Function core::ptr::read_volatile

pub unsafe fn read_volatile<T>(src: *const T) -> T

Performs a volatile read of the value from src without moving it. This leaves the memory in src unchanged.

Volatile operations are intended to act on I/O memory, and are guaranteed to not be elided or reordered by the compiler across other volatile operations.

Memory read with read_volatile should almost always be written to using write_volatile.

Notes

Rust does not currently have a rigorously and formally defined memory model, so the precise semantics of what "volatile" means here is subject to change over time. That being said, the semantics will almost always end up pretty similar to C11's definition of volatile.

The compiler shouldn't change the relative order or number of volatile memory operations. However, volatile memory operations on zero-sized types (e.g. if a zero-sized type is passed to read_volatile) are no-ops and may be ignored.

Safety

Behavior is undefined if any of the following conditions are violated:

• src must be valid.

• src must be properly aligned.

Like read, read_unaligned creates a bitwise copy of T, regardless of whether T is Copy. If T is not Copy, using both the returned value and the value at *src can [violate memory safety][read-ownership]. However, storing non-Copy types in volatile memory is almost certainly incorrect.

Examples

Basic usage:

let x = 12;
let y = &x as *const i32;

unsafe {
    assert_eq!(std::ptr::read_volatile(y), 12);
}