On Wed, 5 Jul 2023 11:45:59 GMT, Volker Simonis <simo...@openjdk.org> wrote:
> As the included jtreg test demonstrates, `StackWalker.getCallerClass()` can > throw an `UnsupportedOperationException` if called reflectively. Currently > this only happens if we invoke `StackWalker.getCallerClass()` recursively > reflectively, but this issue will become more prominent once we fix > [JDK-8285447](https://bugs.openjdk.org/browse/JDK-8285447). The gory details > follow below: > > The protocol between the Java API and the JVM for > `StackWalker.getCallerClass()/walk()` is as follows: > - On the Java side, `StackWalker` calls into `StackStreamFactory` for the > real work. > - For `StackWalker.getCallerClass()` `StackStreamFactory` basically creates a > `Class[]` which will be passed down and filled in the JVM. For > `StackWalker.walk()` it will normally be a `StackFrameInfo[]` (or a > `LiveStackFrameInfo[]` if the internal `ExtendedOption.LOCALS_AND_OPERANDS` > option was used). > - The default size of this arrays is currently > `StackStreamFactory.SMALL_BATCH` which is 8 (but see > [JDK-8285447](https://bugs.openjdk.org/browse/JDK-8285447)). > - `StackStreamFactory` than calls `AbstractStackWalker.callStackWalk()` which > is a natively implemented in the VM by `JVM_CallStackWalk()`. > - `JVM_CallStackWalk()` calls `StackWalk::walk()` which calls > `StackWalk::fetchFirstBatch()` which calls `StackWalk::fill_in_frames()` > which walks the stack and fills in the available class/stackframe slots in > the passed in array until the array is full or there are no more stack frames, > - Once `StackWalk::fill_in_frames()` returns, `StackWalk::fetchFirstBatch()` > calls back to Java by invoking `AbstractStackWalker::doStackWalk()` to > consume the result. > - `AbstractStackWalker::doStackWalk()` calls `consumeFrames()` (which is > overridden depending on whether we initially called `getCallerClass()` or > `walk()`) which consumes the frames until it either finishes (e.g. finds the > caller class) or until there are no more frames. > - In the latter case `consumeFrames()` will call into the the VM again by > calling `AbstractStackWalker.fetchStackFrames()` to fetch additional frames > from the stack. > - `AbstractStackWalker.fetchStackFrames()` is implemented by > `JVM_MoreStackWalk()` which calls `StackWalk::fetchNextBatch()` which calls > `StackWalk::fill_in_frames()` (the same method that already fetched the > initial batch of frames). > > Following is a stacktrace of what I've explained so far: > > Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native > code) > V [libjvm.so+0x143a96a] StackWalk::fill_in_frames... This pull request has been closed without being integrated. ------------- PR: https://git.openjdk.org/jdk/pull/14773
