778 lines
23 KiB
Rust
778 lines
23 KiB
Rust
use core::cell::UnsafeCell;
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use core::default::Default;
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use core::fmt;
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use core::marker::PhantomData;
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use core::mem;
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use core::ops::{Deref, DerefMut};
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use core::ptr::NonNull;
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use core::sync::atomic::{spin_loop_hint as cpu_relax, AtomicUsize, Ordering};
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/// A reader-writer lock
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///
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/// This type of lock allows a number of readers or at most one writer at any
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/// point in time. The write portion of this lock typically allows modification
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/// of the underlying data (exclusive access) and the read portion of this lock
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/// typically allows for read-only access (shared access).
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///
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/// The type parameter `T` represents the data that this lock protects. It is
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/// required that `T` satisfies `Send` to be shared across tasks and `Sync` to
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/// allow concurrent access through readers. The RAII guards returned from the
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/// locking methods implement `Deref` (and `DerefMut` for the `write` methods)
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/// to allow access to the contained of the lock.
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///
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/// An [`RwLockUpgradeableGuard`](RwLockUpgradeableGuard) can be upgraded to a
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/// writable guard through the [`RwLockUpgradeableGuard::upgrade`](RwLockUpgradeableGuard::upgrade)
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/// [`RwLockUpgradeableGuard::try_upgrade`](RwLockUpgradeableGuard::try_upgrade) functions.
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/// Writable or upgradeable guards can be downgraded through their respective `downgrade`
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/// functions.
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///
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/// Based on Facebook's
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/// [`folly/RWSpinLock.h`](https://github.com/facebook/folly/blob/a0394d84f2d5c3e50ebfd0566f9d3acb52cfab5a/folly/synchronization/RWSpinLock.h).
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/// This implementation is unfair to writers - if the lock always has readers, then no writers will
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/// ever get a chance. Using an upgradeable lock guard can *somewhat* alleviate this issue as no
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/// new readers are allowed when an upgradeable guard is held, but upgradeable guards can be taken
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/// when there are existing readers. However if the lock is that highly contended and writes are
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/// crucial then this implementation may be a poor choice.
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///
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/// # Examples
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///
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/// ```
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/// use spin;
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///
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/// let lock = spin::RwLock::new(5);
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///
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/// // many reader locks can be held at once
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/// {
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/// let r1 = lock.read();
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/// let r2 = lock.read();
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/// assert_eq!(*r1, 5);
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/// assert_eq!(*r2, 5);
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/// } // read locks are dropped at this point
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///
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/// // only one write lock may be held, however
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/// {
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/// let mut w = lock.write();
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/// *w += 1;
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/// assert_eq!(*w, 6);
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/// } // write lock is dropped here
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/// ```
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pub struct RwLock<T: ?Sized> {
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lock: AtomicUsize,
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data: UnsafeCell<T>,
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}
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const READER: usize = 1 << 2;
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const UPGRADED: usize = 1 << 1;
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const WRITER: usize = 1;
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/// A guard from which the protected data can be read
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///
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/// When the guard falls out of scope it will decrement the read count,
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/// potentially releasing the lock.
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#[derive(Debug)]
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pub struct RwLockReadGuard<'a, T: 'a + ?Sized> {
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lock: &'a AtomicUsize,
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data: NonNull<T>,
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}
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/// A guard to which the protected data can be written
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///
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/// When the guard falls out of scope it will release the lock.
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#[derive(Debug)]
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pub struct RwLockWriteGuard<'a, T: 'a + ?Sized> {
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lock: &'a AtomicUsize,
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data: NonNull<T>,
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#[doc(hidden)]
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_invariant: PhantomData<&'a mut T>,
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}
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/// A guard from which the protected data can be read, and can be upgraded
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/// to a writable guard if needed
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///
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/// No writers or other upgradeable guards can exist while this is in scope. New reader
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/// creation is prevented (to alleviate writer starvation) but there may be existing readers
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/// when the lock is acquired.
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///
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/// When the guard falls out of scope it will release the lock.
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#[derive(Debug)]
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pub struct RwLockUpgradeableGuard<'a, T: 'a + ?Sized> {
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lock: &'a AtomicUsize,
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data: NonNull<T>,
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#[doc(hidden)]
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_invariant: PhantomData<&'a mut T>,
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}
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// Same unsafe impls as `std::sync::RwLock`
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unsafe impl<T: ?Sized + Send> Send for RwLock<T> {}
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unsafe impl<T: ?Sized + Send + Sync> Sync for RwLock<T> {}
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impl<T> RwLock<T> {
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/// Creates a new spinlock wrapping the supplied data.
