mozilla-central/dom/base/test/test_timeout_clamp.html

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Test Info:

<!DOCTYPE HTML>
<html>
<!--
-->
<head>
<meta charset="utf-8">
<title>Test for Bug 1378586</title>
<script src="/tests/SimpleTest/SimpleTest.js"></script>
<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
</head>
<body>
<script>
SimpleTest.waitForExplicitFinish();
// We need to clear our nesting level periodically. We do this by firing
// a postMessage() to get a runnable on the event loop without any setTimeout()
// nesting.
function clearNestingLevel() {
return new Promise(resolve => {
window.addEventListener('message', () => {
resolve();
}, {once: true});
postMessage('done', '*');
});
}
function delayByTimeoutChain(iterations) {
return new Promise(resolve => {
let count = 0;
function tick() {
count += 1;
if (count >= iterations) {
resolve();
return;
}
setTimeout(tick, 0);
}
setTimeout(tick, 0);
});
}
function delayByInterval(iterations) {
return new Promise(resolve => {
let count = 0;
function tick() {
count += 1;
if (count >= iterations) {
resolve();
}
}
setInterval(tick, 0);
});
}
function testNestedIntervals() {
return new Promise(resolve => {
const runCount = 100;
let counter = 0;
let intervalId = 0;
let prevInitTime = performance.now();
let totalTime = 0;
function intervalCallback() {
let now = performance.now();
let delay = now - prevInitTime;
totalTime += delay;
prevInitTime = now;
clearInterval(intervalId);
if (++counter < runCount) {
intervalId = setInterval(intervalCallback, 0);
} else {
// Delays should be clamped to 4ms after the initial calls, but allow
// some fuzziness, so divide by 2.
let expectedTime = runCount * 4 / 2;
ok(totalTime > expectedTime, "Should not run callbacks too fast.");
resolve();
}
}
// Use the timeout value defined in the spec, 4ms.
SpecialPowers.pushPrefEnv({ 'set': [["dom.min_timeout_value", 4]]},
intervalCallback);
});
}
// Use a very long clamp delay to make it easier to measure the change
// in automation. Some of our test servers are very slow and noisy.
const clampDelayMS = 10000;
// We expect that we will clamp on the 5th callback. This should
// be the same for both setTimeout() chains and setInterval().
const expectedClampIteration = 5;
async function runTests() {
// Things like pushPrefEnv() can use setTimeout() internally which may give
// us a nesting level. Clear the nesting level to start so this doesn't
// confuse the test.
await clearNestingLevel();
// Verify a setTimeout() chain clamps correctly
let start = performance.now();
await delayByTimeoutChain(expectedClampIteration);
let stop = performance.now();
let delta = stop - start;
ok(delta >= clampDelayMS, "setTimeout() chain clamped: " + stop + " - " + start + " = " + delta);
ok(delta < (2*clampDelayMS), "setTimeout() chain did not clamp twice");
await clearNestingLevel();
// Verify setInterval() clamps correctly
start = performance.now();
await delayByInterval(expectedClampIteration);
stop = performance.now();
delta = stop - start;
ok(delta >= clampDelayMS, "setInterval() clamped: " + stop + " - " + start + " = " + delta);
ok(delta < (2*clampDelayMS), "setInterval() did not clamp twice");
await clearNestingLevel();
// Verify a setTimeout() chain will continue to clamp past the first
// expected iteration.
const expectedDelay = (1 + expectedClampIteration) * clampDelayMS;
start = performance.now();
await delayByTimeoutChain(2 * expectedClampIteration);
stop = performance.now();
delta = stop - start;
ok(delta >= expectedDelay, "setTimeout() chain continued to clamp: " + stop + " - " + start + " = " + delta);
await clearNestingLevel();
// Verify setInterval() will continue to clamp past the first expected
// iteration.
start = performance.now();
await delayByTimeoutChain(2 * expectedClampIteration);
stop = performance.now();
delta = stop - start;
ok(delta >= expectedDelay, "setInterval() continued to clamp: " + stop + " - " + start + " = " + delta);
await testNestedIntervals();
SimpleTest.finish();
}
// It appears that it's possible to get unlucky with time jittering and fail this test.
// If start is jittered upwards, everything executes very quickly, and delta has
// a very high midpoint, we may have taken between 10 and 10.002 seconds to execute; but
// it will appear to be 9.998. Turn off jitter (and add logging) to test this.
SpecialPowers.pushPrefEnv({ 'set': [
["dom.min_timeout_value", clampDelayMS],
["privacy.resistFingerprinting.reduceTimerPrecision.jitter", false],
]}, runTests);
</script>
</body>
</html>