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Add documentation on migrating away from compare_and_swap

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This commit is contained in:
Linus Färnstrand 2020-11-20 22:16:15 +01:00
parent 3abba5e21f
commit 4252e48256
1 changed files with 51 additions and 0 deletions
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51
library/core/src/sync/atomic.rs
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@ -464,6 +464,23 @@ pub fn swap(&self, val: bool, order: Ordering) -> bool {
/// **Note:** This method is only available on platforms that support atomic
/// operations on `u8`.
///
/// # Migrating to `compare_exchange` and `compare_exchange_weak`
///
/// `compare_and_swap` is equivalent to `compare_exchange` with the following mapping for
/// memory orderings:
///
/// Original | Success | Failure
/// -------- | ------- | -------
/// Relaxed | Relaxed | Relaxed
/// Acquire | Acquire | Acquire
/// Release | Release | Relaxed
/// AcqRel | AcqRel | Acquire
/// SeqCst | SeqCst | SeqCst
///
/// `compare_exchange_weak` is allowed to fail spuriously even when the comparison succeeds,
/// which allows the compiler to generate better assembly code when the compare and swap
/// is used in a loop.
///
/// # Examples
///
/// ```
@ -1070,6 +1087,23 @@ pub fn swap(&self, ptr: *mut T, order: Ordering) -> *mut T {
/// **Note:** This method is only available on platforms that support atomic
/// operations on pointers.
///
/// # Migrating to `compare_exchange` and `compare_exchange_weak`
///
/// `compare_and_swap` is equivalent to `compare_exchange` with the following mapping for
/// memory orderings:
///
/// Original | Success | Failure
/// -------- | ------- | -------
/// Relaxed | Relaxed | Relaxed
/// Acquire | Acquire | Acquire
/// Release | Release | Relaxed
/// AcqRel | AcqRel | Acquire
/// SeqCst | SeqCst | SeqCst
///
/// `compare_exchange_weak` is allowed to fail spuriously even when the comparison succeeds,
/// which allows the compiler to generate better assembly code when the compare and swap
/// is used in a loop.
///
/// # Examples
///
/// ```
@ -1612,6 +1646,23 @@ pub fn swap(&self, val: $int_type, order: Ordering) -> $int_type {
**Note**: This method is only available on platforms that support atomic
operations on [`", $s_int_type, "`](", $int_ref, ").
# Migrating to `compare_exchange` and `compare_exchange_weak`
`compare_and_swap` is equivalent to `compare_exchange` with the following mapping for
memory orderings:
Original | Success | Failure
-------- | ------- | -------
Relaxed | Relaxed | Relaxed
Acquire | Acquire | Acquire
Release | Release | Relaxed
AcqRel | AcqRel | Acquire
SeqCst | SeqCst | SeqCst
`compare_exchange_weak` is allowed to fail spuriously even when the comparison succeeds,
which allows the compiler to generate better assembly code when the compare and swap
is used in a loop.
# Examples
```