On Sat, 18 Jun 2022 03:59:44 GMT, Serguei Spitsyn <sspit...@openjdk.org> wrote:
> The JVMTI SetLocalXXX requires the target virtual thread suspended at a > breakpoint or single step event. > > This is the relevant statement from the "Local Variable" section: > > `The SetLocalXXX functions may be used to set the value of a local variable > in the topmost frame of a virtual thread suspended at a breakpoint or single > step event. > ` > This fix is to return the JVMTI_ERROR_OPAQUE_FRAME in cases when the target > thread is not at a breakpoint or single step event. In this case the assert > described in the bug report is avoided: > > > open/src/hotspot/share/runtime/vframe.cpp:300 > # assert(stack_chunk() == __null) failed: Not supported for heap frames > > Also, this is an analysis from Ron: > > The problem occurs because the thread is suspended at a safepoint poll on > return in the oldest thawed frame. The safepoint happens after the frame is > popped but before it returns to the return barrier, thawing the caller (and > so the stack looks as if we're in enterSpecial). In that case the virtual > thread's topmost frame is still frozen on the heap, even though it is mounted. > > However, the spec says that a set local operation should succeed for the > topmost frame of a mounted virtual thread only if the thread is suspended *at > a breakpoint or a single-step event*, and I don't think we can stop at that > safepoint in that case. > > If so, the fix is simple: if we're trying to set, even if the virtual thread > is mounted and the depth is zero, if the frame is a heap frame, we should > return an OPAQUE_FRAME error. The test should be changed as well to accept > such an error if the thread is suspended not at a breakpoint/single-step. > > > Changes `GetSetLocalTest` test are taken from the repo-loom repository. It > was an update from Leonid which is needed to reproduce this problem. > > The fix was tested with thousands of runs of the `GetSetLocalTest` on Linux, > Windows and MacOs. > > Will also submit nsk.jvmti and nsk.jdi test runs on mach5. This pull request has now been integrated. Changeset: 4c9ea7e6 Author: Serguei Spitsyn <sspit...@openjdk.org> URL: https://git.openjdk.org/jdk19/commit/4c9ea7e66aaf99f42ee2df0b17c6586f57019a19 Stats: 44 lines in 4 files changed: 23 ins; 5 del; 16 mod 8286580: serviceability/jvmti/vthread/GetSetLocalTest failed with assert: Not supported for heap frames Reviewed-by: lmesnik, rpressler, cjplummer ------------- PR: https://git.openjdk.org/jdk19/pull/42
