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"use strict";
// The debugger uses nsIDOMWindowUtils::suspendTimeouts and ...::resumeTimeouts
// to ensure that content event handlers do not run while a JavaScript
// invocation is stepping or paused at a breakpoint. If a worker thread sends
// messages to the content while the content is paused, those messages must not
// run until the JavaScript invocation interrupted by the debugger has completed.
//
// Bug 1426467 is that calling nsIDOMWindowUtils::resumeTimeouts actually
// delivers deferred messages itself, calling the content's 'onmessage' handler.
// But the debugger calls suspend/resume around each individual interruption of
// the debuggee -- each step, say -- meaning that hitting the "step into" button
// causes you to step from the debuggee directly into an onmessage handler,
// since the onmessage handler is the next function call the debugger sees.
//
// In other words, delivering deferred messages from resumeTimeouts, as it is
// used by the debugger, breaks the run-to-completion rule. They must not be
// delivered until after the JavaScript invocation at hand is complete. That's
// what this test checks.
//
// For this test to detect the bug, the following steps must take place in
// order:
//
// 1) The content page must call suspendTimeouts.
// 2) A runnable conveying a message from the worker thread must attempt to
// deliver the message, see that the content page has suspended such things,
// and hold the message for later delivery.
// 3) The content page must call resumeTimeouts.
//
// In a correct implementation, the message from the worker thread is delivered
// only after the main thread returns to the event loop after calling
// resumeTimeouts in step 3). In the buggy implementation, the onmessage handler
// is called directly from the call to resumeTimeouts, so that the onmessage
// handlers run in the midst of whatever JavaScript invocation resumed timeouts
// (say, stepping in the debugger), in violation of the run-to-completion rule.
//
// In this specific bug, the handlers are called from resumeTimeouts, but
// really, running them any time before that invocation returns to the main
// event loop would be a bug.
//
// Posting the message and calling resumeTimeouts take place in different
// threads, but if 2) and 3) don't occur in that order, the worker's message
// will never be delayed and the test will pass spuriously. But the worker
// can't communicate with the content page directly, to let it know that it
// should proceed with step 3): the purpose of suspendTimeouts is to pause
// all such communication.
//
// So instead, the content page creates a MessageChannel, and passes one
// MessagePort to the worker and the other to this mochitest (which has its
// own window, separate from the one calling suspendTimeouts). The worker
// notifies the mochitest when it has posted the message, and then the
// mochitest calls into the content to carry out step 3).
// To help you follow all the callbacks and event handlers, this code pulls out
// event handler functions so that control flows from top to bottom.
window.onload = function() {
// This mochitest is not complete until we call SimpleTest.finish. Don't just
// exit as soon as we return to the main event loop.
SimpleTest.waitForExplicitFinish();
const iframe = document.createElement("iframe");
iframe.src =
"http://mochi.test:8888/chrome/devtools/server/tests/chrome/suspendTimeouts_content.html";
iframe.onload = iframe_onload_handler;
document.body.appendChild(iframe);
function iframe_onload_handler() {
const content = iframe.contentWindow.wrappedJSObject;
const windowUtils = iframe.contentWindow.windowUtils;
// Hand over the suspend and resume functions to the content page, along
// with some testing utilities.
content.suspendTimeouts = function() {
SimpleTest.info("test_suspendTimeouts", "calling suspendTimeouts");
windowUtils.suspendTimeouts();
};
content.resumeTimeouts = function() {
windowUtils.resumeTimeouts();
SimpleTest.info("test_suspendTimeouts", "resumeTimeouts called");
};
content.info = function(message) {
SimpleTest.info("suspendTimeouts_content.js", message);
};
content.ok = SimpleTest.ok;
content.finish = finish;
SimpleTest.info(
"Disappointed with National Tautology Day? Well, it is what it is."
);
// Once the worker has sent a message to its parent (which should get delayed),
// it sends us a message directly on this channel.
const workerPort = content.create_channel();
workerPort.onmessage = handle_worker_echo;
// Have content send the worker a message that it should echo back to both
// content and us. The echo to content should get delayed; the echo to us
// should cause our handle_worker_echo to be called.
content.start_worker();
function handle_worker_echo({ data }) {
info(`mochitest received message from worker: ${data}`);
// As it turns out, it's not correct to assume that, if the worker posts a
// message to its parent via the global `postMessage` function, and then
// posts a message to the mochitest via the MessagePort, those two
// messages will be delivered in the order they were sent.
//
// - Messages sent via the worker's global's postMessage go through two
// ThrottledEventQueues (one in the worker, and one on the parent), and
// eventually find their way into the thread's primary event queue,
// which is a PrioritizedEventQueue.
//
// - Messages sent via a MessageChannel whose ports are owned by different
// threads are passed as IPDL messages.
//
// There's basically no reliable way to ensure that delivery to content
// has been attempted and the runnable deferred; there are too many
// variables affecting the order in which things are processed. Delaying
// for a second is the best I could think of.
//
// Fortunately, this tactic failing can only cause spurious test passes
// (the runnable never gets deferred, so things work by accident), not
// spurious failures. Without some kind of trustworthy notification that
// the runnable has been deferred, perhaps via some special white-box
// testing API, we can't do better.
setTimeout(() => {
content.resume_timeouts();
}, 1000);
}
function finish(message) {
SimpleTest.info("suspendTimeouts_content.js", "called finish");
SimpleTest.finish();
}
}
};
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