Struct RwLock

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pub struct RwLock<T> { /* private fields */ }

Expand description

Smart pointer to tokio::sync::RwLock.

Wraps acquiring the lock into timeout with a Duration of 30 seconds by default.

Implementations§

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impl<T> RwLock<T>

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pub fn new(value: T) -> Self

Create new RwLock with default timeout of 30 seconds.

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pub fn new_with_timeout(value: T, timeout: Duration) -> Self

Create new RwLock with given timeout.

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pub async fn read(&self) -> RwLockReadGuard<'_, T>

Wrapper around tokio::sync::RwLock::read(). Will time out if the lock can’t get acquired until the timeout is reached.

§Panics

Panics when timeout is reached.

Source

pub async fn read_err(&self) -> Result<RwLockReadGuard<'_, T>>

Wrapper around tokio::sync::RwLock::read(). Will time out if the lock can’t get acquired until the timeout is reached.

Returns an error if timeout is reached.

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pub async fn write(&self) -> RwLockWriteGuard<'_, T>

Wrapper around tokio::sync::RwLock::write(). Will time out if the lock can’t get acquired until the timeout is reached.

§Panics

Panics when timeout is reached.

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pub async fn write_err(&self) -> Result<RwLockWriteGuard<'_, T>>

Wrapper around tokio::sync::RwLock::write(). Will time out if the lock can’t get acquired until the timeout is reached.

Returns an error if timeout is reached.

Methods from Deref<Target = RwLock<T>>§

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pub async fn read(&self) -> RwLockReadGuard<'_, T>

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 writers which hold the lock. There may be other readers inside the lock when the task resumes.

Note that under the priority policy of RwLock, read locks are not granted until prior write locks, to prevent starvation. Therefore deadlock may occur if a read lock is held by the current task, a write lock attempt is made, and then a subsequent read lock attempt is made by the current task.

Returns an RAII guard which will drop this read access of the RwLock when dropped.

§Cancel safety

This method uses a queue to fairly distribute locks in the order they were requested. Cancelling a call to read makes you lose your place in the queue.

§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 panicked");

    // Drop the guard after the spawned task finishes.
    drop(n);
}

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pub fn blocking_read(&self) -> RwLockReadGuard<'_, T>

Blockingly locks this RwLock with shared read access.

This method is intended for use cases where you need to use this rwlock in asynchronous code as well as in synchronous code.

Returns an RAII guard which will drop the read access of this RwLock when dropped.

§Panics

This function panics if called within an asynchronous execution context.

If you find yourself in an asynchronous execution context and needing to call some (synchronous) function which performs one of these blocking_ operations, then consider wrapping that call inside [spawn_blocking()][crate::runtime::Handle::spawn_blocking] (or [block_in_place()][crate::task::block_in_place]).

§Examples

use std::sync::Arc;
use tokio::sync::RwLock;

#[tokio::main]
async fn main() {
    let rwlock = Arc::new(RwLock::new(1));
    let mut write_lock = rwlock.write().await;

    let blocking_task = tokio::task::spawn_blocking({
        let rwlock = Arc::clone(&rwlock);
        move || {
            // This shall block until the `write_lock` is released.
            let read_lock = rwlock.blocking_read();
            assert_eq!(*read_lock, 0);
        }
    });

    *write_lock -= 1;
    drop(write_lock); // release the lock.

    // Await the completion of the blocking task.
    blocking_task.await.unwrap();

    // Assert uncontended.
    assert!(rwlock.try_write().is_ok());
}

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pub async fn read_owned(self: Arc<RwLock<T>>) -> OwnedRwLockReadGuard<T>

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 writers which hold the lock. There may be other readers inside the lock when the task resumes.

This method is identical to RwLock::read, except that the returned guard references the RwLock with an Arc rather than by borrowing it. Therefore, the RwLock must be wrapped in an Arc to call this method, and the guard will live for the 'static lifetime, as it keeps the RwLock alive by holding an Arc.

Note that under the priority policy of RwLock, read locks are not granted until prior write locks, to prevent starvation. Therefore deadlock may occur if a read lock is held by the current task, a write lock attempt is made, and then a subsequent read lock attempt is made by the current task.

Returns an RAII guard which will drop this read access of the RwLock when dropped.

§Cancel safety

This method uses a queue to fairly distribute locks in the order they were requested. Cancelling a call to read_owned makes you lose your place in the queue.

§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_owned().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_owned().await;
        assert_eq!(*r, 1);
    }).await.expect("The spawned task has panicked");

    // Drop the guard after the spawned task finishes.
    drop(n);
}

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

Attempts to acquire this RwLock with shared read access.

If the access couldn’t be acquired immediately, returns TryLockError. Otherwise, an RAII guard is returned which will release read access when dropped.

§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 v = lock.try_read().unwrap();
    assert_eq!(*v, 1);

    tokio::spawn(async move {
        // While main has an active read lock, we acquire one too.
        let n = c_lock.read().await;
        assert_eq!(*n, 1);
    }).await.expect("The spawned task has panicked");

    // Drop the guard when spawned task finishes.
    drop(v);
}

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pub fn try_read_owned( self: Arc<RwLock<T>>, ) -> Result<OwnedRwLockReadGuard<T>, TryLockError>

Attempts to acquire this RwLock with shared read access.

