зеркало из https://github.com/mozilla/gecko-dev.git
528 строки
17 KiB
JavaScript
528 строки
17 KiB
JavaScript
/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
|
|
/* vim: set ts=2 et sw=2 tw=80 filetype=javascript: */
|
|
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
|
|
* You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
"use strict";
|
|
|
|
this.EXPORTED_SYMBOLS = [
|
|
"Task"
|
|
];
|
|
|
|
/**
|
|
* This module implements a subset of "Task.js" <http://taskjs.org/>.
|
|
*
|
|
* Paraphrasing from the Task.js site, tasks make sequential, asynchronous
|
|
* operations simple, using the power of JavaScript's "yield" operator.
|
|
*
|
|
* Tasks are built upon generator functions and promises, documented here:
|
|
*
|
|
* <https://developer.mozilla.org/en/JavaScript/Guide/Iterators_and_Generators>
|
|
* <http://wiki.commonjs.org/wiki/Promises/A>
|
|
*
|
|
* The "Task.spawn" function takes a generator function and starts running it as
|
|
* a task. Every time the task yields a promise, it waits until the promise is
|
|
* fulfilled. "Task.spawn" returns a promise that is resolved when the task
|
|
* completes successfully, or is rejected if an exception occurs.
|
|
*
|
|
* -----------------------------------------------------------------------------
|
|
*
|
|
* Cu.import("resource://gre/modules/Task.jsm");
|
|
*
|
|
* Task.spawn(function* () {
|
|
*
|
|
* // This is our task. Let's create a promise object, wait on it and capture
|
|
* // its resolution value.
|
|
* let myPromise = getPromiseResolvedOnTimeoutWithValue(1000, "Value");
|
|
* let result = yield myPromise;
|
|
*
|
|
* // This part is executed only after the promise above is fulfilled (after
|
|
* // one second, in this imaginary example). We can easily loop while
|
|
* // calling asynchronous functions, and wait multiple times.
|
|
* for (let i = 0; i < 3; i++) {
|
|
* result += yield getPromiseResolvedOnTimeoutWithValue(50, "!");
|
|
* }
|
|
*
|
|
* return "Resolution result for the task: " + result;
|
|
* }).then(function (result) {
|
|
*
|
|
* // result == "Resolution result for the task: Value!!!"
|
|
*
|
|
* // The result is undefined if no value was returned.
|
|
*
|
|
* }, function (exception) {
|
|
*
|
|
* // Failure! We can inspect or report the exception.
|
|
*
|
|
* });
|
|
*
|
|
* -----------------------------------------------------------------------------
|
|
*
|
|
* This module implements only the "Task.js" interfaces described above, with no
|
|
* additional features to control the task externally, or do custom scheduling.
|
|
* It also provides the following extensions that simplify task usage in the
|
|
* most common cases:
|
|
*
|
|
* - The "Task.spawn" function also accepts an iterator returned by a generator
|
|
* function, in addition to a generator function. This way, you can call into
|
|
* the generator function with the parameters you want, and with "this" bound
|
|
* to the correct value. Also, "this" is never bound to the task object when
|
|
* "Task.spawn" calls the generator function.
|
|
*
|
|
* - In addition to a promise object, a task can yield the iterator returned by
|
|
* a generator function. The iterator is turned into a task automatically.
|
|
* This reduces the syntax overhead of calling "Task.spawn" explicitly when
|
|
* you want to recurse into other task functions.
|
|
*
|
|
* - The "Task.spawn" function also accepts a primitive value, or a function
|
|
* returning a primitive value, and treats the value as the result of the
|
|
* task. This makes it possible to call an externally provided function and
|
|
* spawn a task from it, regardless of whether it is an asynchronous generator
|
|
* or a synchronous function. This comes in handy when iterating over
|
|
* function lists where some items have been converted to tasks and some not.
