CODEWITHSUNDEEP
javascriptmemory-leaksgarbage-collectiongoogle-chrome-devtools
Cyril MacIsaac
Cyril MacIsaac

Reputation: 160

Can I get the GC'd memory from dev tools?

I have a large app thata I am debugging. I have noticed a saw-tooth memory pattern that indicates that there is frequent GC going on.

In an effort to debug this I am trying to find the contents of the memory that is being GC'd. Is this possible in chrome with dev tools? I know I can take heap snapshots, but how do I guarantee that this happens immediately before and after a GC? I know I can trigger a heap snapshot from code, but same question.

Upvotes: 4

Views: 631

Answers (2)

loislo
loislo

Reputation: 14119

With Record Heap Allocation profile type you can get the information about allocated objects.

You need to enable "Record heap allocation stack traces" option in the DevTools settings. See screenshot.

Settings screenshot

After that you need to record "Record heap allocations" snapshot type. The recording process may significantly slow down the page because DevTools scans the js stack each time when the page allocates an object. As a result you will get the snapshot which has the information about allocations. In many cases DevTools can detect the class name of the objects. See screenshot.

enter image description here

In the snapshot you need to select Allocation view.

I think the information in the grid could help you to solve your problem. In the screenshot you can see that there were 41k allocations for a class but only 12k of them still alive. So 29k objects were the garbage. And even if you don't see the name of the object you could jump into sources where the objects were allocated.

Upvotes: 1

Konrad Dzwinel
Konrad Dzwinel

Reputation: 37903

Insight into the garbage collection is not available yet in the DevTools. I have requested this feature some time ago though. You can "star it" to indicate that you would also like to have it.

As for the snapshots, you won't be able to use them for your purpose. Before each snapshot is made all garbage is collected.

Are "dead" (unreachable) objects included in snapshots?

No. Only reachable objects are included in snapshots. Also, taking a snapshot always starts with doing a GC.

source

Your best shot is to record heap allocations ("Profiles" > "Record Heap Allocations") and use memory snapshots to understand what objects are being created by the app. With that knowledge, you can try identifying shortly lived objects (that cause the sawtooth pattern).

BTW, if you are using requestAnimationFrame, you should know that it's causing saw tooth pattern by itself.

Upvotes: 1

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