> On Mar 28, 2017, at 4:23 PM, Geoffrey Garen <gga...@apple.com> wrote: > > Does the separate exceptionStackTraceLimit mean that if a developer gets a > truncated stack trace in the Web Inspector, there’s no way for the developer > to remedy that? Is that what other browsers’ developer tools do?
FireFox and Chrome show console entires with exception stack traces with 128 and 200 frames (respectively). > > Geoff > >> On Mar 28, 2017, at 4:09 PM, Mark Lam <mark....@apple.com >> <mailto:mark....@apple.com>> wrote: >> >> To follow up, I’ve implemented the change in r214289: <http://trac.webkit >> <http://trac.webkit/>.org/r214289>. Error.stackTraceLimit is now 100. I >> also implemented a separate exceptionStackTraceLimit for stack traces >> captured at the time of throwing a value (not to be confused with >> Error.stack which is captured at the time of instantiation of the Error >> object). exceptionStackTraceLimit is also limited to 100 by default. >> >> Mark >> >> >>> On Mar 17, 2017, at 1:04 PM, Mark Lam <mark....@apple.com >>> <mailto:mark....@apple.com>> wrote: >>> >>> @Geoff, my testing shows that we can do 200 frames and still perform well >>> (~1 second to console.log Error.stack). Base on what we at present, I >>> think 100 is a good round number to use as our default stackTraceLimit. >>> >>>> On Mar 17, 2017, at 11:40 AM, Maciej Stachowiak <m...@apple.com >>>> <mailto:m...@apple.com>> wrote: >>>> >>>>> >>>>> On Mar 17, 2017, at 11:09 AM, Mark Lam <mark....@apple.com >>>>> <mailto:mark....@apple.com>> wrote: >>>>> >>>>> Thanks for the reminder to back observations up with data. I was >>>>> previously running some tests that throws StackOverflowErrors a lot >>>>> (which tainted my perspective), and I made a hasty conclusion which isn’t >>>>> good. Anyway, here’s the data using an instrumented VM to take some >>>>> measurements and a simple test program that recurses forever to throw a >>>>> StackOverflowError (run on a MacPro): >>>>> >>>>> 1. For a release build of jsc shell: >>>>> Time to capture exception stack = 0.002807 sec >>>>> Number of stack frames captured = 31722 >>>>> sizeof StackFrame = 24 >>>>> total memory consumed = ~761328 bytes. >>>>> >>>>> 2. For a debug build of jsc shell: >>>>> Time to capture exception stack = 0.052107 sec >>>>> Number of stack frames captured = 31688 >>>>> sizeof StackFrame = 24 >>>>> total memory consumed = ~760512 bytes. >>>>> >>>>> So, regarding performance, I was wrong. The amount of time taken to >>>>> capture the entire JS stack each time is insignificant. >>>>> Regarding memory usage, ~760K is not so good, but maybe it’s acceptable. >>>>> >>>>> Comparing browsers with their respective inspectors open: >>>>> >>>>> 1. Chrome >>>>> number of frames captured: 10 >>>>> length of e.stack string: 824 chars >>>>> time to console.log e.stack: 0.27 seconds >>>>> >>>>> 2. Firefox >>>>> number of frames captured: 129 >>>>> length of e.stack string: 8831 chars >>>>> time to console.log e.stack: 0.93 seconds >>>>> >>>>> 3. Safari >>>>> number of frames captured: 31722 >>>>> length of e.stack string: 218821 chars >>>>> time to console.log e.stack: 50.8 seconds >>>>> >>>>> 4. Safari (with error.stack shrunk to 201 frames at time of capture to >>>>> simulate my proposal) >>>>> number of frames captured: 201 >>>>> length of e.stack string: 13868 chars >>>>> time to console.log e.stack: 1 second >>>>> >>>>> With my proposal, the experience of printing Error.stack drops from 50.8 >>>>> seconds to about 1 second. The memory used for capturing the stack also >>>>> drops from ~760K to 5K. >>>>> >>>>> I wasn’t aware of the Error.stackTraceLimit, but that does sound like a >>>>> better solution than my proposal since it gives developers the ability to >>>>> capture more stack frames if they need it. Chrome’s default >>>>> Error.stackTraceLimit appears to be 10. MS appears to support it as well >>>>> and defaults to 10 >>>>> (https://docs.microsoft.com/en-us/scripting/javascript/reference/stacktracelimit-property-error-javascript >>>>> >>>>> <https://docs.microsoft.com/en-us/scripting/javascript/reference/stacktracelimit-property-error-javascript>). >>>>> Firefox does now. >>>> >>>> Out of curiosity: Why does Firefox capture 129 frames instead of 31722 in >>>> this case? Do they have a hardcoded limit? >>> >>> Actually, my previous frame counts are a bit off. I was using >>> e.stack.split(/\r\n|\r|\n/).length as the frame count. Below, I just copy >>> the console.log dump into an editor and take the line count from there as >>> the frame count instead. The result of that string.split appears to be a >>> bit off from the actual frames printed by console.log. >>> >>> I also modified my recursing test function to console.log the re-entry >>> count on entry and this is what I saw: >>> >>> 1. Chrome >>> test reported reentry count = 10150 >>> ....split(…).length = 11 (because Chromes starts e.stack with a line >>> "RangeError: Maximum call stack size exceeded”) >>> e.stack lines according to editor = 10 frames >>> >>> 2. Firefox >>> test reported reentry count = 222044 >>> ....split(…).length = 129 (probably because there’s an extra newline in >>> there somewhere) >>> e.stack lines according to editor = 128 frames >>> >>> 3. Safari >>> test reported reentry count = 31701 >>> ....split(…).length = 31722 (I don’t know why there’s a 21 frame >>> discrepancy here. I’ll debug this later) >>> e.stack lines according to editor = ??? frames (WebInspector hangs >>> every time I try to scroll in it, let alone let me highlight and copy the >>> stack trace. So I gave up) >>> >>> Assuming the test function frame is not significantly different in size for >>> all browsers, it looks like: >>> 1. Chrome uses a much smaller stack (about 1/3 of our stack). >>> 2. Firefox uses a much larger stack (possibly the full machine stack), but >>> caps its Error.stack to just 128 frames (possibly a hardcoded limit). >>> >>> Mark >>> >>> >>>> >>>> - Maciej >>>> >>>>> >>>>> Does anyone object to us adopting Error.stackTraceLimit and setting the >>>>> default to 10 to match Chrome? >>>>> >>>>> Mark >>>>> >>>>> >>>>> >>>>>> On Mar 16, 2017, at 11:29 PM, Geoffrey Garen <gga...@apple.com >>>>>> <mailto:gga...@apple.com>> wrote: >>>>>> >>>>>> Can you be more specific about the motivation here? >>>>>> >>>>>> Do we have any motivating examples that will tell us wether time+memory >>>>>> were unacceptable before this change, or are acceptable after this >>>>>> change? >>>>>> >>>>>> In our motivating examples, does Safari use more time+memory than other >>>>>> browsers? If so, how large of a stack do other browsers capture? >>>>>> >>>>>> We already limit the size of the JavaScript stack to avoid performance >>>>>> problems like the ones you mention in many other contexts. Why is that >>>>>> limit not sufficient? >>>>>> >>>>>> Did you consider implementing Chrome’s Error.stackTraceLimit behavior? >>>>>> >>>>>> Geoff >>>>>> >>>>>>> On Mar 16, 2017, at 10:09 PM, Mark Lam <mark....@apple.com >>>>>>> <mailto:mark....@apple.com>> wrote: >>>>>>> >>>>>>> Hi folks, >>>>>>> >>>>>>> Currently, if we have an exception stack that is incredibly deep >>>>>>> (especially for a StackOverflowError), JSC may end up thrashing memory >>>>>>> just to capture the large stack trace in memory. This is bad for >>>>>>> many reasons: >>>>>>> >>>>>>> 1. the captured stack will take a lot of memory. >>>>>>> 2. capturing the stack may take a long time (due to memory thrashing) >>>>>>> and makes for a bad user experience. >>>>>>> 3. if memory availability is low, capturing such a large stack may >>>>>>> result in an OutOfMemoryError being thrown in its place. >>>>>>> The OutOfMemoryError thrown there will also have the same problem >>>>>>> with capturing such a large stack. >>>>>>> 4. most of the time, no one will look at the captured Error.stack >>>>>>> anyway. >>>>>>> >>>>>>> Since there isn’t a standard on what we really need to capture for >>>>>>> Error.stack, I propose that we limit how much stack we capture to a >>>>>>> practical size. How about an Error.stack that consists of (1) the top >>>>>>> N frames, (2) an ellipses, and (3) the bottom M frames? If the number >>>>>>> of frames on the stack at the time of capture is less or equal to than >>>>>>> N + M frames, then Error.stack will just show the whole stack with no >>>>>>> ellipses. For example, if N is 4 and M is 2, the captured stack will >>>>>>> look something like this: >>>>>>> >>>>>>> foo10001 >>>>>>> foo10000 >>>>>>> foo9999 >>>>>>> foo9998 >>>>>>> … >>>>>>> foo1 >>>>>>> foo0 >>>>>>> >>>>>>> If we pick a sufficient large number for N and M (I suggest 100 each), >>>>>>> I think this should provide sufficient context for debugging uses of >>>>>>> Error.stack, while keeping an upper bound on how much memory and time >>>>>>> we throw at capturing the exception stack. >>>>>>> >>>>>>> My plan for implementing this is: >>>>>>> 1. change Exception::finishCreation() to only capture the N and M >>>>>>> frames, plus possibly 1 ellipses placeholder in the between them. >>>>>>> 2. change all clients of Exception::stack() to be able to recognize and >>>>>>> render the ellipses. >>>>>>> >>>>>>> Does anyone object to doing this or have a compelling reason why this >>>>>>> should not be done? >>>>>>> >>>>>>> Thanks. >>>>>>> >>>>>>> Mark >>>>>>> >>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> webkit-dev mailing list >>>>>>> webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org> >>>>>>> https://lists.webkit.org/mailman/listinfo/webkit-dev >>>>>>> <https://lists.webkit.org/mailman/listinfo/webkit-dev> >>>>>> >>>>> >>>>> _______________________________________________ >>>>> webkit-dev mailing list >>>>> webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org> >>>>> https://lists.webkit.org/mailman/listinfo/webkit-dev >>>>> <https://lists.webkit.org/mailman/listinfo/webkit-dev> >>> _______________________________________________ >>> webkit-dev mailing list >>> webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org> >>> https://lists.webkit.org/mailman/listinfo/webkit-dev >>> <https://lists.webkit.org/mailman/listinfo/webkit-dev> >> _______________________________________________ >> webkit-dev mailing list >> webkit-dev@lists.webkit.org <mailto:webkit-dev@lists.webkit.org> >> https://lists.webkit.org/mailman/listinfo/webkit-dev > > _______________________________________________ > webkit-dev mailing list > webkit-dev@lists.webkit.org > https://lists.webkit.org/mailman/listinfo/webkit-dev
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