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?
Geoff > On Mar 28, 2017, at 4:09 PM, Mark Lam <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 > https://lists.webkit.org/mailman/listinfo/webkit-dev
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