|
|
*/
|
|
|
|
// Globals
|
|
|
|
const Cc = Components.classes;
|
|
const Ci = Components.interfaces;
|
|
const Cu = Components.utils;
|
|
const Cr = Components.results;
|
|
|
|
// For now, we're worried about add-ons using Tasks with CPOWs, so we'll
|
|
// permit them in this scope, but this support will go away soon.
|
|
Cu.permitCPOWsInScope(this);
|
|
|
|
Cu.import("resource://gre/modules/Promise.jsm");
|
|
|
|
// The following error types are considered programmer errors, which should be
|
|
// reported (possibly redundantly) so as to let programmers fix their code.
|
|
const ERRORS_TO_REPORT = ["EvalError", "RangeError", "ReferenceError", "TypeError"];
|
|
|
|
/**
|
|
* The Task currently being executed
|
|
*/
|
|
var gCurrentTask = null;
|
|
|
|
/**
|
|
* If `true`, capture stacks whenever entering a Task and rewrite the
|
|
* stack any exception thrown through a Task.
|
|
*/
|
|
var gMaintainStack = false;
|
|
|
|
|
|
/**
|
|
* Iterate through the lines of a string.
|
|
*
|
|
* @return Iterator<string>
|
|
*/
|
|
function* linesOf(string) {
|
|
let reLine = /([^\r\n])+/g;
|
|
let match;
|
|
while ((match = reLine.exec(string))) {
|
|
yield [match[0], match.index];
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Detect whether a value is a generator.
|
|
*
|
|
* @param aValue
|
|
* The value to identify.
|
|
* @return A boolean indicating whether the value is a generator.
|
|
*/
|
|
function isGenerator(aValue) {
|
|
return Object.prototype.toString.call(aValue) == "[object Generator]";
|
|
}
|
|
|
|
// Task
|
|
|
|
/**
|
|
* This object provides the public module functions.
|
|
*/
|
|
this.Task = {
|
|
/**
|
|
* Creates and starts a new task.
|
|
*
|
|
* @param aTask
|
|
* - If you specify a generator function, it is called with no
|
|
* arguments to retrieve the associated iterator. The generator
|
|
* function is a task, that is can yield promise objects to wait
|
|
* upon.
|
|
* - If you specify the iterator returned by a generator function you
|
|
* called, the generator function is also executed as a task. This
|
|
* allows you to call the function with arguments.
|
|
* - If you specify a function that is not a generator, it is called
|
|
* with no arguments, and its return value is used to resolve the
|
|
* returned promise.
|
|
* - If you specify anything else, you get a promise that is already
|
|
* resolved with the specified value.
|
|
*
|
|
* @return A promise object where you can register completion callbacks to be
|
|
* called when the task terminates.
|
|
*/
|
|
spawn: function Task_spawn(aTask) {
|
|
return createAsyncFunction(aTask).call(undefined);
|
|
},
|
|
|
|
/**
|
|
* Create and return an 'async function' that starts a new task.
|
|
*
|
|
* This is similar to 'spawn' except that it doesn't immediately start
|
|
* the task, it binds the task to the async function's 'this' object and
|
|
* arguments, and it requires the task to be a function.
|
|
*
|
|
* It simplifies the common pattern of implementing a method via a task,
|
|
* like this simple object with a 'greet' method that has a 'name' parameter
|
|
* and spawns a task to send a greeting and return its reply:
|
|
*
|
|
* let greeter = {
|
|
* message: "Hello, NAME!",
|
|
* greet: function(name) {
|
|
* return Task.spawn((function* () {
|
|
* return yield sendGreeting(this.message.replace(/NAME/, name));
|
|
* }).bind(this);
|
|
* })
|
|
* };
|
|
*
|
|
* With Task.async, the method can be declared succinctly:
|
|
*
|
|
* let greeter = {
|
|
* message: "Hello, NAME!",
|
|
* greet: Task.async(function* (name) {
|
|
* return yield sendGreeting(this.message.replace(/NAME/, name));
|
|
* })
|
|
* };
|
|
*
|
|
* While maintaining identical semantics:
|
|
*
|
|
* greeter.greet("Mitchell").then((reply) => { ... }); // behaves the same
|
|
*
|
|
* @param aTask
|
|
* The task function to start.
