Revision 742259 of ChromeWorker

<p>{{ gecko_minversion_header("2") }}</p>

<p>{{ non-standard_header() }}</p>

<p>{{ APIRef("Web Workers") }}</p>

<h2 id="Summary">Summary</h2>

<p>If you're developing privileged code, and would like to create a worker that can use <a href="/en/js-ctypes" title="en/js-ctypes">js-ctypes</a> to perform calls to native code, you can do so by using <code>ChromeWorker</code> instead of the standard {{ domxref("Worker") }} object. It works exactly like a standard {{ domxref("Worker") }}, except that it has access to <a href="/en/js-ctypes" title="en/js-ctypes">js-ctypes</a> via a global <code>ctypes</code> object available in the global scope of the worker.</p>

<p>Addons must use absolute URLs to load their workers, and that those URLs have to be using a <code>chrome://</code> or <code>resource://</code> protocol (<code>file://</code> is not accepted.) Addons that wish to use <code>file://</code> URLs must first register a resource replacement path, using code like this:</p>

<pre class="brush: js">
var fileuri = Services.io.newFileURI(file);
Services.io.getProtocolHandler("resource").
              QueryInterface(Ci.nsIResProtocolHandler).
              setSubstitution("my-cool-addon", fileuri);
  var worker = new Worker("resource://my-cool-addon/worker.js");</pre>

<p>More references:</p>

<ul>
 <li>You can use <code>ChromeWorker</code> from <a href="/en/JavaScript_code_modules" title="en/JavaScript code modules">JavaScript code modules</a>. See <a href="/en/JavaScript_code_modules/Using_workers_in_JavaScript_code_modules" title="en/JavaScript code modules/Using workers in JavaScript code modules">Using workers in JavaScript code modules</a> for details.</li>
 <li>You can use <a href="https://developer.mozilla.org/en-US/docs/Mozilla/ChromeWorkers/Chrome_Worker_Modules">ChromeWorker modules</a> in ChromeWorkers.</li>
 <li>See <a class="internal" href="/En/Using_web_workers" title="en/Using DOM workers">Using web workers</a> for examples and details.</li>
</ul>

<h2 id="Using_XPCOM_from_chrome_workers">Using XPCOM from chrome workers</h2>

<p>{{ obsolete_header("8.0") }}</p>

<div class="note">
<p><strong>Note:</strong> Support for using XPCOM and XPConnect from <code>ChromeWorker</code>s was removed in {{Gecko("8.0")}} when workers were updated to run in their own operating system level threads, with one thread per worker. See {{ bug(649537) }} for details.</p>
</div>

<p>Prior to Gecko 8.0 {{ geckoRelease("8.0") }}, you could use the {{ domxref("Worker") }} <code>postMessage()</code> method to send <a href="/en/XPConnect_wrappers#XPCWrappedNative" title="en/XPConnect wrappers#XPCWrappedNative"><code>XPCWrappedNative</code></a> objects to chrome workers, as long as the underlying object is marked with the <code>nsIClassInfo.THREADSAFE</code> flag, which indicates that the object is safe to access from multiple threads at once.</p>

<p>In addition, <code>ChromeWorker</code> objects have access to a new global XPCOM&nbsp;object -- which is only available to chrome workers -- which has two methods:</p>

<dl>
 <dt><code>createInstance()</code></dt>
 <dd>Creates an instance of an XPCOM&nbsp;interface. Accepts a single parameter: the contract ID of the interface to create an instance of.</dd>
 <dt><code>getService()</code></dt>
 <dd>Returns the shared global service object for the specified XPCOM&nbsp;interface. Accepts a single parameter: the contract ID of the interface to which you wish to obtain a reference.</dd>
</dl>

<h3 id="Using_the_XPCOM_object">Using the XPCOM&nbsp;object</h3>

<p>Before using the XPCOM&nbsp;object to create instances or access services, it's important to note that this only works with components that are thread safe; if you try to do so with a component that isn't thread safe, an exception will be thrown.</p>

<h4 id="Creating_instances_of_components">Creating instances of components</h4>

<p>If your worker wants to create a thread pool in which it can create additional threads, you can do this:</p>

<pre>
let myThreadPool = XPCOM.createInstance("@mozilla.org/thread-pool;1");
myThreadPool.threadLimit = 6;
/* send some events with the pool */
myThreadPool.shutdown();</pre>

<h4 id="Passing_objects_to_chrome_workers">Passing objects to chrome workers</h4>

<p>Thread safe objects can be passed to chrome workers using the <code>postMessage()</code>&nbsp;method. Attempting to pass a non-thread safe object will throw an exception.</p>

<pre>
/* create a new thread, then pass it to the worker */

var thread = Components.classes["@mozilla.org/thread-manager;1"].getService().newThread(0);
worker.postMessage(thread); </pre>

<h2 id="See_also">See also</h2>

<ul>
 <li><a class="internal" href="/En/Using_web_workers" title="en/Using DOM workers">Using web workers</a></li>
 <li><a href="/en/JavaScript_code_modules/Using_workers_in_JavaScript_code_modules" title="en/JavaScript code modules/Using workers in JavaScript code modules">Using workers in JavaScript code modules</a></li>
 <li>{{ domxref("Worker") }}</li>
 <li><code><a class="internal" href="/En/DOM/SharedWorker" title="en/DOM/SharedWorker">SharedWorker</a></code></li>
 <li><a class="external" href="https://www.whatwg.org/specs/web-workers/current-work/" title="https://www.whatwg.org/specs/web-workers/current-work/">Web Workers specification</a></li>
 <li>{{ domxref("WorkerGlobalScope") }}</li>
 <li><a href="https://github.com/Noitidart/ChromeWorker">GitHub :: ChromeWorker</a> - A fully working demo addon using js-ctypes from a chrome worker. Uses WinAPI example.</li>
 <li><a href="https://github.com/Noitidart/PromiseWorker">GitHub :: PromiseWorker</a> - Shows how to ues promises as an twist on postMessage feature of ChromeWorker</li>
</ul>