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Add rustc_diagnostic_item to sys::Mutex methods #141690

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Merged
merged 3 commits into from
May 29, 2025
Merged

Add rustc_diagnostic_item to sys::Mutex methods #141690

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2e99a88
Add diagnostic items to sys::Mutex
Patrick-6 May 28, 2025
149b5b2
Make pthread Mutex internals less public
Patrick-6 May 28, 2025
8237107
Add comments to diagnostic items
Patrick-6 May 28, 2025
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3 changes: 3 additions & 0 deletions compiler/rustc_span/src/symbol.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2071,6 +2071,9 @@ symbols! {
sym,
sync,
synthetic,
sys_mutex_lock,
sys_mutex_try_lock,
sys_mutex_unlock,
t32,
target,
target_abi,
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6 changes: 6 additions & 0 deletions library/std/src/sys/sync/mutex/futex.rs
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Expand Up @@ -19,11 +19,15 @@ impl Mutex {
}

#[inline]
// Make this a diagnostic item for Miri's concurrency model checker.
#[cfg_attr(not(test), rustc_diagnostic_item = "sys_mutex_try_lock")]
pub fn try_lock(&self) -> bool {
self.futex.compare_exchange(UNLOCKED, LOCKED, Acquire, Relaxed).is_ok()
}

#[inline]
// Make this a diagnostic item for Miri's concurrency model checker.
#[cfg_attr(not(test), rustc_diagnostic_item = "sys_mutex_lock")]
pub fn lock(&self) {
if self.futex.compare_exchange(UNLOCKED, LOCKED, Acquire, Relaxed).is_err() {
self.lock_contended();
Expand Down Expand Up @@ -80,6 +84,8 @@ impl Mutex {
}

#[inline]
// Make this a diagnostic item for Miri's concurrency model checker.
#[cfg_attr(not(test), rustc_diagnostic_item = "sys_mutex_unlock")]
pub unsafe fn unlock(&self) {
if self.futex.swap(UNLOCKED, Release) == CONTENDED {
// We only wake up one thread. When that thread locks the mutex, it
Expand Down
8 changes: 7 additions & 1 deletion library/std/src/sys/sync/mutex/pthread.rs
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Expand Up @@ -6,7 +6,7 @@ use crate::sys::pal::sync as pal;
use crate::sys::sync::OnceBox;

pub struct Mutex {
pub pal: OnceBox<pal::Mutex>,
pub(in crate::sys::sync) pal: OnceBox<pal::Mutex>,
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Is this needed for Miri or just a pedantic change? Makes sense in either case.

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Just a pedantic change.

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To give more context -- the model checking for mutexes would become weird or even unsound if the mutex API is bypassed by directly accessing the underlying mutex operations, so we wanted to reduce the risk of that happening.

}

impl Mutex {
Expand All @@ -28,20 +28,26 @@ impl Mutex {
}

#[inline]
// Make this a diagnostic item for Miri's concurrency model checker.
#[cfg_attr(not(test), rustc_diagnostic_item = "sys_mutex_lock")]
pub fn lock(&self) {
// SAFETY: we call `init` above, therefore reentrant locking is safe.
// In `drop` we ensure that the mutex is not destroyed while locked.
unsafe { self.get().lock() }
}

#[inline]
// Make this a diagnostic item for Miri's concurrency model checker.
#[cfg_attr(not(test), rustc_diagnostic_item = "sys_mutex_unlock")]
pub unsafe fn unlock(&self) {
// SAFETY: the mutex can only be locked if it is already initialized
// and we observed this initialization since we observed the locking.
unsafe { self.pal.get_unchecked().unlock() }
}

#[inline]
// Make this a diagnostic item for Miri's concurrency model checker.
#[cfg_attr(not(test), rustc_diagnostic_item = "sys_mutex_try_lock")]
pub fn try_lock(&self) -> bool {
// SAFETY: we call `init` above, therefore reentrant locking is safe.
// In `drop` we ensure that the mutex is not destroyed while locked.
Expand Down
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