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diff --git a/third_party/rust/signal-hook-registry/src/half_lock.rs b/third_party/rust/signal-hook-registry/src/half_lock.rs
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+//! The half-lock structure
+//!
+//! We need a way to protect the structure with configured hooks ‒ a signal may happen in arbitrary
+//! thread and needs to read them while another thread might be manipulating the structure.
+//!
+//! Under ordinary circumstances we would be happy to just use `Mutex<HashMap<c_int, _>>`. However,
+//! as we use it in the signal handler, we are severely limited in what we can or can't use. So we
+//! choose to implement kind of spin-look thing with atomics.
+//!
+//! In the reader it is always simply locked and then unlocked, making sure it doesn't disappear
+//! while in use.
+//!
+//! The writer has a separate mutex (that prevents other writers; this is used outside of the
+//! signal handler), makes a copy of the data and swaps an atomic pointer to the data structure.
+//! But it waits until everything is unlocked (no signal handler has the old data) for dropping the
+//! old instance. There's a generation trick to make sure that new signal locks another instance.
+//!
+//! The downside is, this is an active spin lock at the writer end. However, we assume than:
+//!
+//! * Signals are one time setup before we actually have threads. We just need to make *sure* we
+//!   are safe even if this is not true.
+//! * Signals are rare, happening at the same time as the write even rarer.
+//! * Signals are short, as there is mostly nothing allowed inside them anyway.
+//! * Our tool box is severely limited.
+//!
+//! Therefore this is hopefully reasonable trade-off.
+//!
+//! # Atomic orderings
+//!
+//! The whole code uses SeqCst conservatively. Atomics are not used because of performance here and
+//! are the minor price around signals anyway. But the comments state which orderings should be
+//! enough in practice in case someone wants to get inspired (but do make your own check through
+//! them anyway).
+
+use std::isize;
+use std::marker::PhantomData;
+use std::ops::Deref;
+use std::sync::atomic::{self, AtomicPtr, AtomicUsize, Ordering};
+use std::sync::{Mutex, MutexGuard, PoisonError};
+use std::thread;
+
+use libc;
+
+const YIELD_EVERY: usize = 16;
+const MAX_GUARDS: usize = (isize::MAX) as usize;
+
+pub(crate) struct ReadGuard<'a, T: 'a> {
+    data: &'a T,
+    lock: &'a AtomicUsize,
+}
+
+impl<'a, T> Deref for ReadGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.data
+    }
+}
+
+impl<'a, T> Drop for ReadGuard<'a, T> {
+    fn drop(&mut self) {
+        // We effectively unlock; Release would be enough.
+        self.lock.fetch_sub(1, Ordering::SeqCst);
+    }
+}
+
+pub(crate) struct WriteGuard<'a, T: 'a> {
+    _guard: MutexGuard<'a, ()>,
+    lock: &'a HalfLock<T>,
+    data: &'a T,
+}
+
+impl<'a, T> WriteGuard<'a, T> {
+    pub(crate) fn store(&mut self, val: T) {
+        // Move to the heap and convert to raw pointer for AtomicPtr.
+        let new = Box::into_raw(Box::new(val));
+
+        self.data = unsafe { &*new };
+
+        // We can just put the new value in here safely, we worry only about dropping the old one.
+        // Release might (?) be enough, to "upload" the data.
+        let old = self.lock.data.swap(new, Ordering::SeqCst);
+
+        // Now we make sure there's no reader having the old data.
+        self.lock.write_barrier();
+
+        drop(unsafe { Box::from_raw(old) });
+    }
+}
+
+impl<'a, T> Deref for WriteGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        // Protected by that mutex
+        self.data
+    }
+}
+
+pub(crate) struct HalfLock<T> {
+    // We conceptually contain an instance of T
+    _t: PhantomData<T>,
+    // The actual data as a pointer.
+    data: AtomicPtr<T>,
+    // The generation of the data. Influences which slot of the lock counter we use.
+    generation: AtomicUsize,
+    // How many active locks are there?
+    lock: [AtomicUsize; 2],
+    // Mutex for the writers; only one writer.
+    write_mutex: Mutex<()>,
+}
+
+impl<T> HalfLock<T> {
+    pub(crate) fn new(data: T) -> Self {
+        // Move to the heap so we can safely point there. Then convert to raw pointer as AtomicPtr
+        // operates on raw pointers. The AtomicPtr effectively acts like Box for us semantically.
