README_sync_send.md

Extensible Concurrency with Sync and Send Traits

Interestingly Rust language has very few concurrency features. Almost every concurrency feature we have discussed so far is part of the standard library, not the language. The language talks about concurrency using two traits from std::marker. They are Sync and Send traits.

Allow transference of ownership between threads using Send trait

The Send trait marks that the ownership of values implementing the Send trait can be transferred between threads. Almost every Rust type implements Send trait. All primitive types implement the Send trait except for raw pointers. A composite type with all its members implementing Send trait is also considered to implement Send trait.

Allowing access from multiple threads with Sync

The Sync trait marks that the type implementing the Sync trait is safe to be shared between multiple threads. In other words for any type T is Sync if &T (immutable reference) implements Send. A composite type with all its members implementing Sync the composite type is also considered to implement Sync.

• Rc<T> is not Sync
• RefCell<T> is not Sync - the runtime borrow checking rules implemented in RefCell are not thread safe
• Mutex<T> is Sync

Implementing Sync and Send Manually is Unsafe

Any type that contains all Sync or Send traits is also considered Sync or Send safe. It is considered Unsafe to implement Sync or Send manually.