diff options
| -rw-r--r-- | src/doc/unstable-book/src/SUMMARY.md | 2 | ||||
| -rw-r--r-- | src/doc/unstable-book/src/compiler-fences.md (renamed from src/doc/unstable-book/src/compiler-barriers.md) | 20 | ||||
| -rw-r--r-- | src/libcore/sync/atomic.rs | 12 |
3 files changed, 17 insertions, 17 deletions
diff --git a/src/doc/unstable-book/src/SUMMARY.md b/src/doc/unstable-book/src/SUMMARY.md index 54e602a81db..b0cb444beaf 100644 --- a/src/doc/unstable-book/src/SUMMARY.md +++ b/src/doc/unstable-book/src/SUMMARY.md @@ -38,7 +38,7 @@ - [collections](collections.md) - [collections_range](collections-range.md) - [command_envs](command-envs.md) -- [compiler_barriers](compiler-barriers.md) +- [compiler_fences](compiler-fences.md) - [compiler_builtins](compiler-builtins.md) - [compiler_builtins_lib](compiler-builtins-lib.md) - [concat_idents](concat-idents.md) diff --git a/src/doc/unstable-book/src/compiler-barriers.md b/src/doc/unstable-book/src/compiler-fences.md index 827447f0bd5..b1e36ab13d5 100644 --- a/src/doc/unstable-book/src/compiler-barriers.md +++ b/src/doc/unstable-book/src/compiler-fences.md @@ -1,4 +1,4 @@ -# `compiler_barriers` +# `compiler_fences` The tracking issue for this feature is: [#41091] @@ -6,7 +6,7 @@ The tracking issue for this feature is: [#41091] ------------------------ -The `compiler_barriers` feature exposes the `compiler_barrier` function +The `compiler_fences` feature exposes the `compiler_fence` function in `std::sync::atomic`. This function is conceptually similar to C++'s `atomic_signal_fence`, which can currently only be accessed in nightly Rust using the `atomic_singlethreadfence_*` instrinsic functions in @@ -17,18 +17,18 @@ Rust using the `atomic_singlethreadfence_*` instrinsic functions in unsafe { asm!("" ::: "memory" : "volatile") }; ``` -A `compiler_barrier` restricts the kinds of memory re-ordering the +A `compiler_fence` restricts the kinds of memory re-ordering the compiler is allowed to do. Specifically, depending on the given ordering semantics, the compiler may be disallowed from moving reads or writes from before or after the call to the other side of the call to -`compiler_barrier`. Note that it does **not** prevent the *hardware* +`compiler_fence`. Note that it does **not** prevent the *hardware* from doing such re-ordering. This is not a problem in a single-threaded, execution context, but when other threads may modify memory at the same time, stronger synchronization primitives are required. ## Examples -`compiler_barrier` is generally only useful for preventing a thread from +`compiler_fence` is generally only useful for preventing a thread from racing *with itself*. That is, if a given thread is executing one piece of code, and is then interrupted, and starts executing code elsewhere (while still in the same thread, and conceptually still on the same @@ -37,7 +37,7 @@ handler is registered. In more low-level code, such situations can also arise when handling interrupts, when implementing green threads with pre-emption, etc. -To give a straightforward example of when a `compiler_barrier` is +To give a straightforward example of when a `compiler_fence` is necessary, consider the following example: ```rust @@ -67,14 +67,14 @@ remember that the compiler is free to swap the stores to after `IS_READY` is updated, then the signal handler will see `IS_READY=1`, but `IMPORTANT_VARIABLE=0`. -Using a `compiler_barrier`, we can remedy this situation: +Using a `compiler_fence`, we can remedy this situation: ```rust -#![feature(compiler_barriers)] +#![feature(compiler_fences)] # use std::sync::atomic::{AtomicBool, AtomicUsize}; # use std::sync::atomic::{ATOMIC_BOOL_INIT, ATOMIC_USIZE_INIT}; # use std::sync::atomic::Ordering; -use std::sync::atomic::compiler_barrier; +use std::sync::atomic::compiler_fence; static IMPORTANT_VARIABLE: AtomicUsize = ATOMIC_USIZE_INIT; static IS_READY: AtomicBool = ATOMIC_BOOL_INIT; @@ -82,7 +82,7 @@ static IS_READY: AtomicBool = ATOMIC_BOOL_INIT; fn main() { IMPORTANT_VARIABLE.store(42, Ordering::Relaxed); // prevent earlier writes from being moved beyond this point - compiler_barrier(Ordering::Release); + compiler_fence(Ordering::Release); IS_READY.store(true, Ordering::Relaxed); } diff --git a/src/libcore/sync/atomic.rs b/src/libcore/sync/atomic.rs index 0c70524ead2..fad58deecd4 100644 --- a/src/libcore/sync/atomic.rs +++ b/src/libcore/sync/atomic.rs @@ -1591,11 +1591,11 @@ pub fn fence(order: Ordering) { } -/// A compiler memory barrier. +/// A compiler memory fence. /// -/// `compiler_barrier` does not emit any machine code, but prevents the compiler from re-ordering +/// `compiler_fence` does not emit any machine code, but prevents the compiler from re-ordering /// memory operations across this point. Which reorderings are disallowed is dictated by the given -/// [`Ordering`]. Note that `compiler_barrier` does *not* introduce inter-thread memory +/// [`Ordering`]. Note that `compiler_fence` does *not* introduce inter-thread memory /// synchronization; for that, a [`fence`] is needed. /// /// The re-ordering prevented by the different ordering semantics are: @@ -1617,15 +1617,15 @@ pub fn fence(order: Ordering) { /// [`AcqRel`]: enum.Ordering.html#variant.AcqRel /// [`Relaxed`]: enum.Ordering.html#variant.Relaxed #[inline] -#[unstable(feature = "compiler_barriers", issue = "41091")] -pub fn compiler_barrier(order: Ordering) { +#[unstable(feature = "compiler_fences", issue = "41091")] +pub fn compiler_fence(order: Ordering) { unsafe { match order { Acquire => intrinsics::atomic_singlethreadfence_acq(), Release => intrinsics::atomic_singlethreadfence_rel(), AcqRel => intrinsics::atomic_singlethreadfence_acqrel(), SeqCst => intrinsics::atomic_singlethreadfence(), - Relaxed => panic!("there is no such thing as a relaxed barrier"), + Relaxed => panic!("there is no such thing as a relaxed compiler fence"), __Nonexhaustive => panic!("invalid memory ordering"), } } |