> Implements the native profiler hook for unbiased stack-traces, as described > in [JEP draft: Native Profiler Hook for Unbiased Stack Traces > (Experimental)](https://openjdk.org/jeps/8380294). > > New JVMTI extension function: `RequestStackTrace(jvmtiEnv*, jthread*, void* > ucontext, jlong user_data)` - async-signal-safe request for a stack trace. > For the current thread, `ucontext` may be `nullptr` or the signal-handler > `ucontext`. For another thread, the thread must be suspended for the duration > of the call and `ucontext` must be captured during that suspension; otherwise > the VM may crash. Returns `JVMTI_ERROR_NONE`, `JVMTI_ERROR_INVALID_THREAD`, > or `JVMTI_ERROR_NOT_AVAILABLE`. Requests may be silently dropped (queue full, > wrong thread state, rate-limited). > > New experimental JFR event `StackTraceRequest` with fields `stackTrace`, > `eventThread`, `userData`, `failed`, `biased`. Enabled in `profile.jfc`, not > in `default.jfc` (the rate is controlled by the external agent, so default-on > would expose users to unbounded overhead). > > The machinery gets enabled/disabled whenever the event `StackTraceRequest` > gets enabled/disabled. > > Refactoring: The stack-walker request machinery from JEP 509 (CPU-time > profiler) is generalized into a callback-based API (`JfrStackWalkerCallback`) > used by both the CPU-time profiler and the new JVMTI hook. Shared pieces: the > per-thread signal-safe request queue, the enqueue/dequeue lock state machine, > and the native stack-walker thread that processes requests for in-native > threads. Two callback implementations remain: one for > CPUTimeSample/empty/lost events, one for StackTraceRequest. > > Non-goals (per the JEP): Native frames are not reported; this is a follow-up. > > Platform support: Linux and MacOS, or more generally POSIX. Windows support > can be a follow-up, if ucontext is interpreted as WPA context. > > Testing: > > Several tests have been added that verify the new functionality. > > - [x] jdk_jfr > - [x] serviceability/jvmti > > --------- > - [x] I confirm that I make this contribution in accordance with the [OpenJDK > Interim AI Policy](https://openjdk.org/legal/ai).
Roman Kennke has updated the pull request incrementally with three additional commits since the last revision: - Fold JfrStackWalker hooks into Jfr facade, drop unused walker API, and minimize changes to existing JFR code - Bail out of compute_top_frame when no frame is found above the sampled sp - Reuse JFR sample-request building and top-frame computation in JfrStackWalker, also picks up NEEDS_STACK_REPAIR handling, which the copy lacked ------------- Changes: - all: https://git.openjdk.org/jdk/pull/31059/files - new: https://git.openjdk.org/jdk/pull/31059/files/84a9ea59..eafaa210 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=31059&range=04 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=31059&range=03-04 Stats: 994 lines in 24 files changed: 203 ins; 730 del; 61 mod Patch: https://git.openjdk.org/jdk/pull/31059.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/31059/head:pull/31059 PR: https://git.openjdk.org/jdk/pull/31059
