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52249e35
编写于
5月 19, 2018
作者:
J
Jake Goulding
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差异文件
UnsafeCell doc typos and minor flow improvements
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src/libcore/cell.rs
src/libcore/cell.rs
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src/libcore/cell.rs
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52249e35
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@@ -1231,25 +1231,26 @@ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
///
/// If you have a reference `&SomeStruct`, then normally in Rust all fields of `SomeStruct` are
/// immutable. The compiler makes optimizations based on the knowledge that `&T` is not mutably
/// aliased or mutated, and that `&mut T` is unique. `UnsafeCel<T>` is the only core language
/// aliased or mutated, and that `&mut T` is unique. `UnsafeCel
l
<T>` is the only core language
/// feature to work around this restriction. All other types that allow internal mutability, such as
/// `Cell<T>` and `RefCell<T>` use `UnsafeCell` to wrap their internal data.
/// `Cell<T>` and `RefCell<T>`
,
use `UnsafeCell` to wrap their internal data.
///
/// The `UnsafeCell` API itself is technically very simple: it gives you a raw pointer `*mut T` to
/// its contents. It is up to _you_ as the abstraction designer to use that raw pointer correctly.
///
/// The precise Rust aliasing rules are somewhat in flux, but the main points are not contentious:
///
/// - If you create a safe reference with lifetime `'a` (either a `&T` or `&mut T` reference) that
/// is accessible by safe code (for example, because you returned it), then you must not access
/// the data in any way that contradicts that reference for the remainder of `'a`. For example, that
/// means that if you take the `*mut T` from an `UnsafeCell<T>` and case it to an `&T`, then until
/// that reference's lifetime expires, the data in `T` must remain immutable (modulo any
/// `UnsafeCell` data found within `T`, of course). Similarly, if you create an `&mut T` reference
/// that is released to safe code, then you must not access the data within the `UnsafeCell` until
/// that reference expires.
/// - If you create a safe reference with lifetime `'a` (either a `&T` or `&mut T`
/// reference) that is accessible by safe code (for example, because you returned it),
/// then you must not access the data in any way that contradicts that reference for the
/// remainder of `'a`. For example, this means that if you take the `*mut T` from an
/// `UnsafeCell<T>` and cast it to an `&T`, then the data in `T` must remain immutable
/// (modulo any `UnsafeCell` data found within `T`, of course) until that reference's
/// lifetime expires. Similarly, if you create a `&mut T` reference that is released to
/// safe code, then you must not access the data within the `UnsafeCell` until that
/// reference expires.
///
/// - At all times, you must avoid data races
, meaning that i
f multiple threads have access to
/// - At all times, you must avoid data races
. I
f multiple threads have access to
/// the same `UnsafeCell`, then any writes must have a proper happens-before relation to all other
/// accesses (or use atomics).
///
...
...
@@ -1259,10 +1260,10 @@ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
/// 1. A `&T` reference can be released to safe code and there it can co-exit with other `&T`
/// references, but not with a `&mut T`
///
/// 2. A `&mut T` reference may be released to safe code
,
provided neither other `&mut T` nor `&T`
/// 2. A `&mut T` reference may be released to safe code provided neither other `&mut T` nor `&T`
/// co-exist with it. A `&mut T` must always be unique.
///
/// Note that while mutating or mutably aliasing the contents of an `&
UnsafeCell<T>` is
/// Note that while mutating or mutably aliasing the contents of an `&UnsafeCell<T>` is
/// okay (provided you enforce the invariants some other way), it is still undefined behavior
/// to have multiple `&mut UnsafeCell<T>` aliases.
///
...
...
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