Memory leak in version 2.0

[azangru]

Hi!

I have come across what seems to be a memory leak in node-canvas version 2. I've put together a very basic repro case that you can find in this repo.

Briefly, the problem manifests like this:

• Start an app that uses node-canvas v.2
• Send multiple requests to it
• Observe the memory usage. Specifically, the rss portion of process.memoryUsage is quickly increasing despite garbage collection.

For example, in my repro case, the memory usage that started with:

{"rss":72290304,"heapTotal":21008384,"heapUsed":11065680}

rose after a 1000 requests to:

{"rss":643870720,"heapTotal":17862656,"heapUsed":11048840}

(notice the rise in rss).

This memory leak is not present in the 1.x branch of node-canvas.

I tried both .pngStream() and .toBuffer() methods in my repro case (since there is an issue regarding memory leaks with pngStream). None of this helped.

If you could suggest the place in the version 2 branch that is free from this leak, I would be super grateful. I've used the master branch of node-canvas in production this winter, and it seems like there was no such bug then.

My environment:
MacOS v. 10.11.6
node v6.7.0

P.S.: I have not bisected the git history to find the exact commit that has introduced the leak, but at least at the time of this March commit memory seems to be managed fine.

[zbjornson]

Thanks for the nice repro case. I can try to look at this within the next week, but if anyone else gets to this before me, go ahead please!