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///
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/// May be used statically:
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///
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/// ```
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/// use spin;
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///
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/// static RW_LOCK: spin::RwLock<()> = spin::RwLock::new(());
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///
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/// fn demo() {
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/// let lock = RW_LOCK.read();
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/// // do something with lock
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/// drop(lock);
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/// }
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/// ```
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#[inline]
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pub const fn new(user_data: T) -> RwLock<T> {
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RwLock {
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lock: AtomicUsize::new(0),
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data: UnsafeCell::new(user_data),
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}
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}
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/// Consumes this `RwLock`, returning the underlying data.
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#[inline]
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pub fn into_inner(self) -> T {
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// We know statically that there are no outstanding references to
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// `self` so there's no need to lock.
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let RwLock { data, .. } = self;
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data.into_inner()
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}
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}
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impl<T: ?Sized> RwLock<T> {
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/// Locks this rwlock with shared read access, blocking the current thread
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/// until it can be acquired.
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///
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/// The calling thread will be blocked until there are no more writers which
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/// hold the lock. There may be other readers currently inside the lock when
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/// this method returns. This method does not provide any guarantees with
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/// respect to the ordering of whether contentious readers or writers will
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/// acquire the lock first.
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///
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/// Returns an RAII guard which will release this thread's shared access
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/// once it is dropped.
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///
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/// ```
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/// let mylock = spin::RwLock::new(0);
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/// {
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/// let mut data = mylock.read();
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/// // The lock is now locked and the data can be read
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/// println!("{}", *data);
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/// // The lock is dropped
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/// }
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/// ```
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#[inline]
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pub fn read(&self) -> RwLockReadGuard<T> {
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loop {
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match self.try_read() {
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Some(guard) => return guard,
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None => cpu_relax(),
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}
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}
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}
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/// Attempt to acquire this lock with shared read access.
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///
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/// This function will never block and will return immediately if `read`
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/// would otherwise succeed. Returns `Some` of an RAII guard which will
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/// release the shared access of this thread when dropped, or `None` if the
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/// access could not be granted. This method does not provide any
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/// guarantees with respect to the ordering of whether contentious readers
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/// or writers will acquire the lock first.
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///
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/// ```
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/// let mylock = spin::RwLock::new(0);
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/// {
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/// match mylock.try_read() {
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/// Some(data) => {
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/// // The lock is now locked and the data can be read
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/// println!("{}", *data);
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/// // The lock is dropped
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/// },
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/// None => (), // no cigar
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/// };
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/// }
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/// ```
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#[inline]
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pub fn try_read(&self) -> Option<RwLockReadGuard<T>> {
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let value = self.lock.fetch_add(READER, Ordering::Acquire);
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// We check the UPGRADED bit here so that new readers are prevented when an UPGRADED lock is held.
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// This helps reduce writer starvation.
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if value & (WRITER | UPGRADED) != 0 {
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// Lock is taken, undo.
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self.lock.fetch_sub(READER, Ordering::Release);
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None
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} else {
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Some(RwLockReadGuard {
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lock: &self.lock,
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data: unsafe { NonNull::new_unchecked(self.data.get()) },
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})
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}
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}
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/// Force decrement the reader count.
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///
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/// This is *extremely* unsafe if there are outstanding `RwLockReadGuard`s
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/// live, or if called more times than `read` has been called, but can be
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/// useful in FFI contexts where the caller doesn't know how to deal with
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/// RAII. The underlying atomic operation uses `Ordering::Release`.
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#[inline]
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pub unsafe fn force_read_decrement(&self) {
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debug_assert!(self.lock.load(Ordering::Relaxed) & !WRITER > 0);
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self.lock.fetch_sub(READER, Ordering::Release);
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}
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/// Force unlock exclusive write access.
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///
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/// This is *extremely* unsafe if there are outstanding `RwLockWriteGuard`s
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/// live, or if called when there are current readers, but can be useful in
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/// FFI contexts where the caller doesn't know how to deal with RAII. The
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/// underlying atomic operation uses `Ordering::Release`.
