Struct crossbeam::sync::ShardedLock

source ·
pub struct ShardedLock<T>
where T: ?Sized,
{ /* private fields */ }
Expand description

A sharded reader-writer lock.

This lock is equivalent to RwLock, except read operations are faster and write operations are slower.

A ShardedLock is internally made of a list of shards, each being a RwLock occupying a single cache line. Read operations will pick one of the shards depending on the current thread and lock it. Write operations need to lock all shards in succession.

By splitting the lock into shards, concurrent read operations will in most cases choose different shards and thus update different cache lines, which is good for scalability. However, write operations need to do more work and are therefore slower than usual.

The priority policy of the lock is dependent on the underlying operating system’s implementation, and this type does not guarantee that any particular policy will be used.

§Poisoning

A ShardedLock, like RwLock, will become poisoned on a panic. Note that it may only be poisoned if a panic occurs while a write operation is in progress. If a panic occurs in any read operation, the lock will not be poisoned.

§Examples

use crossbeam_utils::sync::ShardedLock;

let lock = ShardedLock::new(5);

// Any number of read locks can be held at once.
{
    let r1 = lock.read().unwrap();
    let r2 = lock.read().unwrap();
    assert_eq!(*r1, 5);
    assert_eq!(*r2, 5);
} // Read locks are dropped at this point.

// However, only one write lock may be held.
{
    let mut w = lock.write().unwrap();
    *w += 1;
    assert_eq!(*w, 6);
} // Write lock is dropped here.

Implementations§

source§

impl<T> ShardedLock<T>

source

pub fn new(value: T) -> ShardedLock<T>

Creates a new sharded reader-writer lock.

§Examples
use crossbeam_utils::sync::ShardedLock;

let lock = ShardedLock::new(5);
source

pub fn into_inner(self) -> Result<T, PoisonError<T>>

Consumes this lock, returning the underlying data.

§Errors

This method will return an error if the lock is poisoned. A lock gets poisoned when a write operation panics.

§Examples
use crossbeam_utils::sync::ShardedLock;

let lock = ShardedLock::new(String::new());
{
    let mut s = lock.write().unwrap();
    *s = "modified".to_owned();
}
assert_eq!(lock.into_inner().unwrap(), "modified");
source§

impl<T> ShardedLock<T>
where T: ?Sized,

source

pub fn is_poisoned(&self) -> bool

Returns true if the lock is poisoned.

If another thread can still access the lock, it may become poisoned at any time. A false result should not be trusted without additional synchronization.

§Examples
use crossbeam_utils::sync::ShardedLock;
use std::sync::Arc;
use std::thread;

let lock = Arc::new(ShardedLock::new(0));
let c_lock = lock.clone();

let _ = thread::spawn(move || {
    let _lock = c_lock.write().unwrap();
    panic!(); // the lock gets poisoned
}).join();
assert_eq!(lock.is_poisoned(), true);
source

pub fn get_mut(&mut self) -> Result<&mut T, PoisonError<&mut T>>

Returns a mutable reference to the underlying data.

Since this call borrows the lock mutably, no actual locking needs to take place.

§Errors

This method will return an error if the lock is poisoned. A lock gets poisoned when a write operation panics.

§Examples
use crossbeam_utils::sync::ShardedLock;

let mut lock = ShardedLock::new(0);
*lock.get_mut().unwrap() = 10;
assert_eq!(*lock.read().unwrap(), 10);
source

pub fn try_read( &self ) -> Result<ShardedLockReadGuard<'_, T>, TryLockError<ShardedLockReadGuard<'_, T>>>

Attempts to acquire this lock with shared read access.

If the access could not be granted at this time, an error is returned. Otherwise, a guard is returned which will release the shared access when it is dropped. This method does not provide any guarantees with respect to the ordering of whether contentious readers or writers will acquire the lock first.

§Errors

This method will return an error if the lock is poisoned. A lock gets poisoned when a write operation panics.

§Examples
use crossbeam_utils::sync::ShardedLock;

let lock = ShardedLock::new(1);

match lock.try_read() {
    Ok(n) => assert_eq!(*n, 1),
    Err(_) => unreachable!(),
};
source

pub fn read( &self ) -> Result<ShardedLockReadGuard<'_, T>, PoisonError<ShardedLockReadGuard<'_, T>>>

Locks with shared read access, blocking the current thread until it can be acquired.

