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Auto merge of #8768 - vegayours:8616_intermittent_option_unwrap_in_timers, r=jdm

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fix intermittent Option::unwrap in timers

fixes intermittent #8616

This intermittent indicates real problem in code.
Lets consider such code:
```javascript
// timer 1
setTimeout(function() {
     //timer 2
     setTimeout(function() {}, 0);
}, 0);
```
When we receive event to fire timer 1 it will be selected and extracted from active timers list in fire_timer function. During timer 1 handler execution we will schedule timer 2 and request timer event for it. But it will be executed during same fire_timer call because of 0 timeout. And as a result we will have empty timers list and expecting event for timer 2 that will crash in assert.

I'm not sure that all I've written is clear, but we have something like this:
```
install timer 1 -> [1] in timers list
push and expect timer event 1 -> expected_event=1
received timer event 1
    fire_timer()
         select timer 1 to execute -> [] in timers list
         execute timer 1 handler
             install timer 2 -> [2] in timers list
             push and expect timer event 2 -> expected_event=2
         select timer 2 to execute (because of 0 timeout) -> [] in tiemrs list
         execute timer 2 handler
expected_event=2 is dangling
received timer event 2
    fire_timer() -> BOOM
```

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This commit is contained in:
bors-servo 2015-12-04 21:19:58 +05:30
commit b32128e299
4 changed files with 55 additions and 8 deletions
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14
components/script/timers.rs
View file

@ -23,7 +23,7 @@ use std::rc::Rc;
use util::mem::HeapSizeOf;
use util::str::DOMString;
#[derive(JSTraceable, PartialEq, Eq, Copy, Clone, HeapSizeOf, Hash, PartialOrd, Ord)]
#[derive(JSTraceable, PartialEq, Eq, Copy, Clone, HeapSizeOf, Hash, PartialOrd, Ord, Debug)]
pub struct TimerHandle(i32);
#[derive(JSTraceable, HeapSizeOf)]
@ -253,16 +253,22 @@ impl ActiveTimers {
// Since the event id was the expected one, at least one timer should be due.
assert!(base_time >= self.timers.borrow().last().unwrap().next_call);
// select timers to run to prevent firing timers
// that were installed during fire of another timer
let mut timers_to_run: Vec<Timer> = Vec::new();
loop {
let timer = {
let mut timers = self.timers.borrow_mut();
if timers.is_empty() || timers.last().unwrap().next_call > base_time {
break;
}
timers.pop().unwrap()
};
timers_to_run.push(timers.pop().unwrap());
}
for timer in timers_to_run {
let callback = timer.callback.clone();
// prep for step 6 in nested set_timeout_or_interval calls

6
tests/wpt/mozilla/meta/MANIFEST.json
View file

@ -5757,6 +5757,12 @@
"url": "/_mozilla/mozilla/textcontent.html"
}
],
"mozilla/timer_eventInvalidation.html": [
{
"path": "mozilla/timer_eventInvalidation.html",
"url": "/_mozilla/mozilla/timer_eventInvalidation.html"
}
],
"mozilla/title.html": [
{
"path": "mozilla/title.html",

21
tests/wpt/mozilla/tests/mozilla/timer_eventInvalidation.html Normal file
View file

@ -0,0 +1,21 @@
<html>
<head>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
</head>
<body>
<script>
async_test(function(test) {
// couldn't reproduce this behaviour without iframe
var iframe = document.createElement('iframe');
window.addEventListener('test_done', function() {
// if event invalidation is not properly implemented
// servo will crash during a short period of time
setTimeout(() => test.done(), 50);
}, false);
iframe.src = 'timer_eventInvalidation_test.html';
document.body.appendChild(iframe);
});
</script>
</body>
</html>

14
tests/wpt/mozilla/tests/mozilla/timer_eventInvalidation_test.html Normal file
View file

@ -0,0 +1,14 @@
<html>
<head>
</head>
<body>
<script>
setTimeout(function() {
setTimeout(function() {
var e = new Event('test_done');
window.parent.dispatchEvent(e);
}, 0);
}, 0);
</script>
</body>
</html>