-
Notifications
You must be signed in to change notification settings - Fork 22
/
suspend.js
340 lines (304 loc) · 9.61 KB
/
suspend.js
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
var Promise = require('promise/lib/es6-extensions');
/**
* Our suspend namespace, which doubles as an alias for `suspend.fn` (although
* at the code level it may be more accurate to say that `suspend.fn` is an
* alias for `suspend`...
* Accepts a generator and returns a new function that makes no assumptions
* regarding callback and/or error conventions.
*/
var suspend = module.exports = function fn(generator) {
if (!isGeneratorFunction(generator)) {
throw new Error('First .fn() argument must be a GeneratorFunction.');
}
return function() {
var suspender = new Suspender(generator);
// preserve `this` context
suspender.start(this, Array.prototype.slice.call(arguments));
};
};
suspend.fn = suspend;
/**
* Accepts a generator, and returns a new function that follows Node's callback
* conventions. The callback is required.
*/
suspend.callback = function callback(generator) {
if (!isGeneratorFunction(generator)) {
throw new Error('First .callback() argument must be a GeneratorFunction.');
}
return function() {
var callback = arguments[arguments.length - 1],
args = Array.prototype.slice.call(arguments, 0, -1);
if (typeof callback !== 'function') {
throw new Error('Last argument must be a callback function.');
}
var suspender = new Suspender(generator, callback);
// preserve `this` context
suspender.start(this, args);
};
};
/**
* Accepts a generator, and returns a new function that returns a promise.
*/
suspend.promise = function promise(generator) {
if (!isGeneratorFunction(generator)) {
throw new Error('First .promise() argument must be a GeneratorFunction.');
}
return function() {
var self = this,
args = Array.prototype.slice.call(arguments);
return new Promise(function(resolve, reject) {
var suspender = new Suspender(generator, function(err, ret) {
err ? reject(err) : resolve(ret);
});
suspender.start(self, args);
});
};
};
/**
* Accepts a generator and an optional callback. The generator is invoked
* immediately - any errors or returned values are passed to the callback.
*/
suspend.run = function run(generator, callback) {
if (!isGeneratorFunction(generator)) {
throw new Error('First .run() argument must be a GeneratorFunction.');
}
if (callback && typeof callback !== 'function') {
throw new Error('Second .run() argument must be a callback function.');
}
var suspender = new Suspender(generator, callback);
// preserve `this` context
suspender.start(this);
};
/**
* Factory method for creating node-style callbacks that know how to resume
* execution of the generator. The callback expects the first argument to be
* an error, if it occurred, or the completion value as the second argument.
*/
suspend.resume = function resumeFactory() {
var suspender = getActiveSuspender();
if (!suspender) {
throw new Error('resume() must be called from the generator body.');
}
var alreadyResumed = false;
return function resume() {
if (alreadyResumed) {
throw new Error('Cannot call same resumer multiple times.');
}
alreadyResumed = true;
suspender.resume.apply(suspender, arguments);
};
};
/**
* Factory method for creating a callback that doesn't make any assumptions
* regarding Node's callback conventions. All arguments passed to it are made
* available in an array.
*/
suspend.resumeRaw = function resumeRawFactory() {
var resume = suspend.resume.apply(this, arguments);
getActiveSuspender().rawResume = true;
return resume;
};
/**
* Used for "forking" parallel operations. Rather than resuming the generator,
* completion values are stored until a subsequent `.join()` operation.
*/
suspend.fork = function fork() {
var suspender = getActiveSuspender();
if (!suspender) {
throw new Error('fork() must be called from the generator body.');
}
return suspender.forkFactory();
};
/**
* Similar to `resume()`, except that the resulting value is an array of all
* the completion values from previous `fork()` operations.
*/
suspend.join = function join() {
var suspender = getActiveSuspender();
if (!suspender) {
throw new Error('join() must be called from the generator body.');
}
if (suspender.pendingJoin) {
throw new Error('There is already a join() pending unresolved forks.');
}
suspender.join();
};
/**
* Constructor function used for "wrapping" generator. Manages the state and
* interactions with a suspend-wrapped generator.
*/
function Suspender(generator, callback) {
var self = this;
this.generator = generator;
// initialized in start()
this.iterator = null;
// flag to keep track of whether or not the entire generator completed.
// See start() for state tracking.
this.syncComplete = true;
// makes sure to not unleash zalgo: https://github.com/jmar777/suspend/pull/21
this.callback = callback && function() {
if (self.syncComplete) {
var args = Array.prototype.slice.call(arguments);
setImmediate(function() {
callback.apply(this, args);
});
} else {
callback.apply(this, arguments);
}
};
// flag indicating whether or not the iterator has completed
this.done = false;
// flag to keep track of whether or not we were resumed synchronously.