+        let ptr = Box::into_raw(Box::new(data));
+        Self {
+            _t: PhantomData,
+            data: AtomicPtr::new(ptr),
+            generation: AtomicUsize::new(0),
+            lock: [AtomicUsize::new(0), AtomicUsize::new(0)],
+            write_mutex: Mutex::new(()),
+        }
+    }
+
+    pub(crate) fn read(&self) -> ReadGuard<T> {
+        // Relaxed should be enough; we only pick one or the other slot and the writer observes
+        // that both were 0 at some time. So the actual value doesn't really matter for safety,
+        // only the changing improves the performance.
+        let gen = self.generation.load(Ordering::SeqCst);
+        let lock = &self.lock[gen % 2];
+        // Effectively locking something, acquire should be enough.
+        let guard_cnt = lock.fetch_add(1, Ordering::SeqCst);
+
+        // This is to prevent overflowing the counter in some degenerate cases, which could lead to
+        // UB (freeing data while still in use). However, as this data structure is used only
+        // internally and it's not possible to leak the guard and the guard itself takes some
+        // memory, it should be really impossible to trigger this case. Still, we include it from
+        // abundance of caution.
+        //
+        // This technically is not fully correct as enough threads being in between here and the
+        // abort below could still overflow it and it could get freed for some *other* thread, but
+        // that would mean having too many active threads to fit into RAM too and is even more
+        // absurd corner case than the above.
+        if guard_cnt > MAX_GUARDS {
+            unsafe { libc::abort() };
+        }
+
+        // Acquire should be enough; we need to "download" the data, paired with the swap on the
+        // same pointer.
+        let data = self.data.load(Ordering::SeqCst);
+        // Safe:
+        // * It did point to valid data when put in.
+        // * Protected by lock, so still valid.
+        let data = unsafe { &*data };
+
+        ReadGuard { data, lock }
+    }
+
+    fn update_seen(&self, seen_zero: &mut [bool; 2]) {
+        for (seen, slot) in seen_zero.iter_mut().zip(&self.lock) {
+            *seen = *seen || slot.load(Ordering::SeqCst) == 0;
+        }
+    }
+
+    fn write_barrier(&self) {
+        // Do a first check of seeing zeroes before we switch the generation. At least one of them
+        // should be zero by now, due to having drained the generation before leaving the previous
+        // writer.
+        let mut seen_zero = [false; 2];
+        self.update_seen(&mut seen_zero);
+        // By switching the generation to the other slot, we make sure the currently active starts
+        // draining while the other will start filling up.
+        self.generation.fetch_add(1, Ordering::SeqCst); // Overflow is fine.
+
+        let mut iter = 0usize;
+        while !seen_zero.iter().all(|s| *s) {
+            iter = iter.wrapping_add(1);
+
+            // Be somewhat less aggressive while looping, switch to the other threads if possible.
+            if cfg!(not(miri)) {
+                if iter % YIELD_EVERY == 0 {
+                    thread::yield_now();
+                } else {
+                    // Replaced by hint::spin_loop, but we want to support older compiler
+                    #[allow(deprecated)]
+                    atomic::spin_loop_hint();
+                }
+            }
+
+            self.update_seen(&mut seen_zero);
+        }
+    }
+
+    pub(crate) fn write(&self) -> WriteGuard<T> {
+        // While it's possible the user code panics, our code in store doesn't and the data gets
+        // swapped atomically. So if it panics, nothing gets changed, therefore poisons are of no
+        // interest here.
+        let guard = self
+            .write_mutex
+            .lock()
+            .unwrap_or_else(PoisonError::into_inner);
+
+        // Relaxed should be enough, as we are under the same mutex that was used to get the data
+        // in.
+        let data = self.data.load(Ordering::SeqCst);
+        // Safe:
+        // * Stored as valid data
+        // * Only this method, protected by mutex, can change the pointer, so it didn't go away.
+        let data = unsafe { &*data };
+
+        WriteGuard {
+            data,
+            _guard: guard,
+            lock: self,
+        }
+    }
+}
+
+impl<T> Drop for HalfLock<T> {
+    fn drop(&mut self) {
+        // During drop we are sure there are no other borrows of the data so we are free to just
+        // drop it. Also, the drop impl won't be called in practice in our case, as it is used
+        // solely as a global variable, but we provide it for completeness and tests anyway.
+        //
+        // unsafe: the pointer in there is always valid, we just take the last instance out.
+        unsafe {
+            // Acquire should be enough.
+            let data = Box::from_raw(self.data.load(Ordering::SeqCst));
+            drop(data);
+        }
+    }
+}