Crate lockable

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The lockable library offers thread-safe HashMap (see LockableHashMap), LruCache (see LockableLruCache) and LockPool (see LockPool) types. In all of these dat atypes, individual keys can be locked/unlocked, even if there is no entry for this key in the map or cache.

This can be very useful for synchronizing access to an underlying key-value store or for building cache data structures on top of such a key-value store.

§LRU cache example

This example builds a simple LRU cache and locks some entries.

use lockable::{AsyncLimit, LockableLruCache};

let lockable_cache = LockableLruCache::<i64, String>::new();

// Insert an entry
lockable_cache.async_lock(4, AsyncLimit::no_limit())
    .await?
    .insert(String::from("Value"));

// Hold a lock on a different entry
let guard = lockable_cache.async_lock(5, AsyncLimit::no_limit())
    .await?;

// This next line would wait until the lock gets released,
// which in this case would cause a deadlock because we're
// on the same thread
// let guard2 = lockable_cache.async_lock(5, AsyncLimit::no_limit())
//    .await?;

// After dropping the corresponding guard, we can lock it again
std::mem::drop(guard);
let guard2 = lockable_cache.async_lock(5, AsyncLimit::no_limit())
    .await?;

§Lockpool example

This example builds a simple lock pool using the LockPool data structure. A lock pool is a pool of keyable locks. This can be used if you don’t need a cache but just some way to synchronize access to an underlying resource.

use lockable::LockPool;

let lockpool = LockPool::new();
let guard1 = lockpool.async_lock(4).await;
let guard2 = lockpool.async_lock(5).await;

// This next line would wait until the lock gets released,
// which in this case would cause a deadlock because we're
// on the same thread.
// let guard3 = lockpool.async_lock(4).await;

// After dropping the corresponding guard, we can lock it again
std::mem::drop(guard1);
let guard3 = lockpool.async_lock(4).await;

§HashMap example

If you need a lockable key-value store but don’t need the LRU ordering, you can use LockableHashMap.

use lockable::{AsyncLimit, LockableHashMap};

let lockable_map = LockableHashMap::<i64, String>::new();

// Insert an entry
lockable_map.async_lock(4, AsyncLimit::no_limit())
    .await?
    .insert(String::from("Value"));

// Hold a lock on a different entry
let guard = lockable_map.async_lock(5, AsyncLimit::no_limit())
    .await?;

// This next line would wait until the lock gets released,
// which in this case would cause a deadlock because we're
// on the same thread
// let guard2 = lockable_map.async_lock(5, AsyncLimit::no_limit())
//    .await?;

// After dropping the corresponding guard, we can lock it again
std::mem::drop(guard);
let guard2 = lockable_map.async_lock(5, AsyncLimit::no_limit())
    .await?;

§Crate Features

Structs§

  • Guard
    A RAII implementation of a scoped lock for locks from a LockableHashMap or LockableLruCache. When this instance is dropped (falls out of scope), the lock will be unlocked.
  • LockPool
    A pool of locks where individual locks can be locked/unlocked by key. It initially considers all keys as “unlocked”, but they can be locked and if a second thread tries to acquire a lock for the same key, they will have to wait.
  • LockableHashMap
    A threadsafe hash map where individual keys can be locked/unlocked, even if there is no entry for this key in the map. It initially considers all keys as “unlocked”, but they can be locked and if a second thread tries to acquire a lock for the same key, they will have to wait.
  • LockableLruCache
    A threadsafe LRU cache where individual keys can be locked/unlocked, even if there is no entry for this key in the cache. It initially considers all keys as “unlocked”, but they can be locked and if a second thread tries to acquire a lock for the same key, they will have to wait.

Enums§

  • AsyncLimit
    An instance of this enum defines a limit on the number of entries in a LockableLruCache or a LockableHashMap. It can be used to cause old entries to be evicted if a limit on the number of entries is exceeded in a call to the following functions:
  • Never
    A type that can never be instantiated. This can be used in a Result<T, Never> to indicate that an operation cannot return an error.
  • SyncLimit
    An instance of this enum defines a limit on the number of entries in a LockableLruCache or a LockableHashMap. It can be used to cause old entries to be evicted if a limit on the number of entries is exceeded in a call to the following functions:
  • TryInsertError
    This error is thrown by Guard::try_insert if the entry already exists

Traits§