这是Xpath评估中的Chrome错误吗

Question

Open this page: http://sunnah.com/abudawud/2

And run this simple xpath search query in the console. Then the browser tab crashes

for(var k=0, kl=2000; k < kl; k++){
    console.log(k);
    var xpathResult = document.evaluate("//div[@class='hello']", document, null, XPathResult.ANY_TYPE, null);
}

On chrome Version 46.0.2490.80 (64-bit) on Macbook Pro, OSX 10.10.5

Unfortunately i have to run the xpath on this page a couple of thousands of time to search for different elements. So i can't get away with not doing that many calls to evaluate.

The crash is dependent on the xpath term. for some terms it crashes and for some others it does not.

It fails consistently on the same count so it makes me think it is not a timing issue or garbage collection issue.

I am not getting any error codes so I am not sure where else to look.

Update After further investigation we believe this is a legitimate Chrome bug or at least not very good way of releasing memory. What happens is that if your xpath starts with / or // then the search context is expanded to all of DOM and for some reason chrome keeps the DOM or some other intermediary object in memory. If the xpath does starts with relative path like (div/p) and the search scope ( second argument) is set to portions of the DOM the memory consumption is much more reasonable and there is no crash. Thanks to @JLRishe for several hints that were very helpful to get to this conclusion.

Update2 I filed a bug on chromium. But after a few months they rejected the bug as wont-fix. I managed to work around it for the time being.

Answer 1

If I run your code on that page and watch Task Manager, I can see Chrome's working set increase to about 3.3 GB before it eventually crashes after about 1300 iterations.

Each XPath query is causing Chrome to allocate memory for the results and any operation involved in obtaining them, but it seems like it is not releasing any of the allocated memory because you are not releasing control of the thread.

I have found that the working set levels out at 1.65 GB and the operation finishes without crashing if I do this:

var k = 0;
var intv = setInterval(function () {
    console.log(k);
    var xpathResult = document.evaluate("//div[@class='hello']", document, null, XPathResult.ANY_TYPE, null);
    k += 1;
    if (k >= 2000) {
        clearInterval(intv);
    }
}, 0);

so something like that might be a possible solution.

This is still using considerable system resources, and this isn't even including any values you might be storing in the course of your operation. I encourage you to seek out a smarter approach that doesn't require running quite so many XPath queries.