|
|
*
|
|
* @return A function that starts the task function and returns its promise.
|
|
*/
|
|
async: function Task_async(aTask) {
|
|
if (typeof(aTask) != "function") {
|
|
throw new TypeError("aTask argument must be a function");
|
|
}
|
|
|
|
return createAsyncFunction(aTask);
|
|
},
|
|
|
|
/**
|
|
* Constructs a special exception that, when thrown inside a legacy generator
|
|
* function (non-star generator), allows the associated task to be resolved
|
|
* with a specific value.
|
|
*
|
|
* Example: throw new Task.Result("Value");
|
|
*/
|
|
Result: function Task_Result(aValue) {
|
|
this.value = aValue;
|
|
}
|
|
};
|
|
|
|
function createAsyncFunction(aTask) {
|
|
let asyncFunction = function() {
|
|
let result = aTask;
|
|
if (aTask && typeof(aTask) == "function") {
|
|
if (aTask.isAsyncFunction) {
|
|
throw new TypeError(
|
|
"Cannot use an async function in place of a promise. " +
|
|
"You should either invoke the async function first " +
|
|
"or use 'Task.spawn' instead of 'Task.async' to start " +
|
|
"the Task and return its promise.");
|
|
}
|
|
|
|
try {
|
|
// Let's call into the function ourselves.
|
|
result = aTask.apply(this, arguments);
|
|
} catch (ex) {
|
|
if (ex instanceof Task.Result) {
|
|
return Promise.resolve(ex.value);
|
|
}
|
|
return Promise.reject(ex);
|
|
}
|
|
}
|
|
|
|
if (isGenerator(result)) {
|
|
// This is an iterator resulting from calling a generator function.
|
|
return new TaskImpl(result).deferred.promise;
|
|
}
|
|
|
|
// Just propagate the given value to the caller as a resolved promise.
|
|
return Promise.resolve(result);
|
|
};
|
|
|
|
asyncFunction.isAsyncFunction = true;
|
|
|
|
return asyncFunction;
|
|
}
|
|
|
|
// TaskImpl
|
|
|
|
/**
|
|
* Executes the specified iterator as a task, and gives access to the promise
|
|
* that is fulfilled when the task terminates.
|
|
*/
|
|
function TaskImpl(iterator) {
|
|
if (gMaintainStack) {
|
|
this._stack = (new Error()).stack;
|
|
}
|
|
this.deferred = Promise.defer();
|
|
this._iterator = iterator;
|
|
this._isStarGenerator = !("send" in iterator);
|
|
this._run(true);
|
|
}
|
|
|
|
TaskImpl.prototype = {
|
|
/**
|
|
* Includes the promise object where task completion callbacks are registered,
|
|
* and methods to resolve or reject the promise at task completion.
|
|
*/
|
|
deferred: null,
|
|
|
|
/**
|
|
* The iterator returned by the generator function associated with this task.
|
|
*/
|
|
_iterator: null,
|
|
|
|
/**
|
|
* Whether this Task is using a star generator.
|
|
*/
|
|
_isStarGenerator: false,
|
|
|
|
/**
|
|
* Main execution routine, that calls into the generator function.
|
|
*
|
|
* @param aSendResolved
|
|
* If true, indicates that we should continue into the generator
|
|
* function regularly (if we were waiting on a promise, it was
|
|
* resolved). If true, indicates that we should cause an exception to
|
|
* be thrown into the generator function (if we were waiting on a
|
|
* promise, it was rejected).
|
|
* @param aSendValue
|
|
* Resolution result or rejection exception, if any.
