# Struct std::sync::RwLock [−] [src]

    pub struct RwLock<T: ?Sized> {
        // some fields omitted
    }

A 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).

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.

The type parameter `T` represents the data that this lock protects. It is required that `T` satisfies `Send` to be shared across threads and `Sync` to allow concurrent access through readers. The RAII guards returned from the locking methods implement `Deref` (and `DerefMut` for the `write` methods) to allow access to the contained of the lock.

# Poisoning

RwLocks, like Mutexes, will become poisoned on panics. Note, however, that an RwLock may only be poisoned if a panic occurs while it is locked exclusively (write mode). If a panic occurs in any reader, then the lock will not be poisoned.

# Examples

fn main() { use std::sync::RwLock; let lock = RwLock::new(5); // many reader 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 // only one write lock may be held, however { let mut w = lock.write().unwrap(); *w += 1; assert_eq!(*w, 6); } // write lock is dropped here }

    use std::sync::RwLock;

    let lock = RwLock::new(5);

    // many reader 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

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

## Methods

### `impl<T> RwLock<T>`

#### `fn new(t: T) -> RwLock<T>`

Creates a new instance of an `RwLock<T>` which is unlocked.

# Examples

fn main() { use std::sync::RwLock; let lock = RwLock::new(5); }

    use std::sync::RwLock;

    let lock = RwLock::new(5);

### `impl<T: ?Sized> RwLock<T>`

#### `fn read(&self) -> LockResult<RwLockReadGuard<T>>`

Locks this rwlock 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 an RAII guard which will release this thread's shared access once it is dropped.

# Failure

This function will return an error if the RwLock is poisoned. An RwLock is poisoned whenever a writer panics while holding an exclusive lock. The failure will occur immediately after the lock has been acquired.

#### `fn try_read(&self) -> TryLockResult<RwLockReadGuard<T>>`

Attempts to acquire this rwlock with shared read access.

If the access could not be granted at this time, then `Err` is returned. Otherwise, an RAII guard is returned which will release the shared access when it is dropped.

This function does not block.

This function does not provide any guarantees with respect to the ordering of whether contentious readers or writers will acquire the lock first.

# Failure

This function will return an error if the RwLock is poisoned. An RwLock is poisoned whenever a writer panics while holding an exclusive lock. An error will only be returned if the lock would have otherwise been acquired.

#### `fn write(&self) -> LockResult<RwLockWriteGuard<T>>`

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

# Failure

This function will return an error if the RwLock is poisoned. An RwLock is poisoned whenever a writer panics while holding an exclusive lock. An error will be returned when the lock is acquired.

#### `fn try_write(&self) -> TryLockResult<RwLockWriteGuard<T>>`

Attempts to lock this rwlock with exclusive write access.

If the lock could not be acquired at this time, then `Err` is returned. Otherwise, an RAII guard is returned which will release the lock when it is dropped.

This function does not block.

This function does not provide any guarantees with respect to the ordering of whether contentious readers or writers will acquire the lock first.

# Failure

This function will return an error if the RwLock is poisoned. An RwLock is poisoned whenever a writer panics while holding an exclusive lock. An error will only be returned if the lock would have otherwise been acquired.

#### `fn is_poisoned(&self) -> bool`

Determines whether the lock is poisoned.

If another thread is active, the lock can still become poisoned at any time. You should not trust a `false` value for program correctness without additional synchronization.

#### `fn into_inner(self) -> LockResult<T> where T: Sized`

Consumes this `RwLock`, returning the underlying data.

# Failure

This function will return an error if the RwLock is poisoned. An RwLock is poisoned whenever a writer panics while holding an exclusive lock. An error will only be returned if the lock would have otherwise been acquired.

#### `fn get_mut(&mut self) -> LockResult<&mut T>`

Returns a mutable reference to the underlying data.

Since this call borrows the `RwLock` mutably, no actual locking needs to take place---the mutable borrow statically guarantees no locks exist.

# Failure

This function will return an error if the RwLock is poisoned. An RwLock is poisoned whenever a writer panics while holding an exclusive lock. An error will only be returned if the lock would have otherwise been acquired.

## Trait Implementations

### `impl<T: ?Sized> RecoverSafe for RwLock<T>`

### `impl<T: ?Sized + Send + Sync> Send for RwLock<T>`

### `impl<T: ?Sized + Send + Sync> Sync for RwLock<T>`

### `impl<T: ?Sized> Drop for RwLock<T>`

#### `fn drop(&mut self)`

### `impl<T: ?Sized + Debug> Debug for RwLock<T>`

#### `fn fmt(&self, f: &mut Formatter) -> Result`

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