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204 lines
6.3 KiB
JavaScript
204 lines
6.3 KiB
JavaScript
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef MERGED_COMPARTMENT
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this.EXPORTED_SYMBOLS = ["Async"];
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const {classes: Cc, interfaces: Ci, results: Cr, utils: Cu} = Components;
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#endif
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// Constants for makeSyncCallback, waitForSyncCallback.
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const CB_READY = {};
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const CB_COMPLETE = {};
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const CB_FAIL = {};
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const REASON_ERROR = Ci.mozIStorageStatementCallback.REASON_ERROR;
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Cu.import("resource://gre/modules/Services.jsm");
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/*
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* Helpers for various async operations.
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*/
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this.Async = {
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/**
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* Execute an arbitrary number of asynchronous functions one after the
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* other, passing the callback arguments on to the next one. All functions
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* must take a callback function as their last argument. The 'this' object
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* will be whatever chain()'s is.
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*
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* @usage this._chain = Async.chain;
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* this._chain(this.foo, this.bar, this.baz)(args, for, foo)
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*
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* This is equivalent to:
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*
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* let self = this;
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* self.foo(args, for, foo, function (bars, args) {
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* self.bar(bars, args, function (baz, params) {
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* self.baz(baz, params);
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* });
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* });
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*/
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chain: function chain() {
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let funcs = Array.slice(arguments);
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let thisObj = this;
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return function callback() {
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if (funcs.length) {
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let args = Array.slice(arguments).concat(callback);
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let f = funcs.shift();
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f.apply(thisObj, args);
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}
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};
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},
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/**
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* Helpers for making asynchronous calls within a synchronous API possible.
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*
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* If you value your sanity, do not look closely at the following functions.
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*/
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/**
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* Create a sync callback that remembers state, in particular whether it has
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* been called.
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* The returned callback can be called directly passing an optional arg which
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* will be returned by waitForSyncCallback(). The callback also has a
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* .throw() method, which takes an error object and will cause
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* waitForSyncCallback to fail with the error object thrown as an exception
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* (but note that the .throw method *does not* itself throw - it just causes
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* the wait function to throw).
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*/
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makeSyncCallback: function makeSyncCallback() {
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// The main callback remembers the value it was passed, and that it got data.
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let onComplete = function onComplete(data) {
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onComplete.state = CB_COMPLETE;
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onComplete.value = data;
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};
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// Initialize private callback data in preparation for being called.
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onComplete.state = CB_READY;
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onComplete.value = null;
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// Allow an alternate callback to trigger an exception to be thrown.
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onComplete.throw = function onComplete_throw(data) {
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onComplete.state = CB_FAIL;
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onComplete.value = data;
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};
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return onComplete;
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},
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/**
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* Wait for a sync callback to finish.
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*/
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waitForSyncCallback: function waitForSyncCallback(callback) {
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// Grab the current thread so we can make it give up priority.
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let thread = Cc["@mozilla.org/thread-manager;1"].getService().currentThread;
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// Keep waiting until our callback is triggered (unless the app is quitting).
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while (Async.checkAppReady() && callback.state == CB_READY) {
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thread.processNextEvent(true);
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}
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// Reset the state of the callback to prepare for another call.
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let state = callback.state;
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callback.state = CB_READY;
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// Throw the value the callback decided to fail with.
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if (state == CB_FAIL) {
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throw callback.value;
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}
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// Return the value passed to the callback.
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return callback.value;
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},
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/**
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* Check if the app is still ready (not quitting).
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*/
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checkAppReady: function checkAppReady() {
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// Watch for app-quit notification to stop any sync calls
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Services.obs.addObserver(function onQuitApplication() {
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Services.obs.removeObserver(onQuitApplication, "quit-application");
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Async.checkAppReady = function() {
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throw Components.Exception("App. Quitting", Cr.NS_ERROR_ABORT);
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};
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}, "quit-application", false);
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// In the common case, checkAppReady just returns true
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return (Async.checkAppReady = function() { return true; })();
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},
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/**
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* Return the two things you need to make an asynchronous call synchronous
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* by spinning the event loop.
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*/
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makeSpinningCallback: function makeSpinningCallback() {
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let cb = Async.makeSyncCallback();
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function callback(error, ret) {
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if (error)
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cb.throw(error);
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else
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cb(ret);
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}
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callback.wait = function() Async.waitForSyncCallback(cb);
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return callback;
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},
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// Prototype for mozIStorageCallback, used in querySpinningly.
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// This allows us to define the handle* functions just once rather
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// than on every querySpinningly invocation.
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_storageCallbackPrototype: {
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results: null,
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// These are set by queryAsync.
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names: null,
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syncCb: null,
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handleResult: function handleResult(results) {
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if (!this.names) {
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return;
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}
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if (!this.results) {
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this.results = [];
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}
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let row;
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while ((row = results.getNextRow()) != null) {
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let item = {};
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for each (let name in this.names) {
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item[name] = row.getResultByName(name);
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}
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this.results.push(item);
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}
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},
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handleError: function handleError(error) {
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this.syncCb.throw(error);
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},
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handleCompletion: function handleCompletion(reason) {
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// If we got an error, handleError will also have been called, so don't
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// call the callback! We never cancel statements, so we don't need to
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// address that quandary.
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if (reason == REASON_ERROR)
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return;
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// If we were called with column names but didn't find any results,
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// the calling code probably still expects an array as a return value.
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if (this.names && !this.results) {
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this.results = [];
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}
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this.syncCb(this.results);
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}
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},
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querySpinningly: function querySpinningly(query, names) {
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// 'Synchronously' asyncExecute, fetching all results by name.
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let storageCallback = {names: names,
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syncCb: Async.makeSyncCallback()};
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storageCallback.__proto__ = Async._storageCallbackPrototype;
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query.executeAsync(storageCallback);
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return Async.waitForSyncCallback(storageCallback.syncCb);
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},
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};
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