|
|
*/
|
|
_run: function TaskImpl_run(aSendResolved, aSendValue) {
|
|
|
|
try {
|
|
gCurrentTask = this;
|
|
|
|
if (this._isStarGenerator) {
|
|
if (Cu.isDeadWrapper(this._iterator)) {
|
|
this.deferred.resolve(undefined);
|
|
} else {
|
|
try {
|
|
let result = aSendResolved ? this._iterator.next(aSendValue)
|
|
: this._iterator.throw(aSendValue);
|
|
|
|
if (result.done) {
|
|
// The generator function returned.
|
|
this.deferred.resolve(result.value);
|
|
} else {
|
|
// The generator function yielded.
|
|
this._handleResultValue(result.value);
|
|
}
|
|
} catch (ex) {
|
|
// The generator function failed with an uncaught exception.
|
|
this._handleException(ex);
|
|
}
|
|
}
|
|
} else {
|
|
try {
|
|
let yielded = aSendResolved ? this._iterator.send(aSendValue)
|
|
: this._iterator.throw(aSendValue);
|
|
this._handleResultValue(yielded);
|
|
} catch (ex) {
|
|
if (ex instanceof Task.Result) {
|
|
// The generator function threw the special exception that allows it to
|
|
// return a specific value on resolution.
|
|
this.deferred.resolve(ex.value);
|
|
} else if (ex instanceof StopIteration) {
|
|
// The generator function terminated with no specific result.
|
|
this.deferred.resolve(undefined);
|
|
} else {
|
|
// The generator function failed with an uncaught exception.
|
|
this._handleException(ex);
|
|
}
|
|
}
|
|
}
|
|
} finally {
|
|
//
|
|
// At this stage, the Task may have finished executing, or have
|
|
// walked through a `yield` or passed control to a sub-Task.
|
|
// Regardless, if we still own `gCurrentTask`, reset it. If we
|
|
// have not finished execution of this Task, re-entering `_run`
|
|
// will set `gCurrentTask` to `this` as needed.
|
|
//
|
|
// We just need to be careful here in case we hit the following
|
|
// pattern:
|
|
//
|
|
// Task.spawn(foo);
|
|
// Task.spawn(bar);
|
|
//
|
|
// Here, `foo` and `bar` may be interleaved, so when we finish
|
|
// executing `foo`, `gCurrentTask` may actually either `foo` or
|
|
// `bar`. If `gCurrentTask` has already been set to `bar`, leave
|
|
// it be and it will be reset to `null` once `bar` is complete.
|
|
//
|
|
if (gCurrentTask == this) {
|
|
gCurrentTask = null;
|
|
}
|
|
}
|
|
},
|
|
|
|
/**
|
|
* Handle a value yielded by a generator.
|
|
*
|
|
* @param aValue
|
|
* The yielded value to handle.
|
|
*/
|
|
_handleResultValue: function TaskImpl_handleResultValue(aValue) {
|
|
// If our task yielded an iterator resulting from calling another
|
|
// generator function, automatically spawn a task from it, effectively
|
|
// turning it into a promise that is fulfilled on task completion.
|
|
if (isGenerator(aValue)) {
|
|
aValue = Task.spawn(aValue);
|
|
}
|
|
|
|
if (aValue && typeof(aValue.then) == "function") {
|
|
// We have a promise object now. When fulfilled, call again into this
|
|
// function to continue the task, with either a resolution or rejection
|
|
// condition.
|
|
aValue.then(this._run.bind(this, true),
|
|
this._run.bind(this, false));
|
|
} else {
|
|
// If our task yielded a value that is not a promise, just continue and
|
|
// pass it directly as the result of the yield statement.
|
|
this._run(true, aValue);
|
|
}
|
|
},
|
|
|
|
/**
|
|
* Handle an uncaught exception thrown from a generator.
|
|
*
|
|
* @param aException
|
|
* The uncaught exception to handle.
