Implement sys/thread/vibix.rs and sys/sync/vibix/ (futex-based) in std fork

[dburkart]

Summary

• Implements sys/thread/vibix.rs: Thread::new() via clone with mmap'd stack, Thread::join() via futex wait on CHILD_CLEARTID, yield_now(), sleep(), available_parallelism() (returns 1), set_name() (stub)
• Adds futex PAL module (sys/pal/vibix/futex.rs) providing Futex/SmallFutex types and futex_wait/futex_wake/futex_wake_all for the sync primitives
• Wires target_os = "vibix" into the futex branches of Mutex, Condvar, RwLock, Once, and Parker cfg_select! dispatchers
• Adds vibix_abi::futex and vibix_abi::thread modules with syscall wrappers for clone, futex, sched_yield, nanosleep, gettid, set_tid_address

This completes Phase 3 and unblocks multi-threaded std programs on vibix.

Test plan

• cargo xtask build -- kernel builds cleanly
• std fork builds: __CARGO_TESTS_ONLY_SRC_ROOT=library cargo +nightly build -Z build-std=std,core,alloc,panic_abort -Z json-target-spec --target x86_64-unknown-vibix.json (only unrelated profiler_builtins failure from missing LLVM source)

Closes #857

🤖 Generated with Claude Code

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 5e2b525a-2504-4fcf-995f-beb74c55ba27

📥 Commits

Reviewing files that changed from the base of the PR and between 1e5dd8b and ae9295b.

📒 Files selected for processing (12)

• library/std/src/sys/pal/vibix/futex.rs
• library/std/src/sys/pal/vibix/mod.rs
• library/std/src/sys/sync/condvar/mod.rs
• library/std/src/sys/sync/mutex/mod.rs
• library/std/src/sys/sync/once/mod.rs
• library/std/src/sys/sync/rwlock/mod.rs
• library/std/src/sys/sync/thread_parking/mod.rs
• library/std/src/sys/thread/mod.rs
• library/std/src/sys/thread/vibix.rs
• userspace/vibix_abi/src/futex.rs
• userspace/vibix_abi/src/lib.rs
• userspace/vibix_abi/src/thread.rs

📝 Walkthrough

Walkthrough

This pull request adds futex and thread support for the Vibix platform to Rust's standard library. It introduces low-level futex syscall wrappers in userspace ABI, implements a Vibix-specific thread spawning and joining mechanism via Linux-style clone and futex, and wires the Vibix target into the existing futex-based implementations of Mutex, Condvar, RwLock, Once, and thread parking within std's platform-selection macros.

Changes

Vibix Threading and Futex Integration

Layer / File(s)	Summary
ABI Syscall Wrappers userspace/vibix_abi/src/futex.rs, userspace/vibix_abi/src/thread.rs, userspace/vibix_abi/src/lib.rs	Low-level futex syscall wrappers (futex_wait, futex_wake) and Linux-style thread syscalls (clone, sched_yield, nanosleep, gettid, set_tid_address, join_thread) are added to the Vibix ABI crate, along with clone flag constants and Timespec struct.
PAL Futex Module library/std/src/sys/pal/vibix/futex.rs, library/std/src/sys/pal/vibix/mod.rs	Futex type aliases (Futex, SmallFutex) and public futex operations (futex_wait, futex_wake, futex_wake_all) are implemented in the std PAL, wrapping the ABI syscall wrappers and providing a uniform interface for sync primitives.
PAL Thread Implementation library/std/src/sys/thread/vibix.rs, library/std/src/sys/thread/mod.rs	Vibix thread implementation via clone syscall with manual stack allocation (mmap), shared ThreadData for join synchronization via futex, a child trampoline function, and helper functions (available_parallelism, current_os_id, yield_now, set_name, sleep) are added and wired into the thread module selector.
Sync Primitives Wiring library/std/src/sys/sync/{condvar,mutex,once,rwlock,thread_parking}/mod.rs	target_os = "vibix" is added to the cfg_select! branches that route Mutex, Condvar, RwLock, Once, and Parker to their futex-based implementations.

Sequence Diagram

sequenceDiagram
    actor UserCode
    participant std_thread
    participant vibix_thread
    participant vibix_abi
    participant Kernel

    UserCode->>std_thread: spawn(closure)
    std_thread->>vibix_thread: Thread::new(stack_size, init)
    vibix_thread->>vibix_thread: allocate mmap stack
    vibix_thread->>vibix_thread: allocate ThreadData + store on stack
    vibix_thread->>vibix_abi: clone(flags, stack, child_tid)
    vibix_abi->>Kernel: SYS_CLONE
    Kernel-->>vibix_abi: child_tid
    vibix_abi-->>vibix_thread: parent returns Thread, child starts trampoline
    vibix_thread->>vibix_thread: thread_trampoline() runs closure, cleanup
    vibix_thread->>Kernel: SYS_EXIT (child only)
    
    UserCode->>std_thread: join()
    std_thread->>vibix_thread: Thread::join()
    vibix_thread->>vibix_thread: loop: read child_tid atomic
    vibix_thread->>vibix_abi: futex_wait on child_tid
    vibix_abi->>Kernel: SYS_FUTEX (FUTEX_WAIT)
    Kernel-->>vibix_abi: woken when child calls SYS_EXIT
    vibix_thread->>vibix_thread: unmap stack, drop ThreadData
    vibix_thread-->>UserCode: join() returns

Loading

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

The changes introduce multiple layers of interdependent functionality: low-level syscall wrappers, complex memory management with manual stack allocation and mmap, inline assembly for clone, futex-based synchronization primitives, and a trampoline function for thread initialization. While most changes are straightforward cfg routing, the vibix.rs thread implementation contains dense logic covering stack alignment, ThreadData lifecycle, raw pointer manipulation, and syscall error handling that requires careful review.

