiseOnReject).push(onReject, deferred);
+      break;
+    case +1:  // Resolved
+      PromiseEnqueue(GET_PRIVATE(this, promiseValue), [onResolve, deferred]);
+      break;
+    case -1:  // Rejected
+      PromiseEnqueue(GET_PRIVATE(this, promiseValue), [onReject, deferred]);
+      break;
+  }
+  return deferred.promise;
+}
+
+function PromiseCatch(onReject) {
+  return this.when(UNDEFINED, onReject);
+}
+
+function PromiseEnqueue(value, tasks) {
+  promiseEvents.push(value, tasks);
+  %SetMicrotasksPending(true);
+}
+
+function PromiseMicrotasksRunner() {
+  var events = promiseEvents;
+  if (events.length > 0) {
+    promiseEvents = new InternalArray;
+    for (var i = 0; i < events.length; i += 2) {
+      var value = events[i];
+      var tasks = events[i + 1];
+      for (var j = 0; j < tasks.length; j += 2) {
+        var handler = tasks[j];
+        var deferred = tasks[j + 1];
+        try {
+          var result = handler(value);
+          if (result === deferred.promise)
+            throw MakeTypeError('promise_cyclic', [result]);
+          else if (IsPromise(result))
+            result.when(deferred.resolve, deferred.reject);
+          else
+            deferred.resolve(result);
+        } catch(e) {
+          try { deferred.reject(e) } catch(e) {}

[esprehn, 2013/11/15 11:23:19]

Swallowing exceptions like this is bad for developers, it should get logged to
the console or something.

[rossberg, 2013/11/15 12:56:57]

Good point, although we currently do the same for Object.observe observers. I'll
make that a TODO, as we still lack a good infrastructure for a better solution.

+        }
+      }
+    }
+  }
+}
+RunMicrotasks.runners.push(PromiseMicrotasksRunner);
+
+
+// Extended functionality for multi-unwrapping chaining and coercive 'then'.
+
+function PromiseThen(onResolve, onReject) {
+  onResolve = IS_UNDEFINED(onResolve) ? PromiseNopHandler : onResolve;
+  var that = this;
+  var constructor = this.constructor;
+  return this.when(
+    function(x) {
+      x = PromiseCoerce(constructor, x);
+      return x === that ? onReject(MakeTypeError('promise_cyclic', [x])) :
+             IsPromise(x) ? x.then(onResolve, onReject) : onResolve(x);
+    },
+    onReject
+  );
+}
+
+PromiseCoerce.table = new $WeakMap;
+
+function PromiseCoerce(constructor, x) {
+  if (IsPromise(x)) {
+    return x;
+  } else if (!IS_NULL_OR_UNDEFINED(x) && 'then' in TO_OBJECT_INLINE(x)) {
+    if (PromiseCoerce.table.has(x)) {
+      return PromiseCoerce.table.get(x);
+    } else {
+      var deferred = constructor.deferred();
+      PromiseCoerce.table.set(x, deferred.promise);
+      try {
+        x.then(deferred.resolve, deferred.reject);
+      } catch(e) {
+        deferred.reject(e);
+      }
+      return deferred.promise;
+    }
+  } else {
+    return x;
+  }
+}
+
+
+// Combinators.
+
+function PromiseCast(x) {
+  // TODO(rossberg): cannot do better until we support @@create.
+  return IsPromise(x) ? x : this.resolved(x);
+}
+
+function PromiseAll(values) {
+  var deferred = this.deferred();
+  var count = 0;
+  for (var i = 0; i < values.length; ++i) {
+    ++count;
+    this.cast(values[i]).when(
+      function(x) { if (--count === 0) deferred.resolve() },
+      function(r) { if (count > 0) { count = 0; deferred.reject(r) } }
+    );
+  }
+  return deferred.promise;
+}
+
+function PromiseOne(values) {
+  var deferred = this.deferred();
+  var done = false;
+  for (var i = 0; i < values.length; ++i) {
+    this.cast(values[i]).when(
+      function(x) { if (!done) { done = true; deferred.resolve(x) } },
+      function(r) { if (!done) { done = true; deferred.reject(r) } }
+    );
+  }
+  return deferred.promise;
+}
+
+//-------------------------------------------------------------------
+
+function SetUpPromise() {
+  %CheckIsBootstrapping()
+  global.Promise = $Promise;
+  InstallFunctions($Promise, DONT_ENUM, [
+    "deferred", PromiseDeferred,
+    "resolved", PromiseResolved,
+    "rejected", PromiseRejected,
+    "all", PromiseAll,
+    "one", PromiseOne,
+    "cast", PromiseCast
+  ]);
+  InstallFunctions($Promise.prototype, DONT_ENUM, [
+    "when", PromiseWhen,
+    "then", PromiseThen,
+    "catch", PromiseCatch
+  ]);
+}
+
+SetUpPromise();