|
|
*/
|
|
_handleException: function TaskImpl_handleException(aException) {
|
|
|
|
gCurrentTask = this;
|
|
|
|
if (aException && typeof aException == "object" && "stack" in aException) {
|
|
|
|
let stack = aException.stack;
|
|
|
|
if (gMaintainStack &&
|
|
aException._capturedTaskStack != this._stack &&
|
|
typeof stack == "string") {
|
|
|
|
// Rewrite the stack for more readability.
|
|
|
|
let bottomStack = this._stack;
|
|
let topStack = stack;
|
|
|
|
stack = Task.Debugging.generateReadableStack(stack);
|
|
|
|
aException.stack = stack;
|
|
|
|
// If aException is reinjected in the same task and rethrown,
|
|
// we don't want to perform the rewrite again.
|
|
aException._capturedTaskStack = bottomStack;
|
|
} else if (!stack) {
|
|
stack = "Not available";
|
|
}
|
|
|
|
if ("name" in aException &&
|
|
ERRORS_TO_REPORT.indexOf(aException.name) != -1) {
|
|
|
|
// We suspect that the exception is a programmer error, so we now
|
|
// display it using dump(). Note that we do not use Cu.reportError as
|
|
// we assume that this is a programming error, so we do not want end
|
|
// users to see it. Also, if the programmer handles errors correctly,
|
|
// they will either treat the error or log them somewhere.
|
|
|
|
dump("*************************\n");
|
|
dump("A coding exception was thrown and uncaught in a Task.\n\n");
|
|
dump("Full message: " + aException + "\n");
|
|
dump("Full stack: " + aException.stack + "\n");
|
|
dump("*************************\n");
|
|
}
|
|
}
|
|
|
|
this.deferred.reject(aException);
|
|
},
|
|
|
|
get callerStack() {
|
|
// Cut `this._stack` at the last line of the first block that
|
|
// contains Task.jsm, keep the tail.
|
|
for (let [line, index] of linesOf(this._stack || "")) {
|
|
if (line.indexOf("/Task.jsm:") == -1) {
|
|
return this._stack.substring(index);
|
|
}
|
|
}
|
|
return "";
|
|
}
|
|
};
|
|
|
|
|
|
Task.Debugging = {
|
|
|
|
/**
|
|
* Control stack rewriting.
|
|
*
|
|
* If `true`, any exception thrown from a Task will be rewritten to
|
|
* provide a human-readable stack trace. Otherwise, stack traces will
|
|
* be left unchanged.
|
|
*
|
|
* There is a (small but existing) runtime cost associated to stack
|
|
* rewriting, so you should probably not activate this in production
|
|
* code.
|
|
*
|
|
* @type {bool}
|
|
*/
|
|
get maintainStack() {
|
|
return gMaintainStack;
|
|
},
|
|
set maintainStack(x) {
|
|
if (!x) {
|
|
gCurrentTask = null;
|
|
}
|
|
return gMaintainStack = x;
|
|
},
|
|
|
|
/**
|
|
* Generate a human-readable stack for an error raised in
|
|
* a Task.
|
|
*
|
|
* @param {string} topStack The stack provided by the error.
|
|
* @param {string=} prefix Optionally, a prefix for each line.
|
|
*/
|
|
generateReadableStack: function(topStack, prefix = "") {
|
|
if (!gCurrentTask) {
|
|
return topStack;
|
|
}
|
|
|
|
// Cut `topStack` at the first line that contains Task.jsm, keep the head.
|
|
let lines = [];
|
|
for (let [line] of linesOf(topStack)) {
|
|
if (line.indexOf("/Task.jsm:") != -1) {
|
|
break;
|
|
}
|
|
lines.push(prefix + line);
|
|
}
|
|
if (!prefix) {
|
|
lines.push(gCurrentTask.callerStack);
|
|
} else {
|
|
for (let [line] of linesOf(gCurrentTask.callerStack)) {
|
|
lines.push(prefix + line);
|
|
}
|
|
}
|
|
|
|
return lines.join("\n");
|
|
}
|
|
};
|