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#[inline]
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pub unsafe fn force_write_unlock(&self) {
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debug_assert_eq!(self.lock.load(Ordering::Relaxed) & !(WRITER | UPGRADED), 0);
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self.lock.fetch_and(!(WRITER | UPGRADED), Ordering::Release);
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}
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#[inline(always)]
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fn try_write_internal(&self, strong: bool) -> Option<RwLockWriteGuard<T>> {
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if compare_exchange(
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&self.lock,
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0,
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WRITER,
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Ordering::Acquire,
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Ordering::Relaxed,
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strong,
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)
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.is_ok()
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{
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Some(RwLockWriteGuard {
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lock: &self.lock,
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data: unsafe { NonNull::new_unchecked(self.data.get()) },
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_invariant: PhantomData,
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})
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} else {
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None
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}
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}
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/// Lock this rwlock with exclusive write access, blocking the current
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/// thread until it can be acquired.
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///
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/// This function will not return while other writers or other readers
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/// currently have access to the lock.
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///
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/// Returns an RAII guard which will drop the write access of this rwlock
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/// when dropped.
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///
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/// ```
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/// let mylock = spin::RwLock::new(0);
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/// {
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/// let mut data = mylock.write();
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/// // The lock is now locked and the data can be written
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/// *data += 1;
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/// // The lock is dropped
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/// }
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/// ```
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#[inline]
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pub fn write(&self) -> RwLockWriteGuard<T> {
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loop {
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match self.try_write_internal(false) {
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Some(guard) => return guard,
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None => cpu_relax(),
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}
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}
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}
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/// Attempt to lock this rwlock with exclusive write access.
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///
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/// This function does not ever block, and it will return `None` if a call
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/// to `write` would otherwise block. If successful, an RAII guard is
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/// returned.
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///
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/// ```
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/// let mylock = spin::RwLock::new(0);
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/// {
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/// match mylock.try_write() {
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/// Some(mut data) => {
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/// // The lock is now locked and the data can be written
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/// *data += 1;
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/// // The lock is implicitly dropped
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/// },
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/// None => (), // no cigar
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/// };
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/// }
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/// ```
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#[inline]
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pub fn try_write(&self) -> Option<RwLockWriteGuard<T>> {
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self.try_write_internal(true)
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}
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/// Obtain a readable lock guard that can later be upgraded to a writable lock guard.
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/// Upgrades can be done through the [`RwLockUpgradeableGuard::upgrade`](RwLockUpgradeableGuard::upgrade) method.
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#[inline]
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pub fn upgradeable_read(&self) -> RwLockUpgradeableGuard<T> {
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loop {
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match self.try_upgradeable_read() {
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Some(guard) => return guard,
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None => cpu_relax(),
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}
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}
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}
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/// Tries to obtain an upgradeable lock guard.
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#[inline]
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pub fn try_upgradeable_read(&self) -> Option<RwLockUpgradeableGuard<T>> {
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if self.lock.fetch_or(UPGRADED, Ordering::Acquire) & (WRITER | UPGRADED) == 0 {
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Some(RwLockUpgradeableGuard {
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lock: &self.lock,
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data: unsafe { NonNull::new_unchecked(self.data.get()) },
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_invariant: PhantomData,
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})
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} else {
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// We can't unflip the UPGRADED bit back just yet as there is another upgradeable or write lock.
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// When they unlock, they will clear the bit.
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None
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}
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}
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}
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impl<T: ?Sized + fmt::Debug> fmt::Debug for RwLock<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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match self.try_read() {
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Some(guard) => write!(f, "RwLock {{ data: ")
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.and_then(|()| (&*guard).fmt(f))
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.and_then(|()| write!(f, "}}")),
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None => write!(f, "RwLock {{ <locked> }}"),
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}
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}
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}
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impl<T: ?Sized + Default> Default for RwLock<T> {
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fn default() -> RwLock<T> {
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RwLock::new(Default::default())
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}
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}
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impl<'rwlock, T: ?Sized> RwLockUpgradeableGuard<'rwlock, T> {
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#[inline(always)]
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fn try_upgrade_internal(self, strong: bool) -> Result<RwLockWriteGuard<'rwlock, T>, Self> {
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if compare_exchange(
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&self.lock,
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UPGRADED,
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WRITER,
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Ordering::Acquire,
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Ordering::Relaxed,
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strong,
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)
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.is_ok()
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{
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// Upgrade successful
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let out = Ok(RwLockWriteGuard {
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lock: &self.lock,
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data: self.data,
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_invariant: PhantomData,
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});
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// Forget the old guard so its destructor doesn't run
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mem::forget(self);
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out
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} else {
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Err(self)
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}
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}
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/// Upgrades an upgradeable lock guard to a writable lock guard.