Possibly related issues

• Implement sys/thread/vibix.rs and sys/sync/vibix/ (futex-based) in std fork #857: Directly addresses the work requested (implement sys/thread/vibix.rs and futex-based sync primitives with cfg wiring) to complete Phase 3 of RFC 0009 — Rust std on Vibix.
• Implement Phase 3 syscalls: clone, futex, sched_yield, set_tid_address, gettid, getppid #856: Overlaps with the kernel-side syscall implementations for clone, futex, set_tid_address, and gettid that this userland code depends on.
• Create vibix_abi crate with syscall macro, GlobalAlloc, errno, and stdio #849: The new userspace/vibix_abi modules (futex.rs and thread.rs) directly build on the vibix_abi crate infrastructure.
• Implement Phase 2 syscalls: rename, renameat, pread64, pwrite64, nanosleep, uname #853: The new sleep implementation uses the sys_nanosleep syscall wrapper, aligning with that feature request.

Possibly related PRs

• dburkart/vibix#865: Implements the kernel-side counterpart syscalls (sys_futex, sys_clone, set_tid_address, gettid, sched_yield) that this PR's userland code invokes.
• dburkart/vibix#862: Establishes the vibix_abi crate and syscall infrastructure that the new futex and thread modules extend.

Poem

🐰 A rabbit's ode to threading swift,
With clone syscalls and futex gift,
Stack mmap'd with care so deep,
Threads awake from futex sleep,
Vibix now can spawn and join! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: implementing thread and sync support for vibix using futex-based primitives in the std fork.
Description check	✅ Passed	The description is related to the changeset, providing a detailed summary of the implementations added and the test plan results.
Linked Issues check	✅ Passed	The PR meets all primary objectives from #857: implements Thread::new/join, futex PAL module, wires vibix into sync primitive dispatchers, adds syscall wrappers, and provides evidence of successful builds.
Out of Scope Changes check	✅ Passed	All changes are scoped to the stated objectives: thread implementation, futex PAL, sync primitive wiring, and ABI syscall wrappers. No unrelated changes detected.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch m857-std-thread-sync

---

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

library/std/src/sys/thread/vibix.rs (1)

198-206: 💤 Low value

Consider using a cleaner type conversion.

The pointer cast from AtomicU32 to Atomic<u32> works but is fragile. If the internal futex API changes to use a different type, this could break silently.

Consider whether the futex API could be extended to accept &AtomicU32 directly, or add a type alias/newtype to make this relationship explicit.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@library/std/src/sys/thread/vibix.rs` around lines 198 - 206, The current code
performs an unsafe pointer cast from AtomicU32 to
crate::sync::atomic::Atomic<u32> when calling futex_wait, which is fragile;
change the API or call site to avoid this raw cast by either (A) updating
crate::sys::futex::futex_wait to accept &AtomicU32 directly, or (B) introduce a
clear type alias/newtype that maps crate::sync::atomic::Atomic<u32> to AtomicU32
and use that alias at the call site, then pass &data.child_tid without the
unsafe pointer trick; update the futex_wait signature and all callers
(futex_wait) or add the alias/newtype and a safe conversion impl to replace the
unsafe cast around data.child_tid.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@library/std/src/sys/pal/vibix/futex.rs`:
- Around line 40-47: The current code turns oversized durations into None (via
try_into().ok()?), causing timeout_ptr to become 0 and thus turning a finite
timeout into an unbounded wait; change the conversion so Timespec is always
constructed and large durations are clamped instead of dropping to None: replace
the try_into().ok()? path in the timeout -> Timespec creation with a
saturating/clamping conversion (e.g., map dur.as_secs() to i64::MAX on overflow)
and set tv_nsec from dur.subsec_nanos(); keep the Some(Timespec { ... }) to
ensure timeout_ptr is non-zero for finite timeouts (identifiers: Timespec,
timeout, timeout_ptr).

---

Nitpick comments:
In `@library/std/src/sys/thread/vibix.rs`:
- Around line 198-206: The current code performs an unsafe pointer cast from
AtomicU32 to crate::sync::atomic::Atomic<u32> when calling futex_wait, which is
fragile; change the API or call site to avoid this raw cast by either (A)
updating crate::sys::futex::futex_wait to accept &AtomicU32 directly, or (B)
introduce a clear type alias/newtype that maps crate::sync::atomic::Atomic<u32>
to AtomicU32 and use that alias at the call site, then pass &data.child_tid
without the unsafe pointer trick; update the futex_wait signature and all
callers (futex_wait) or add the alias/newtype and a safe conversion impl to
replace the unsafe cast around data.child_tid.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: a5696684-097e-488c-9f60-0711c2dafdd6

📥 Commits

Reviewing files that changed from the base of the PR and between a335c0b and 1e5dd8b.

📒 Files selected for processing (12)

• library/std/src/sys/pal/vibix/futex.rs
• library/std/src/sys/pal/vibix/mod.rs
• library/std/src/sys/sync/condvar/mod.rs
• library/std/src/sys/sync/mutex/mod.rs
• library/std/src/sys/sync/once/mod.rs
• library/std/src/sys/sync/rwlock/mod.rs
• library/std/src/sys/sync/thread_parking/mod.rs
• library/std/src/sys/thread/mod.rs
• library/std/src/sys/thread/vibix.rs
• userspace/vibix_abi/src/futex.rs
• userspace/vibix_abi/src/lib.rs
• userspace/vibix_abi/src/thread.rs