Sync

Synchronization primitives to build concurrent-safe and parallel-safe data structures in Crystal, so we can embrace MT with more serenity.

The provided sync primitives are meant to be useful yet low level. They can, and should, be used to protect simple resources, but also to build higher level constructs, for example an actor library.

The underlying implementation follows the nsync algorithm, that was easy to adapt from threads to fibers. Compared to a naive atomic+spinlock mutex, the algorithm is incredibly fast and efficient (much less wasted CPU time), and it eventually reaches a stable value, whatever how many fibers you put, while the naive implementation quickly goes exponential).

Status

Experimental: in progress work to flesh out sync primitives that we may want to have in Crystal's stdlib at some point.

Documentation

Run make docs or head to CrystalDoc.info.

Primitives

• Sync::Safe to annotate types as (a)sync safe.

• Sync::Lockable to abstract the different locks (internal).

• Sync::Mutex to protect critical sections using mutual exclusion.

• Sync::RWLock to protect critical sections using shared access and mutual exclusion.

• Sync::ConditionVariable to synchronize critical sections together.

• Sync::Exclusive(T) to protect a value T using mutual exclusion.

• Sync::Shared(T) to protect a value T using a mix of shared access and mutual exclusion.

• Sync::Future(T) to delegate the computation of a value T to another fiber.

• Sync::Map(K, V) for a distributed hash-like data structure.

TODO

• Sync::Semaphore (?)

Performance

While the performance of Mutex in stdlib is very performant when uncontended or with only a couple threads (MT:2), the nsync algorithm used by Sync::Mutex quickly proves much more performant and efficient, it even reaches expected performance and efficiency (whatever the number of fibers), while Mutex performance drops, and efficiency plummets (high CPU time).

Here are the results of running bench/mutex.cr in a multithreaded execution context (28 threads) on an Intel 14700K.

License

Distributed under the Apache-2.0 license. Use at your own risk.