Crate sharded_mutex

ShardedMutex, atomic Everything

This library provides global locks for (pseudo-) atomic access to data without memory overhead per object. Concurrency is improved by selecting a Mutex from a pool based on the Address of the object to be locked.

Even being sharded, these Mutexes act still as global and non-recursive locks. One must not lock another object while a lock on the same type/domain is already hold, otherwise deadlocks will happen.

There is one pool of mutexes per guarded type, thus it is possible to lock values of different types at the same time. Further a ‘multi_lock’ API allows to obtain locks on multiple objects of the same type at the same time.

This pool of mutexes per types comes with a cost. In the current implementation each pool needs 256 bytes. Thus using ShardedMutex makes only sense for types when significantly more than 256 instances are to be expected.

Same types may have different locking domains using type tags.

Provides pseudo atomic access for types that implement Copy and PartialEq.

In debug builds a deadlock detector is active which will panic when one tries to lock objects from the same type/domain while already holding a lock.

Example usage:

use sharded_mutex::ShardedMutex;

// create 2 values that need locking
let x = ShardedMutex::new(123);
let y = ShardedMutex::new(234);

// a single lock
assert_eq!(*x.lock(), 123);

// Multiple locks
let mut guards = ShardedMutex::multi_lock([&x, &y]);

assert_eq!(*guards[0], 123);
assert_eq!(*guards[1], 234);

// can write as well
*guards[1] = 456;

// unlocks
drop(guards);

// lock again
assert_eq!(*y.lock(), 456);

// Pseudo atomic access
use sharded_mutex::PseudoAtomicOps;

x.store(&234);
assert_eq!(x.load(), 234);

let mut swapping = 345;
x.swap(&mut swapping);
assert_eq!(swapping, 234);
assert_eq!(x.load(), 345);

assert!(!x.compare_and_set(&123, &456));
assert!(x.compare_and_set(&345, &456));
assert_eq!(x.load(), 456);

Macros

sharded_mutex

Every type that is used within a ShardedMutex needs to implement some boilerplate (assoc_static). For common non-generic standard types this is already done. For your own types you need to implement this by placing sharded_mutex!(YourType) into your source. When some std type is missing, please send me a note or a PR’s. Types from external crates which can’t be implemented by ‘sharded_mutex’ or by yourself need to be wraped in a newtype. The ‘TAG’ is required when you want to implement a sharded mutex over foreign types that are not implemented in your crate. This can be any (non-generic) type your crate defines, preferably you just make a zero-size struct just for this purpose.

Structs

ShardedMutex

Wraps a ‘T’ that can only be accessed through global mutexes at zero memory overhead per object. The optional ‘TAG’ is used to create locking domains which share locks.

ShardedMutexGuard

The guard returned from locking a ShardedMutex. Dropping this will unlock the mutex. Access to the underlying value is done by dereferencing this guard.

Traits

PseudoAtomicOps

Include this trait to get atomics like access for types that implement Copy and PartialEq