The calling thread will be blocked until there are no more writers which hold the lock. There may be other readers currently inside the lock when this method returns. This method does not provide any guarantees with respect to the ordering of whether contentious readers or writers will acquire the lock first.

Returns a guard which will release the shared access when dropped.

§Errors

This method will return an error if the lock is poisoned. A lock gets poisoned when a write operation panics.

§Panics

This method might panic when called if the lock is already held by the current thread.

§Examples
use crossbeam_utils::sync::ShardedLock;
use std::sync::Arc;
use std::thread;

let lock = Arc::new(ShardedLock::new(1));
let c_lock = lock.clone();

let n = lock.read().unwrap();
assert_eq!(*n, 1);

thread::spawn(move || {
    let r = c_lock.read();
    assert!(r.is_ok());
}).join().unwrap();
source

pub fn try_write( &self ) -> Result<ShardedLockWriteGuard<'_, T>, TryLockError<ShardedLockWriteGuard<'_, T>>>

Attempts to acquire this lock with exclusive write access.

If the access could not be granted at this time, an error is returned. Otherwise, a guard is returned which will release the exclusive access when it is dropped. This method does not provide any guarantees with respect to the ordering of whether contentious readers or writers will acquire the lock first.

§Errors

This method will return an error if the lock is poisoned. A lock gets poisoned when a write operation panics.

§Examples
use crossbeam_utils::sync::ShardedLock;

let lock = ShardedLock::new(1);

let n = lock.read().unwrap();
assert_eq!(*n, 1);

assert!(lock.try_write().is_err());
source

pub fn write( &self ) -> Result<ShardedLockWriteGuard<'_, T>, PoisonError<ShardedLockWriteGuard<'_, T>>>

Locks with exclusive write access, blocking the current thread until it can be acquired.

The calling thread will be blocked until there are no more writers which hold the lock. There may be other readers currently inside the lock when this method returns. This method does not provide any guarantees with respect to the ordering of whether contentious readers or writers will acquire the lock first.

Returns a guard which will release the exclusive access when dropped.

§Errors

This method will return an error if the lock is poisoned. A lock gets poisoned when a write operation panics.

§Panics

This method might panic when called if the lock is already held by the current thread.

§Examples
use crossbeam_utils::sync::ShardedLock;

let lock = ShardedLock::new(1);

let mut n = lock.write().unwrap();
*n = 2;

assert!(lock.try_read().is_err());

Trait Implementations§

source§

impl<T> Debug for ShardedLock<T>
where T: Debug + ?Sized,

source§

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
source§

impl<T> Default for ShardedLock<T>
where T: Default,

source§

fn default() -> ShardedLock<T>

Returns the “default value” for a type. Read more
source§

impl<T> From<T> for ShardedLock<T>

source§

fn from(t: T) -> ShardedLock<T>

Converts to this type from the input type.
source§

impl<T> RefUnwindSafe for ShardedLock<T>
where T: ?Sized,

source§

impl<T> Send for ShardedLock<T>
where T: Send + ?Sized,

source§

impl<T> Sync for ShardedLock<T>
where T: Send + Sync + ?Sized,

source§

impl<T> UnwindSafe for ShardedLock<T>
where T: ?Sized,

Auto Trait Implementations§

§

impl<T: ?Sized> Unpin for ShardedLock<T>
where T: Unpin,

Blanket Implementations§

source§

impl<T> Any for T
where T: 'static + ?Sized,

source§

fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
source§

impl<T> Borrow<T> for T
where T: ?Sized,

source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

impl<T> BorrowMut<T> for T
where T: ?Sized,

source§

fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
source§

impl<T> From<!> for T

source§

fn from(t: !) -> T

Converts to this type from the input type.
source§

impl<T> From<T> for T

source§

fn from(t: T) -> T

Returns the argument unchanged.

source§

impl<T, U> Into<U> for T
where U: From<T>,

source§

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

source§

impl<T> Pointable for T

source§

const ALIGN: usize = _

The alignment of pointer.
§

type Init = T

The type for initializers.
source§

unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
source§

unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
source§

unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
source§

unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
source§

impl<T, U> TryFrom<U> for T
where U: Into<T>,

§

type Error = Infallible

The type returned in the event of a conversion error.
source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

§

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.