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///
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/// ```
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/// let mylock = spin::RwLock::new(0);
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///
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/// let upgradeable = mylock.upgradeable_read(); // Readable, but not yet writable
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/// let writable = upgradeable.upgrade();
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/// ```
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#[inline]
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pub fn upgrade(mut self) -> RwLockWriteGuard<'rwlock, T> {
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loop {
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self = match self.try_upgrade_internal(false) {
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Ok(guard) => return guard,
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Err(e) => e,
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};
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cpu_relax();
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}
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}
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/// Tries to upgrade an upgradeable lock guard to a writable lock guard.
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///
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/// ```
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/// let mylock = spin::RwLock::new(0);
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/// let upgradeable = mylock.upgradeable_read(); // Readable, but not yet writable
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///
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/// match upgradeable.try_upgrade() {
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/// Ok(writable) => /* upgrade successful - use writable lock guard */ (),
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/// Err(upgradeable) => /* upgrade unsuccessful */ (),
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/// };
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/// ```
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#[inline]
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pub fn try_upgrade(self) -> Result<RwLockWriteGuard<'rwlock, T>, Self> {
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self.try_upgrade_internal(true)
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}
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#[inline]
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/// Downgrades the upgradeable lock guard to a readable, shared lock guard. Cannot fail and is guaranteed not to spin.
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///
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/// ```
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/// let mylock = spin::RwLock::new(1);
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///
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/// let upgradeable = mylock.upgradeable_read();
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/// assert!(mylock.try_read().is_none());
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/// assert_eq!(*upgradeable, 1);
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///
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/// let readable = upgradeable.downgrade(); // This is guaranteed not to spin
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/// assert!(mylock.try_read().is_some());
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/// assert_eq!(*readable, 1);
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/// ```
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pub fn downgrade(self) -> RwLockReadGuard<'rwlock, T> {
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// Reserve the read guard for ourselves
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self.lock.fetch_add(READER, Ordering::Acquire);
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RwLockReadGuard {
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lock: &self.lock,
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data: self.data,
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}
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// Dropping self removes the UPGRADED bit
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}
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}
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impl<'rwlock, T: ?Sized> RwLockWriteGuard<'rwlock, T> {
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/// Downgrades the writable lock guard to a readable, shared lock guard. Cannot fail and is guaranteed not to spin.
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///
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/// ```
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/// let mylock = spin::RwLock::new(0);
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///
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/// let mut writable = mylock.write();
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/// *writable = 1;
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///
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/// let readable = writable.downgrade(); // This is guaranteed not to spin
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/// # let readable_2 = mylock.try_read().unwrap();
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/// assert_eq!(*readable, 1);
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/// ```
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#[inline]
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pub fn downgrade(self) -> RwLockReadGuard<'rwlock, T> {
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// Reserve the read guard for ourselves
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self.lock.fetch_add(READER, Ordering::Acquire);
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RwLockReadGuard {
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lock: &self.lock,
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data: self.data,
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}
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// Dropping self removes the WRITER bit
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}
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}
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impl<'rwlock, T: ?Sized> Deref for RwLockReadGuard<'rwlock, T> {
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type Target = T;
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fn deref(&self) -> &T {
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unsafe { self.data.as_ref() }
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}
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}
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impl<'rwlock, T: ?Sized> Deref for RwLockUpgradeableGuard<'rwlock, T> {
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type Target = T;
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fn deref(&self) -> &T {
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unsafe { self.data.as_ref() }
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}
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}
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impl<'rwlock, T: ?Sized> Deref for RwLockWriteGuard<'rwlock, T> {
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type Target = T;
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fn deref(&self) -> &T {
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unsafe { self.data.as_ref() }
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}
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}
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impl<'rwlock, T: ?Sized> DerefMut for RwLockWriteGuard<'rwlock, T> {
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fn deref_mut(&mut self) -> &mut T {
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unsafe { self.data.as_mut() }
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}
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}
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impl<'rwlock, T: ?Sized> Drop for RwLockReadGuard<'rwlock, T> {
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fn drop(&mut self) {
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|
debug_assert!(self.lock.load(Ordering::Relaxed) & !(WRITER | UPGRADED) > 0);
|
|
self.lock.fetch_sub(READER, Ordering::Release);
|
|
}
|
|
}
|
|
|
|
impl<'rwlock, T: ?Sized> Drop for RwLockUpgradeableGuard<'rwlock, T> {
|
|
fn drop(&mut self) {
|
|
debug_assert_eq!(
|
|
self.lock.load(Ordering::Relaxed) & (WRITER | UPGRADED),
|
|
UPGRADED
|
|
);
|
|
self.lock.fetch_sub(UPGRADED, Ordering::AcqRel);
|
|
}
|
|
}
|
|
|
|
impl<'rwlock, T: ?Sized> Drop for RwLockWriteGuard<'rwlock, T> {
|
|
fn drop(&mut self) {
|
|
debug_assert_eq!(self.lock.load(Ordering::Relaxed) & WRITER, WRITER);
|
|
|
|
// Writer is responsible for clearing both WRITER and UPGRADED bits.
