SparseHistogram Leakage in Cronet

[逸尘]

Hi,

I am a user of Cronet. I found some memory leakage during my stability test. 

I checked the code, and I think the root cause is that the global StatisticsRecorder g_statistics_recorder_ is not initialized. However, I also noticed that there is a comment: ''As per crbug.com/79322 the histograms are intentionally leaked, so we need to annotate them". It seems to me the leakage under the uninitialized situation is by design.

I am curious about why it is intentionally to leak? Is it harmless? 

Could you please kindly help to explain?

Thanks in advance.

Best Wishes,

JIANG Yichen 

[Alexei Svitkine]

+mef

You're correct that StatisticsRecorder::Initialize() must be called to prevent leaks. There should be a single instance of a Histogram object for each histogram name - that instance is meant to be leaked (meaning we don't free it at shut down) - but if you don't initialize the StatisticsRecorder then the code will end up creating an instance of the histogram each time you log a histogram and leak those - which would be quite bad.

Looking at the Cronet code itself, it looks like there is a call to StatisticsRecorder::Initialize() - but seems it's done too late - in GetHistogramDeltas() - which would be called only if the histograms are serialized to be uploaded. This is too late because by that point, a lot of histograms could have already been logged/leaked. Ideally, this should be done during Cronet initialization.

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[逸尘]

Alexei, 

Thank you so much for the detailed explanation.  

在 2017年3月31日星期五 UTC+8下午11:06:03，Alexei Svitkine写道：

[Helen Li]

Thanks. I filed https://bugs.chromium.org/p/chromium/issues/detail?id=707836 to track this on Cronet side.

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