If the access couldn’t be acquired immediately, returns TryLockError. Otherwise, an RAII guard is returned which will release read access when dropped.

This method is identical to RwLock::try_read, except that the returned guard references the RwLock with an Arc rather than by borrowing it. Therefore, the RwLock must be wrapped in an Arc to call this method, and the guard will live for the 'static lifetime, as it keeps the RwLock alive by holding an Arc.

§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 v = lock.try_read_owned().unwrap();
    assert_eq!(*v, 1);

    tokio::spawn(async move {
        // While main has an active read lock, we acquire one too.
        let n = c_lock.read_owned().await;
        assert_eq!(*n, 1);
    }).await.expect("The spawned task has panicked");

    // Drop the guard when spawned task finishes.
    drop(v);
}

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pub async fn write(&self) -> RwLockWriteGuard<'_, T>

Locks this RwLock with exclusive write access, causing the current task to yield until the lock has been acquired.

The calling task will yield while other writers or readers currently have access to the lock.

Returns an RAII guard which will drop the write access of this RwLock when dropped.

§Cancel safety

This method uses a queue to fairly distribute locks in the order they were requested. Cancelling a call to write makes you lose your place in the queue.

§Examples

use tokio::sync::RwLock;

#[tokio::main]
async fn main() {
  let lock = RwLock::new(1);

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

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pub fn blocking_write(&self) -> RwLockWriteGuard<'_, T>

Blockingly locks this RwLock with exclusive write access.

This method is intended for use cases where you need to use this rwlock in asynchronous code as well as in synchronous code.

Returns an RAII guard which will drop the write access of this RwLock when dropped.

§Panics

This function panics if called within an asynchronous execution context.

If you find yourself in an asynchronous execution context and needing to call some (synchronous) function which performs one of these blocking_ operations, then consider wrapping that call inside [spawn_blocking()][crate::runtime::Handle::spawn_blocking] (or [block_in_place()][crate::task::block_in_place]).

§Examples

use std::sync::Arc;
use tokio::{sync::RwLock};

#[tokio::main]
async fn main() {
    let rwlock =  Arc::new(RwLock::new(1));
    let read_lock = rwlock.read().await;

    let blocking_task = tokio::task::spawn_blocking({
        let rwlock = Arc::clone(&rwlock);
        move || {
            // This shall block until the `read_lock` is released.
            let mut write_lock = rwlock.blocking_write();
            *write_lock = 2;
        }
    });

    assert_eq!(*read_lock, 1);
    // Release the last outstanding read lock.
    drop(read_lock);

    // Await the completion of the blocking task.
    blocking_task.await.unwrap();

    // Assert uncontended.
    let read_lock = rwlock.try_read().unwrap();
    assert_eq!(*read_lock, 2);
}

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pub async fn write_owned(self: Arc<RwLock<T>>) -> OwnedRwLockWriteGuard<T>

Locks this RwLock with exclusive write access, causing the current task to yield until the lock has been acquired.

The calling task will yield while other writers or readers currently have access to the lock.

This method is identical to RwLock::write, except that the returned guard references the RwLock with an Arc rather than by borrowing it. Therefore, the RwLock must be wrapped in an Arc to call this method, and the guard will live for the 'static lifetime, as it keeps the RwLock alive by holding an Arc.

Returns an RAII guard which will drop the write access of this RwLock when dropped.

§Cancel safety

This method uses a queue to fairly distribute locks in the order they were requested. Cancelling a call to write_owned makes you lose your place in the queue.

§Examples

use std::sync::Arc;
use tokio::sync::RwLock;

#[tokio::main]
async fn main() {
  let lock = Arc::new(RwLock::new(1));

  let mut n = lock.write_owned().await;
  *n = 2;
}

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

Attempts to acquire this RwLock with exclusive write access.

If the access couldn’t be acquired immediately, returns TryLockError. Otherwise, an RAII guard is returned which will release write access when dropped.

§Examples

use tokio::sync::RwLock;

#[tokio::main]
async fn main() {
    let rw = RwLock::new(1);

    let v = rw.read().await;
    assert_eq!(*v, 1);

    assert!(rw.try_write().is_err());
}

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pub fn try_write_owned( self: Arc<RwLock<T>>, ) -> Result<OwnedRwLockWriteGuard<T>, TryLockError>

Attempts to acquire this RwLock with exclusive write access.

If the access couldn’t be acquired immediately, returns TryLockError. Otherwise, an RAII guard is returned which will release write access when dropped.

This method is identical to RwLock::try_write, except that the returned guard references the RwLock with an Arc rather than by borrowing it. Therefore, the RwLock must be wrapped in an Arc to call this method, and the guard will live for the 'static lifetime, as it keeps the RwLock alive by holding an Arc.

§Examples

use std::sync::Arc;
use tokio::sync::RwLock;

#[tokio::main]
async fn main() {
    let rw = Arc::new(RwLock::new(1));

    let v = Arc::clone(&rw).read_owned().await;
    assert_eq!(*v, 1);

    assert!(rw.try_write_owned().is_err());
}