|
|
// The UPGRADED bit may be set if an upgradeable lock attempts an upgrade while this lock is held.
|
|
self.lock.fetch_and(!(WRITER | UPGRADED), Ordering::Release);
|
|
}
|
|
}
|
|
|
|
#[inline(always)]
|
|
fn compare_exchange(
|
|
atomic: &AtomicUsize,
|
|
current: usize,
|
|
new: usize,
|
|
success: Ordering,
|
|
failure: Ordering,
|
|
strong: bool,
|
|
) -> Result<usize, usize> {
|
|
if strong {
|
|
atomic.compare_exchange(current, new, success, failure)
|
|
} else {
|
|
atomic.compare_exchange_weak(current, new, success, failure)
|
|
}
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use std::prelude::v1::*;
|
|
|
|
use std::sync::atomic::{AtomicUsize, Ordering};
|
|
use std::sync::mpsc::channel;
|
|
use std::sync::Arc;
|
|
use std::thread;
|
|
|
|
use super::*;
|
|
|
|
#[derive(Eq, PartialEq, Debug)]
|
|
struct NonCopy(i32);
|
|
|
|
#[test]
|
|
fn smoke() {
|
|
let l = RwLock::new(());
|
|
drop(l.read());
|
|
drop(l.write());
|
|
drop((l.read(), l.read()));
|
|
drop(l.write());
|
|
}
|
|
|
|
// TODO: needs RNG
|
|
//#[test]
|
|
//fn frob() {
|
|
// static R: RwLock = RwLock::new();
|
|
// const N: usize = 10;
|
|
// const M: usize = 1000;
|
|
//
|
|
// let (tx, rx) = channel::<()>();
|
|
// for _ in 0..N {
|
|
// let tx = tx.clone();
|
|
// thread::spawn(move|| {
|
|
// let mut rng = rand::thread_rng();
|
|
// for _ in 0..M {
|
|
// if rng.gen_weighted_bool(N) {
|
|
// drop(R.write());
|
|
// } else {
|
|
// drop(R.read());
|
|
// }
|
|
// }
|
|
// drop(tx);
|
|
// });
|
|
// }
|
|
// drop(tx);
|
|
// let _ = rx.recv();
|
|
// unsafe { R.destroy(); }
|
|
//}
|
|
|
|
#[test]
|
|
fn test_rw_arc() {
|
|
let arc = Arc::new(RwLock::new(0));
|
|
let arc2 = arc.clone();
|
|
let (tx, rx) = channel();
|
|
|
|
thread::spawn(move || {
|
|
let mut lock = arc2.write();
|
|
for _ in 0..10 {
|
|
let tmp = *lock;
|
|
*lock = -1;
|
|
thread::yield_now();
|
|
*lock = tmp + 1;
|
|
}
|
|
tx.send(()).unwrap();
|
|
});
|
|
|
|
// Readers try to catch the writer in the act
|
|
let mut children = Vec::new();
|
|
for _ in 0..5 {
|
|
let arc3 = arc.clone();
|
|
children.push(thread::spawn(move || {
|
|
let lock = arc3.read();
|
|
assert!(*lock >= 0);
|
|
}));
|
|
}
|
|
|
|
// Wait for children to pass their asserts
|
|
for r in children {
|
|
assert!(r.join().is_ok());
|
|
}
|
|
|
|
// Wait for writer to finish
|
|
rx.recv().unwrap();
|
|
let lock = arc.read();
|
|
assert_eq!(*lock, 10);
|
|
}
|
|
|
|
#[test]
|
|
fn test_rw_access_in_unwind() {
|
|
let arc = Arc::new(RwLock::new(1));
|
|
let arc2 = arc.clone();
|
|
let _ = thread::spawn(move || -> () {
|
|
struct Unwinder {
|
|
i: Arc<RwLock<isize>>,
|
|
}
|
|
impl Drop for Unwinder {
|
|
fn drop(&mut self) {
|
|
let mut lock = self.i.write();
|
|
*lock += 1;
|
|
}
|
|
}
|
|
let _u = Unwinder { i: arc2 };
|
|
panic!();
|
|
})
|
|
.join();
