Bug 194111 – Web Inspector: Memory timeline starts from zero when both CPU and Memory timeline are enabled

• Status: RESOLVED
• Resolution: FIXED
• Component: Web Inspector

[Joseph Pecoraro]

Memory timeline starts from zero when both CPU and Memory timeline are enabled

Steps to Reproduce:
1. Inspect this page
2. Show CPU and Memory Timelines
3. Reload page
  => Memory starts from zero

Notes:
- The ResourceUsageThread starts immediately when the first listener (CPU) is added therefore misses values for the second listener (Memory) until the second sample 500ms later. We should start with a small wait to give multiple unique listeners a chance to register before the first sample.

[Radar WebKit Bug Importer]

<rdar://problem/47714555>

[Joseph Pecoraro]

Created attachment 360786 [details]
[PATCH] Proposed Fix

[Devin Rousso]

Comment on attachment 360786 [details]
[PATCH] Proposed Fix

View in context: https://bugs.webkit.org/attachment.cgi?id=360786&action=review

rs=me

> Source/WebCore/page/ResourceUsageThread.cpp:85
> +        WTF::sleep(10_ms);

Where did the `10_ms` come from?  Is there any justification as to why that value was chosen?

> Source/WebCore/page/ResourceUsageThread.cpp:127
> +    WTF::sleep(10_ms);

Should we also be waiting in the case that we already have observers?

[Joseph Pecoraro]

(In reply to Devin Rousso from comment #3)
> Comment on attachment 360786 [details]
> [PATCH] Proposed Fix
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=360786&action=review
> 
> rs=me
> 
> > Source/WebCore/page/ResourceUsageThread.cpp:85
> > +        WTF::sleep(10_ms);
> 
> Where did the `10_ms` come from?  Is there any justification as to why that
> value was chosen?

Nope, the sample rate is 500ms, so this is just a small pause. I do not have a good reason for 10, other then it is small. And allows enough time for other listeners to be activated.

> > Source/WebCore/page/ResourceUsageThread.cpp:127
> > +    WTF::sleep(10_ms);
> 
> Should we also be waiting in the case that we already have observers?

That is what `waitUntilObservers` does. If we waited in there we will have this 10ms pause.

[Devin Rousso]

Comment on attachment 360786 [details]
[PATCH] Proposed Fix

View in context: https://bugs.webkit.org/attachment.cgi?id=360786&action=review

>>> Source/WebCore/page/ResourceUsageThread.cpp:127
>>> +    WTF::sleep(10_ms);
>> 
>> Should we also be waiting in the case that we already have observers?
> 
> That is what `waitUntilObservers` does. If we waited in there we will have this 10ms pause.

I meant more of "why are we also waiting here if we're already waiting inside `waitUntilObservers`?"

[Joseph Pecoraro]

https://trac.webkit.org/changeset/240868/webkit

[Joseph Pecoraro]

Comment on attachment 360786 [details]
[PATCH] Proposed Fix

View in context: https://bugs.webkit.org/attachment.cgi?id=360786&action=review

>>>> Source/WebCore/page/ResourceUsageThread.cpp:127
>>>> +    WTF::sleep(10_ms);
>>> 
>>> Should we also be waiting in the case that we already have observers?
>> 
>> That is what `waitUntilObservers` does. If we waited in there we will have this 10ms pause.
> 
> I meant more of "why are we also waiting here if we're already waiting inside `waitUntilObservers`?"

This is the first time we ever wake up the thread, and we wait here because it is created when we have a listener so it won't wait inside of `waitUntilObservers`.
If all observers unregister the thread stays alive in its while loop and will wake up when new listeners are added, those will then wait inside of `waitUntilObservers`.