On Tue, 29 Aug 2023 20:51:56 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::DROP_METHOD_INFO` enum that requests to >> drop the method information. If no method information is needed, a >> `StackWalker` with `DROP_METHOD_INFO` >> can be used instead and such stack walker will save the overhead of >> extracting the method information >> and the memory used for the stack walking. >> >> New factory methods to take a parameter to specify the kind of stack walker >> to be created are defined. >> This 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 function >> for traversing >> `StackFrame`s. >> >> For example: to find the first caller filtering a known list of >> implementation class, >> existing code can create a stack walker instance with `DROP_METHOD_INFO` >> option: >> >> >> StackWalker walker = StackWalker.getInstance(Option.DROP_METHOD_INFO, >> Option.RETAIN_CLASS_REFERENCE); >> Optional<Class<?>> callerClass = walker.walk(s -> >> s.map(StackFrame::getDeclaringClass) >> .filter(Predicate.not(implClasses::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. >> >> #### Javadoc & specdiff >> >> https://cr.openjdk.org/~mchung/api/java.base/java/lang/StackWalker.html >> https://cr.openjdk.org/~mchung/jdk22/specdiff/overview-summary.html >> >> #### Alternatives Considered >> One alternative 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 >> >> A `StackWalker` configured with `DROP_METHOD_INFO` ... > > Mandy Chung has updated the pull request incrementally with three additional > commits since the last revision: > > - update mode to be int rather than long > - update tests > - Review feedback on javadoc src/java.base/share/classes/java/lang/StackStreamFactory.java line 694: > 692: // no method information is available; should just filter > 693: // "Continuation::yield0". > 694: return classFrames[index].declaringClass() == > Continuation.class; Is that going to be an issue if by chance the frame is some other method on continuation? Could that comment be clarified a bit? I am not sure what is meant by `should just filter "Continuation::yield0"`; Does it mean: that's what we should do, but we can't, so we filter any method on `Continuation` instead? Or does it mean: the only method we expect here if declaringClass is `Continuation` is `yield0`, so the line below should only filter out `Continuation::yield0`? ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/15370#discussion_r1310422354