|
|
let lock = arc.read();
|
|
assert_eq!(*lock, 2);
|
|
}
|
|
|
|
#[test]
|
|
fn test_rwlock_unsized() {
|
|
let rw: &RwLock<[i32]> = &RwLock::new([1, 2, 3]);
|
|
{
|
|
let b = &mut *rw.write();
|
|
b[0] = 4;
|
|
b[2] = 5;
|
|
}
|
|
let comp: &[i32] = &[4, 2, 5];
|
|
assert_eq!(&*rw.read(), comp);
|
|
}
|
|
|
|
#[test]
|
|
fn test_rwlock_try_write() {
|
|
use std::mem::drop;
|
|
|
|
let lock = RwLock::new(0isize);
|
|
let read_guard = lock.read();
|
|
|
|
let write_result = lock.try_write();
|
|
match write_result {
|
|
None => (),
|
|
Some(_) => assert!(
|
|
false,
|
|
"try_write should not succeed while read_guard is in scope"
|
|
),
|
|
}
|
|
|
|
drop(read_guard);
|
|
}
|
|
|
|
#[test]
|
|
fn test_rw_try_read() {
|
|
let m = RwLock::new(0);
|
|
mem::forget(m.write());
|
|
assert!(m.try_read().is_none());
|
|
}
|
|
|
|
#[test]
|
|
fn test_into_inner() {
|
|
let m = RwLock::new(NonCopy(10));
|
|
assert_eq!(m.into_inner(), NonCopy(10));
|
|
}
|
|
|
|
#[test]
|
|
fn test_into_inner_drop() {
|
|
struct Foo(Arc<AtomicUsize>);
|
|
impl Drop for Foo {
|
|
fn drop(&mut self) {
|
|
self.0.fetch_add(1, Ordering::SeqCst);
|
|
}
|
|
}
|
|
let num_drops = Arc::new(AtomicUsize::new(0));
|
|
let m = RwLock::new(Foo(num_drops.clone()));
|
|
assert_eq!(num_drops.load(Ordering::SeqCst), 0);
|
|
{
|
|
let _inner = m.into_inner();
|
|
assert_eq!(num_drops.load(Ordering::SeqCst), 0);
|
|
}
|
|
assert_eq!(num_drops.load(Ordering::SeqCst), 1);
|
|
}
|
|
|
|
#[test]
|
|
fn test_force_read_decrement() {
|
|
let m = RwLock::new(());
|
|
::std::mem::forget(m.read());
|
|
::std::mem::forget(m.read());
|
|
::std::mem::forget(m.read());
|
|
assert!(m.try_write().is_none());
|
|
unsafe {
|
|
m.force_read_decrement();
|
|
m.force_read_decrement();
|
|
}
|
|
assert!(m.try_write().is_none());
|
|
unsafe {
|
|
m.force_read_decrement();
|
|
}
|
|
assert!(m.try_write().is_some());
|
|
}
|
|
|
|
#[test]
|
|
fn test_force_write_unlock() {
|
|
let m = RwLock::new(());
|
|
::std::mem::forget(m.write());
|
|
assert!(m.try_read().is_none());
|
|
unsafe {
|
|
m.force_write_unlock();
|
|
}
|
|
assert!(m.try_read().is_some());
|
|
}
|
|
|
|
#[test]
|
|
fn test_upgrade_downgrade() {
|
|
let m = RwLock::new(());
|
|
{
|
|
let _r = m.read();
|
|
let upg = m.try_upgradeable_read().unwrap();
|
|
assert!(m.try_read().is_none());
|
|
assert!(m.try_write().is_none());
|
|
assert!(upg.try_upgrade().is_err());
|
|
}
|
|
{
|
|
let w = m.write();
|
|
assert!(m.try_upgradeable_read().is_none());
|
|
let _r = w.downgrade();
|
|
assert!(m.try_upgradeable_read().is_some());
|
|
assert!(m.try_read().is_some());
|
|
assert!(m.try_write().is_none());
|
|
}
|
|
{
|
|
let _u = m.upgradeable_read();
|
|
assert!(m.try_upgradeable_read().is_none());
|
|
}
|
|
|
|
assert!(m.try_upgradeable_read().unwrap().try_upgrade().is_ok());
|
|
}
|
|
}
|