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src/concurrency/send-sync/examples.md

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+# Examples
+
+## `Send + Sync`
+
+Most types you come across are `Send + Sync`:
+
+* `i8`, `f32`, `bool`, `char`, `&str`, ...
+* `(T1, T2)`, `[T; N]`, `&[T]`, `struct { x: T }`, ...
+* `String`, `Option<T>`, `Vec<T>`, `Box<T>`, ...
+* `Arc<T>`: Explicitly thread-safe via atomic reference count.
+* `Mutex<T>`: Explicitly thread-safe via internal locking.
+* `AtomicBool`, `AtomicU8`, ...: Uses special atomic instructions.
+
+The generic types are typically `Send + Sync` when the type parameters are
+`Send + Sync`.
+
+## `Send + !Sync`
+
+These types can be moved to other threads, but they're not thread-safe.
+Typically because of interior mutability:
+
+* `mpsc::Sender<T>`
+* `mpsc::Receiver<T>`
+* `Cell<T>`
+* `RefCell<T>`
+
+## `!Send + Sync`
+
+These types are thread-safe, but they cannot be moved to another thread:
+
+* `MutexGuard<T>`: Uses OS level primitives which must be deallocated on the
+  thread which created them.
+
+## `!Send + !Sync`
+
+These types are not thread-safe and cannot be moved to other threads:
+
+* `Rc<T>`: each `Rc<T>` has a reference to an `RcBox<T>`, which contains a
+  non-atomic reference count.
+* `*const T`, `*mut T`: Rust that there are special lifetime considerations for the
+  pointer.