> 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...
Mandy Chung has updated the pull request incrementally with two additional commits since the last revision: - Generify StackFrameInfo to replace duplicated code - replace href with @linkplain ------------- Changes: - all: https://git.openjdk.org/jdk/pull/15370/files - new: https://git.openjdk.org/jdk/pull/15370/files/111661bc..a623b9dc Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=15370&range=09 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15370&range=08-09 Stats: 146 lines in 2 files changed: 22 ins; 97 del; 27 mod Patch: https://git.openjdk.org/jdk/pull/15370.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/15370/head:pull/15370 PR: https://git.openjdk.org/jdk/pull/15370
