On Thu, 7 Sep 2023 19:27:14 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 `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 one additional > commit since the last revision: > > Fix @Param due to the rename from default to class+method The value of flags can only be 0 or 0x08000000, so flags & MEMBER_INFO_FLAGS in isHidden and isCallerSensitive methods are always false ClassFrameInfo(StackWalker walker) { this.flags = walker.retainClassRef ? RETAIN_CLASS_REF_BIT : 0; } private static final int MEMBER_INFO_FLAGS = 0x00FFFFFF; private static final int RETAIN_CLASS_REF_BIT = 0x08000000; // retainClassRef The flags field is only assigned in the ClassFrameInfo constructor, so flags can be set to final, and the value here will only be 0 or RETAIN_CLASS_REF_BIT (0x08000000). So `flags & MEMBER_INFO_FLAGS` in the following code is always false boolean isCallerSensitive() { return JLIA.isCallerSensitive(flags & MEMBER_INFO_FLAGS); } boolean isHidden() { return JLIA.isHiddenMember(flags & MEMBER_INFO_FLAGS); } ------------- PR Comment: https://git.openjdk.org/jdk/pull/15370#issuecomment-2846210254
