gecko/services/common/async.js

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