On Mon, 21 Aug 2023 20:07:20 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` option creates > `ClassFrameInfo[]` > buffer that is filled by the VM during stack walking. `Sta... This pull request has now been integrated. Changeset: 111ecdba Author: Mandy Chung <mch...@openjdk.org> URL: https://git.openjdk.org/jdk/commit/111ecdbaf58e5c0b3a64e0eca8a291df295e71b0 Stats: 1340 lines in 34 files changed: 718 ins; 358 del; 264 mod 8268829: Provide an optimized way to walk the stack with Class object only 8210375: StackWalker::getCallerClass throws UnsupportedOperationException Reviewed-by: coleenp, dfuchs, bchristi ------------- PR: https://git.openjdk.org/jdk/pull/15370
