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[WIP] Add SemLock implementation to RustPython #6506

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34bbaf6
Initial plan
Copilot Dec 25, 2025
dcd74f1
Changes before error encountered
Copilot Dec 25, 2025
5a68008
Implement Unix SemLock and expose sem_unlink
Copilot Dec 25, 2025
4abfb6b
Fix missing sem_* symbols on libc targets
Copilot Dec 25, 2025
6c2a8fc
Fix SemLock constant interning to avoid panic
Copilot Dec 25, 2025
4af41d3
Fix cfg
youknowone Dec 25, 2025
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Implement Unix SemLock and expose sem_unlink 
Co-authored-by: youknowone <69878+youknowone@users.noreply.github.com>
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@youknowone
Copilot and youknowone committed Dec 25, 2025
commit 5a6800857bcb66cc5658e46a94a6fbeca7006095
129 changes: 69 additions & 60 deletions crates/stdlib/src/multiprocessing.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -45,9 +45,9 @@ mod _multiprocessing {
#[pymodule]
mod _multiprocessing {
use crate::vm::{
Context, FromArgs, Py, PyBaseExceptionRef, PyPayload, PyRef, PyResult, VirtualMachine,
builtins::PyTypeRef,
function::OptionalArg,
Context, FromArgs, Py, PyPayload, PyResult, VirtualMachine,
builtins::{PyBaseExceptionRef, PyType, PyTypeRef},
function::{FuncArgs, OptionalArg},
types::Constructor,
};
use libc::sem_t;
Expand All @@ -58,19 +58,21 @@ mod _multiprocessing {
time::Duration,
};

const RECURSIVE_MUTEX: i32 = 0;
const RECURSIVE_MUTEX_KIND: i32 = 0;
const SEMAPHORE_KIND: i32 = 1;
const SEM_VALUE_MAX_CONST: i32 = 32_767;

#[derive(FromArgs)]
struct SemLockArgs {
#[pyarg(positional_only)]
#[pyarg(positional)]
kind: i32,
#[pyarg(positional_only)]
#[pyarg(positional)]
value: i32,
#[pyarg(positional_only)]
#[pyarg(positional)]
maxvalue: i32,
#[pyarg(positional_only)]
#[pyarg(positional)]
name: String,
#[pyarg(positional_only)]
#[pyarg(positional)]
unlink: bool,
}

Expand Down Expand Up @@ -111,12 +113,7 @@ mod _multiprocessing {
) -> PyResult<(Self, Option<String>)> {
let cname = semaphore_name(vm, name)?;
let raw = unsafe {
libc::sem_open(
cname.as_ptr(),
libc::O_CREAT | libc::O_EXCL,
0o600,
value,
)
libc::sem_open(cname.as_ptr(), libc::O_CREAT | libc::O_EXCL, 0o600, value)
};
if raw == libc::SEM_FAILED {
let err = Errno::last();
Expand Down Expand Up @@ -158,37 +155,8 @@ mod _multiprocessing {
}
}

#[extend_class]
fn extend_class(ctx: &Context, class: &'static Py<crate::vm::builtins::PyType>) {
class.set_attr(
"SEM_VALUE_MAX",
ctx.new_int(libc::SEM_VALUE_MAX),
ctx,
);
}

#[pyclass(with(Constructor))]
impl SemLock {
#[pyslot]
fn slot_new(cls: PyTypeRef, args: SemLockArgs, vm: &VirtualMachine) -> PyResult {
if args.value < 0 || args.value > args.maxvalue {
return Err(vm.new_value_error("semaphore or lock value out of range".to_owned()));
}
let value = u32::try_from(args.value).map_err(|_| {
vm.new_value_error("semaphore or lock value out of range".to_owned())
})?;
let (handle, name) = SemHandle::create(&args.name, value, args.unlink, vm)?;
let zelf = SemLock {
handle,
kind: args.kind,
maxvalue: args.maxvalue,
name,
owner: AtomicU64::new(0),
count: AtomicUsize::new(0),
};
zelf.into_ref_with_type(vm, cls).map(Into::into)
}

#[pygetset]
fn handle(&self) -> isize {
self.handle.as_ptr() as isize
Expand Down Expand Up @@ -223,9 +191,7 @@ mod _multiprocessing {
}

let tid = current_thread_id();
if self.kind == RECURSIVE_MUTEX
&& self.owner.load(Ordering::Acquire) == tid
{
if self.kind == RECURSIVE_MUTEX_KIND && self.owner.load(Ordering::Acquire) == tid {
self.count.fetch_add(1, Ordering::Relaxed);
return Ok(true);
}
Expand Down Expand Up @@ -254,16 +220,17 @@ mod _multiprocessing {
#[pymethod]
fn release(&self, vm: &VirtualMachine) -> PyResult<()> {
let tid = current_thread_id();
if self.kind == RECURSIVE_MUTEX && self.owner.load(Ordering::Acquire) != tid {
if self.kind == RECURSIVE_MUTEX_KIND && self.owner.load(Ordering::Acquire) != tid {
return Err(vm.new_value_error("cannot release un-acquired lock".to_owned()));
}

