On Thu, 24 Aug 2023 18:44:14 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 incrementally with one additional > commit since the last revision: > > review feedback and javadoc clean up > StackWalkers would be configured along two different axes (Kind and Options). This is intentional. `Kind` is not the best name but it describes what information a stack walker collects from each stack frame. > It changes the mental model, in that all StackWalkers would now be divided > into two Kinds. I feel like this bleeds the implementation into the API a bit. Although this RFE is motivated by an optimized way to walk the stack, each method has a declaring class. In the current implementation, it has an internal way to collect the live locals and operands on the stack (`LOCALS_AND_OPERANDS`). That fits into the third type to be collected from each frame. If that were supported, it would belong to the new enum type. > The existing Option enum already provides a way to configure which frames are > walked, and what information to include in those frames. I think adding a new > Option value fits better. > > It's true that compatibility dictates that the default behavior be to include > method info, so the new option must omit method info. If the NO_METHOD_INFO > is disliked, perhaps a better name can be found - SKIP_METHOD_INFO or > OMIT_METHOD_INFO? In fact it's not so much constrained by the default behavior. I wasn't completely happy with adding `NO_METHOD_INFO` to the options but could live with it. When I reconsidered, I like separating this from `Option` as it specifies what information to be collected from each frame whereas `Option` controls everything else such as what frames to be filtered for better categorization. I updated the javadoc. Maybe it helps? https://cr.openjdk.org/~mchung/api/java.base/java/lang/StackWalker.html https://cr.openjdk.org/~mchung/jdk22/specdiff/overview-summary.html ------------- PR Comment: https://git.openjdk.org/jdk/pull/15370#issuecomment-1692474762
