Struct serenity::prelude::RwLock [−][src]
pub struct RwLock<T> where
T: ?Sized, { /* fields omitted */ }
Expand description
An asynchronous reader-writer lock
This type of lock allows a number of readers or at most one writer at any point in time. The write portion of this lock typically allows modification of the underlying data (exclusive access) and the read portion of this lock typically allows for read-only access (shared access).
In comparison, a Mutex
does not distinguish between readers or writers
that acquire the lock, therefore causing any tasks waiting for the lock to
become available to yield. An RwLock
will allow any number of readers to
acquire the lock as long as a writer is not holding the lock.
The priority policy of Tokio’s read-write lock is fair (or
write-preferring), in order to ensure that readers cannot starve
writers. Fairness is ensured using a first-in, first-out queue for the tasks
awaiting the lock; if a task that wishes to acquire the write lock is at the
head of the queue, read locks will not be given out until the write lock has
been released. This is in contrast to the Rust standard library’s
std::sync::RwLock
, where the priority policy is dependent on the
operating system’s implementation.
The type parameter T
represents the data that this lock protects. It is
required that T
satisfies Send
to be shared across threads. The RAII guards
returned from the locking methods implement Deref
(and DerefMut
for the write
methods) to allow access to the content of the lock.
Examples
use tokio::sync::RwLock;
#[tokio::main]
async fn main() {
let lock = RwLock::new(5);
// many reader locks can be held at once
{
let r1 = lock.read().await;
let r2 = lock.read().await;
assert_eq!(*r1, 5);
assert_eq!(*r2, 5);
} // read locks are dropped at this point
// only one write lock may be held, however
{
let mut w = lock.write().await;
*w += 1;
assert_eq!(*w, 6);
} // write lock is dropped here
}
Implementations
Creates a new instance of an RwLock<T>
which is unlocked.
Examples
use tokio::sync::RwLock;
let lock = RwLock::new(5);
Locks this rwlock with shared read access, causing the current task to yield until the lock has been acquired.
The calling task will yield until there are no more writers which hold the lock. There may be other readers currently inside the lock when this method returns.
Examples
use std::sync::Arc;
use tokio::sync::RwLock;
#[tokio::main]
async fn main() {
let lock = Arc::new(RwLock::new(1));
let c_lock = lock.clone();
let n = lock.read().await;
assert_eq!(*n, 1);
tokio::spawn(async move {
// While main has an active read lock, we acquire one too.
let r = c_lock.read().await;
assert_eq!(*r, 1);
}).await.expect("The spawned task has paniced");
// Drop the guard after the spawned task finishes.
drop(n);
}
Locks this rwlock with exclusive write access, causing the current task to yield until the lock has been acquired.
This function will not return while other writers or other readers currently have access to the lock.
Returns an RAII guard which will drop the write access of this rwlock when dropped.
Examples
use tokio::sync::RwLock;
#[tokio::main]
async fn main() {
let lock = RwLock::new(1);
let mut n = lock.write().await;
*n = 2;
}
Consumes the lock, returning the underlying data.
Trait Implementations
Auto Trait Implementations
impl<T> !RefUnwindSafe for RwLock<T>
impl<T: ?Sized> UnwindSafe for RwLock<T> where
T: UnwindSafe,
Blanket Implementations
Mutably borrows from an owned value. Read more
Instruments this type with the provided Span
, returning an
Instrumented
wrapper. Read more
Instruments this type with the provided Span
, returning an
Instrumented
wrapper. Read more
Attaches the provided Subscriber
to this type, returning a
WithDispatch
wrapper. Read more
Attaches the current default Subscriber
to this type, returning a
WithDispatch
wrapper. Read more