// See nextOrThrow() for state tracking.
this.syncResume = false;
// flag indicating whether or not the values passed to resume() should be
// treated as raw values, or handled per the error-first callback convention
this.rawResume = false;
// holding place for values from forked operations, waiting for a join()
this.forkValues = [];
// number of pending forks we have out there
this.pendingForks = 0;
// index used for preserving fork result positions
this.forkIndex = 0;
// flag indicating whether or not we have a pending join operation (which
// waits until all forks are resolved)
this.pendingJoin = false;
}
/**
* Starts the generator and begins iteration.
*/
Suspender.prototype.start = function start(ctx, args) {
this.iterator = this.generator.apply(ctx, args);
this.nextOrThrow();
this.syncComplete = false;
};
/**
* Handles values that are yielded from the generator (such as promises).
*/
Suspender.prototype.handleYield = function handleYield(ret) {
if (ret.done) {
this.done = true;
if (this.callback) {
this.callback.call(null, null, ret.value);
}
return;
}
// if nothing was yielded, then assume that resume()/join() are being used
if (!ret.value) return;
// check if a promise was yielded
if (typeof ret.value.then === 'function') {
// todo: may be more efficient to have a single instance-level resume
// function
ret.value.then(this.resume.bind(this, null), this.resume.bind(this));
}
};
/**
* Calls `.next()` or `.throw()` on the iterator, depending on the value of the
* `isError` flag. This method ensures that yielded values and thrown errors
* will be properly handled, and helps keep track of whether or not we are
* resumed synchronously.
*/
Suspender.prototype.nextOrThrow = function next(val, isError) {
var self = this;
this.syncResume = true;
setActiveSuspender(this);
var ret;
try {
ret = isError ? this.iterator.throw(val) : this.iterator.next(val);
} catch (err) {
// prevents promise swallowing: https://github.com/jmar777/suspend/pull/21
setImmediate(function() {
if (self.callback) {
return self.callback(err);
} else {
throw err;
}
});
return;
} finally {
this.syncResume = false;
clearActiveSuspender();
}
// everything was ok, so keep going
this.handleYield(ret);
};
/**
* Resumes execution of the generator once an async operation has completed.
*/
Suspender.prototype.resume = function resume(err, result) {
// if we have been synchronously resumed, then wait for the next turn on
// the event loop (avoids 'Generator already running' errors).
if (this.syncResume) {
return setImmediate(this.resume.bind(this, err, result));
}
if (this.rawResume) {
this.rawResume = false;
this.nextOrThrow(Array.prototype.slice.call(arguments));
} else {
if (this.done) {
throw new Error('Generators cannot be resumed once completed.');
}
if (err) return this.nextOrThrow(err, true);
this.nextOrThrow(result);
}
};
/**
* Returns a fork continuation that stashes the fulfillment value until `join()`
* is subsequently called.
*/
Suspender.prototype.forkFactory = function forkFactory() {
var self = this,
index = this.forkIndex++,
alreadyFulfilled = false;
this.pendingForks++;
return function fork() {
if (alreadyFulfilled) {
throw new Error('fork was fulfilled more than once.');
}
alreadyFulfilled = true;
self.forkValues[index] = Array.prototype.slice.call(arguments);
if (--self.pendingForks === 0 && self.pendingJoin) {
self.join();
}
};
};
/**
* Causes the generator to be resumed (with the values of any previous `fork()`
* fulfillments).
*/
Suspender.prototype.join = function join() {
this.pendingJoin || (this.pendingJoin = true);
if (this.pendingForks) return;
var err = null,
results = [];
for (var i = 0, len = this.forkValues.length; i < len; i++) {
var forkValue = this.forkValues[i];
if (forkValue[0]) {
err = forkValue[0];
break;
} else {
results[i] = forkValue[1];
}
}
// reset fork/join state
this.pendingJoin = false;
this.pendingForks = 0;
this.forkIndex = 0;
this.forkValues.length = 0;
// resume the generator with our fork/join results
this.resume(err, results);
};
// keep track of the currently active generator (used by the resumer factory).
var suspenderStack = [];
function setActiveSuspender(suspender) {
suspenderStack.push(suspender);
}
function getActiveSuspender() {
return suspenderStack[suspenderStack.length - 1];
}
function clearActiveSuspender() {
suspenderStack.pop();
}
function isGeneratorFunction(v) {
return v && v.constructor && v.constructor.name === 'GeneratorFunction';
}