if self.owner.load(Ordering::Acquire) == tid {
let owner_tid = self.owner.load(Ordering::Acquire);
if owner_tid == tid {
let current = self.count.load(Ordering::Acquire);
if current == 0 {
return Err(vm.new_value_error("cannot release un-acquired lock".to_owned()));
}
if self.kind == RECURSIVE_MUTEX && current > 1 {
if self.kind == RECURSIVE_MUTEX_KIND && current > 1 {
self.count.store(current - 1, Ordering::Release);
return Ok(());
}
Expand All @@ -272,6 +239,11 @@ mod _multiprocessing {
if new_val == 0 {
self.owner.store(0, Ordering::Release);
}
} else if self.kind != RECURSIVE_MUTEX_KIND {
// releasing semaphore or non-recursive lock from another thread;
// drop ownership information.
self.owner.store(0, Ordering::Release);
self.count.store(0, Ordering::Release);
}

let res = unsafe { libc::sem_post(self.handle.as_ptr()) };
Expand All @@ -282,8 +254,7 @@ mod _multiprocessing {
Ok(())
}

#[pymethod]
#[pyclass(name = "__enter__")]
#[pymethod(name = "__enter__")]
fn enter(&self, vm: &VirtualMachine) -> PyResult<bool> {
self.acquire(
AcquireArgs {
Expand All @@ -295,14 +266,15 @@ mod _multiprocessing {
}

#[pymethod]
fn __exit__(&self, _args: crate::vm::function::FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
fn __exit__(&self, _args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
self.release(vm)
}

#[pyclassmethod]
#[pymethod(name = "_rebuild")]
fn rebuild(
cls: PyTypeRef,
handle: isize,
_handle: isize,
kind: i32,
maxvalue: i32,
name: Option<String>,
Expand All @@ -320,8 +292,6 @@ mod _multiprocessing {
owner: AtomicU64::new(0),
count: AtomicUsize::new(0),
};
// handle is unused but kept for compatibility
let _ = handle;
zelf.into_ref_with_type(vm, cls).map(Into::into)
}

Expand Down Expand Up @@ -362,6 +332,24 @@ mod _multiprocessing {
}
}

#[extend_class]
fn extend_class(ctx: &Context, class: &Py<PyType>) {
class.set_attr(
ctx.interned_str("RECURSIVE_MUTEX")
.expect("intern RECURSIVE_MUTEX"),
ctx.new_int(RECURSIVE_MUTEX_KIND).into(),
);
class.set_attr(
ctx.interned_str("SEMAPHORE").expect("intern SEMAPHORE"),
ctx.new_int(SEMAPHORE_KIND).into(),
);
class.set_attr(
ctx.interned_str("SEM_VALUE_MAX")
.expect("intern SEM_VALUE_MAX"),
ctx.new_int(SEM_VALUE_MAX_CONST).into(),
);
}

fn wait(&self, vm: &VirtualMachine) -> PyResult<()> {
loop {
let res = unsafe { libc::sem_wait(self.handle.as_ptr()) };
Expand Down Expand Up @@ -390,8 +378,7 @@ mod _multiprocessing {

fn wait_timeout(&self, duration: Duration, vm: &VirtualMachine) -> PyResult<bool> {
let mut ts = current_timespec(vm)?;
let nsec_total =
ts.tv_nsec as i64 + i64::from(duration.subsec_nanos());
let nsec_total = ts.tv_nsec as i64 + i64::from(duration.subsec_nanos());
ts.tv_sec = ts
.tv_sec
.saturating_add(duration.as_secs() as libc::time_t + nsec_total / 1_000_000_000);
Expand All @@ -411,6 +398,28 @@ mod _multiprocessing {
}
}

impl Constructor for SemLock {
type Args = SemLockArgs;

fn py_new(_cls: &Py<PyType>, args: Self::Args, vm: &VirtualMachine) -> PyResult<Self> {
if args.value < 0 || args.value > args.maxvalue {
return Err(vm.new_value_error("semaphore or lock value out of range".to_owned()));
}
let value = u32::try_from(args.value).map_err(|_| {
vm.new_value_error("semaphore or lock value out of range".to_owned())
})?;
let (handle, name) = SemHandle::create(&args.name, value, args.unlink, vm)?;
Ok(SemLock {
handle,
kind: args.kind,
maxvalue: args.maxvalue,
name,
owner: AtomicU64::new(0),
count: AtomicUsize::new(0),
})
}
}

#[pyfunction]
fn sem_unlink(name: String, vm: &VirtualMachine) -> PyResult<()> {
let cname = semaphore_name(vm, &name)?;
Expand Down Expand Up @@ -461,11 +470,11 @@ mod _multiprocessing {
};
let text = msg.unwrap_or_else(|| err.desc().to_owned());
vm.new_os_subtype_error(exc_type, Some(err as i32), text)
.into()
.upcast()
}

fn current_thread_id() -> u64 {
std::thread::current().id().as_u64().get()
unsafe { libc::pthread_self() as u64 }
}
}

Expand Down