On Mon, 21 Aug 2023 21:10:36 GMT, Mandy Chung <mch...@openjdk.org> wrote:
>> 8268829: Provide an optimized way to walk the stack with Class object only >> >> `StackWalker::walk` creates one `StackFrame` per frame and the current >> implementation >> allocates one `StackFrameInfo` and one `MemberName` objects per frame. Some >> frameworks >> like logging may only interest in the Class object but not the method name >> nor the BCI, >> for example, filters out its implementation classes to find the caller >> class. It's >> similar to `StackWalker::getCallerClass` but allows a predicate to filter >> out the element. >> >> This PR proposes to add `Option.NO_METHOD_INFO` new stack walking option. >> If no method information is needed, this option can be used such that the >> stack walker will save the overhead (1) to extract the method information >> and (2) the memory used for the stack walking. In addition, this can also >> fix >> >> - [8311500](https://bugs.openjdk.org/browse/JDK-8311500): >> StackWalker.getCallerClass() throws UOE if invoked reflectively >> >> Adding `NO_METHOD_TIME` option provides a simple way for existing code, >> for example logging frameworks, to take advantage of this enhancement with >> the least change as it can keep the existing implementation in traversing >> `StackFrame`s. >> >> For example: to find the first caller filtering a known list of >> implementation class, >> existing code can just add `NO_METHOD_INFO` in the call to >> `StackWalker::getInstance` >> to create a stack walker instance: >> >> >> StackWalker walker = >> StackWalker.getInstance(Option.RETAIN_CLASS_REFERENCE, NO_METHOD_INFO); >> Optional<Class<?>> callerClass = walker.walk(s -> >> s.map(StackFrame::getDeclaringClass) >> .filter(interestingClasses::contains) >> .findFirst()); >> >> >> If method information is accessed on the `StackFrame`s produced by this >> stack walker such as >> `StackFrame::getMethodName`, then `UnsupportedOperationException` will be >> thrown. >> >> The alternative considered is to provide a new API: >> `<T> T walkClass(Function<? super Stream<Class<?>, ? extends T> function)` >> >> In this case, the caller would need to pass a function that takes a stream >> of `Class` object instead of `StackFrame`. Existing code would have to >> modify calls to the `walk` method to `walkClass` and the function body. >> >> ### Implementation Details >> >> If `NO_METHOD_NAME` is set, the implementation creates `ClassFrameInfo[]` >> buffer that is filled by the VM during stack walking. `ClassFrameInfo` >> holds the >> Class instance plus `flag... > > Mandy Chung has updated the pull request incrementally with one additional > commit since the last revision: > > clean up @vidmik gave the feedback about the name of the option `NO_METHOD_INFO`, generally preferred a positive word. I do agree. One option is to introduce `enum Kind { CLASS_INFO, METHOD_INFO}` instead of `NO_METHOD_INFO` and new factory methods `getInstance(Kind kind, Option... option)`. `getInstance()` is equivalent to `getInstance(METHOD_INFO)`. To collect class only, do getInstance(CLASS_INFO); getInstance(CLASS_INFO, RETAIN_CLASS_REFERENCE); I think a new enum is a cleaner way to specify what information to collect. Any feedback/thought before I update this? ------------- PR Comment: https://git.openjdk.org/jdk/pull/15370#issuecomment-1687140453
