On Wed, 2 Sep 2026 20:11:48 GMT, Shiv Shah <[email protected]> wrote: > When a virtual thread suspended at a breakpoint gets unmounted and mounted > again only the top frame is thawed. The caller stays frozen in the stack > chunk and the popped frame returns into the continuation return barrier. The > interpreter's popframe entry treats that return address like a deoptimized > caller, preserves the arguments, sets the reexecution bit and returns. The > barrier then thawed the caller as a plain return. Arguments and bit left > behind, no reexecution of the invoke, run() went on with a zero result. > > Thaw finishes it now. An interpreted caller gets the preserved arguments back > on its expression stack and its return slot is patched to the interpreter > deopt entry after push_return_frame, the x86 deopt entry reloads rsp from > last_sp for that, aarch64 already does. A compiled caller frozen in the chunk > is deoptimized from UpdateForPopTopFrameClosure::doit the same way > set_frame_pop does it. Thaw leaves the arguments alone in that case and > unpack_on_stack puts them back. A frozen compiled frame being popped stays > opaque. > > A linkTo caller needs one more thing. The linker consumed the trailing > MemberName before the target ran and the preserved arguments are sized by the > target, so the MemberName is not among them. Thaw takes it from the caller's > local 0 the way the interpreter's popframe entry does, the lookup from > member_name_arg_or_null moved into a plain helper both can call. The > arguments go one slot up and the MemberName goes back on top. > > popframes002 runs popframes001 on a virtual thread with the join Chris > Plummer wrote enabled by a property in the debuggee. It unmounts the tested > thread before the breakpoint so the caller is frozen when popped, and run() > is excluded from compilation so this stays the interpreted case. popframes003 > is the compiled caller case, -Xcomp with the breakpoint in a separate stop() > so testedMethod keeps its compiled frame and run() stays frozen, the debugger > pops frame 1 and the debuggee checks with WhiteBox that run() and > testedMethod are compiled and that testedMethod ran twice. > -XX:+PreserveFramePointer keeps the thaw on the slow path. Both fail on > master without the hotspot change. popframes001 itself runs the plain case as > before and is off the virtual problem list. If separate copies of the > debugger and debuggee are preferred over the properties that is easy to > change. PopFrameMethodNameInvariantTest got an unmount mode, the same > linkToStatic pop on a virtual thread that sleeps before the breakpoint so its ca...
src/hotspot/share/runtime/continuationFreezeThaw.cpp line 3100: > 3098: // without the callee's arguments, so put the preserved arguments > back on its > 3099: // expression stack and resume at the invoke instead of after it, like > 3100: // vframeArrayElement::unpack_on_stack does for a deoptimized caller. Nit: The line 3094 tells about "the barrier". In fact, it is still a little bit confusing because I normally start thinking about the GC barriers. The comment has to be more clear that this is about the "return barrier" even though it tells: "A frame popped by JVMTI PopFrame **returned** through the barrier". ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/32661#discussion_r4110987685
