On Tue, 22 Aug 2023 19:01:53 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 `StackWalker.Kind` enum to specify the information >> that a stack walker >> collects. If no method information is needed, a `StackWalker` of >> `CLASS_INFO` can be used >> instead and such 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 >> >> 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 call `StackWalker::getInstance(CLASS_INFO, ...)` to create >> a stack walker instance: >> >> >> StackWalker walker = StackWalker.getInstance(Kind.CLASS_INFO, >> Option.RETAIN_CLASS_REFERENCE); >> 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. >> >> #### 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. >> >> Another alternative is to add a new `NO_METHOD_INFO` option. Similar to the >> proposed API, >>... > > Mandy Chung has updated the pull request with a new target base due to a > merge or a rebase. The pull request now contains 16 commits: > > - Replace NO_METHOD_INFO option with StackWalker.Kind enums > - Merge branch 'master' of https://github.com/openjdk/jdk into > stackwalker-class > - clean up > - fix trailing whitespace > - Merge branch 'master' of https://github.com/openjdk/jdk into > stackwalker-class > - Update LocalLongHelper.java > - clean up > - Merge branch 'master' of https://github.com/openjdk/jdk into > stackwalker-class > - Add StackWalker.Option.NO_METHOD_INFO > - Merge branch 'master' of https://github.com/openjdk/jdk into > stackwalker-class > - ... and 6 more: https://git.openjdk.org/jdk/compare/ce1ded1a...434d90cb src/java.base/share/classes/java/lang/StackFrameInfo.java line 38: > 36: SharedSecrets.getJavaLangInvokeAccess(); > 37: > 38: private final boolean retainClassRef; Shouldn't `private final boolean retainClassRef` move to ClassFrameInfo? Isn't it strange that CLASS_INFO still implies RETAIN_CLASS_REFERENCE? ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/15370#discussion_r1303378176
