Struct portable_atomic::AtomicF32

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#[repr(C, align(4))]
pub struct AtomicF32 { /* private fields */ }

Available on crate feature float only.

Expand description

A floating point type which can be safely shared between threads.

This type has the same in-memory representation as the underlying floating point type, f32.

Implementations§

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impl AtomicF32

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pub const fn new(v: f32) -> Self

Creates a new atomic float.

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pub unsafe fn from_ptr<'a>(ptr: *mut f32) -> &'a Self

Creates a new reference to an atomic float from a pointer.

Safety

ptr must be aligned to align_of::<AtomicF32>() (note that on some platforms this can be bigger than align_of::<f32>()).
ptr must be valid for both reads and writes for the whole lifetime 'a.
If this atomic type is lock-free, non-atomic accesses to the value behind ptr must have a happens-before relationship with atomic accesses via the returned value (or vice-versa).
- In other words, time periods where the value is accessed atomically may not overlap with periods where the value is accessed non-atomically.
- This requirement is trivially satisfied if ptr is never used non-atomically for the duration of lifetime 'a. Most use cases should be able to follow this guideline.
- This requirement is also trivially satisfied if all accesses (atomic or not) are done from the same thread.
If this atomic type is not lock-free:
- Any accesses to the value behind ptr must have a happens-before relationship with accesses via the returned value (or vice-versa).
- Any concurrent accesses to the value behind ptr for the duration of lifetime 'a must be compatible with operations performed by this atomic type.
This method must not be used to create overlapping or mixed-size atomic accesses, as these are not supported by the memory model.

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pub fn is_lock_free() -> bool

Returns true if operations on values of this type are lock-free.

If the compiler or the platform doesn’t support the necessary atomic instructions, global locks for every potentially concurrent atomic operation will be used.

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pub const fn is_always_lock_free() -> bool

Returns true if operations on values of this type are lock-free.

If the compiler or the platform doesn’t support the necessary atomic instructions, global locks for every potentially concurrent atomic operation will be used.

Note: If the atomic operation relies on dynamic CPU feature detection, this type may be lock-free even if the function returns false.

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pub fn get_mut(&mut self) -> &mut f32

Returns a mutable reference to the underlying float.

This is safe because the mutable reference guarantees that no other threads are concurrently accessing the atomic data.

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pub fn into_inner(self) -> f32

Consumes the atomic and returns the contained value.

This is safe because passing self by value guarantees that no other threads are concurrently accessing the atomic data.

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pub fn load(&self, order: Ordering) -> f32

Loads a value from the atomic float.

load takes an Ordering argument which describes the memory ordering of this operation. Possible values are SeqCst, Acquire and Relaxed.

Panics

Panics if order is Release or AcqRel.

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pub fn store(&self, val: f32, order: Ordering)

Stores a value into the atomic float.

store takes an Ordering argument which describes the memory ordering of this operation. Possible values are SeqCst, Release and Relaxed.

Panics

Panics if order is Acquire or AcqRel.

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pub fn swap(&self, val: f32, order: Ordering) -> f32

Stores a value into the atomic float, returning the previous value.

swap takes an Ordering argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using Acquire makes the store part of this operation Relaxed, and using Release makes the load part Relaxed.

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pub fn compare_exchange( &self, current: f32, new: f32, success: Ordering, failure: Ordering ) -> Result<f32, f32>

Stores a value into the atomic float if the current value is the same as the current value.

The return value is a result indicating whether the new value was written and containing the previous value. On success this value is guaranteed to be equal to current.

compare_exchange takes two Ordering arguments to describe the memory ordering of this operation. success describes the required ordering for the read-modify-write operation that takes place if the comparison with current succeeds. failure describes the required ordering for the load operation that takes place when the comparison fails. Using Acquire as success ordering makes the store part of this operation Relaxed, and using Release makes the successful load Relaxed. The failure ordering can only be SeqCst, Acquire or Relaxed.

Panics

Panics if failure is Release, AcqRel.

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pub fn compare_exchange_weak( &self, current: f32, new: f32, success: Ordering, failure: Ordering ) -> Result<f32, f32>

Stores a value into the atomic float if the current value is the same as the current value. Unlike compare_exchange this function is allowed to spuriously fail even when the comparison succeeds, which can result in more efficient code on some platforms. The return value is a result indicating whether the new value was written and containing the previous value.

compare_exchange_weak takes two Ordering arguments to describe the memory ordering of this operation. success describes the required ordering for the read-modify-write operation that takes place if the comparison with current succeeds. failure describes the required ordering for the load operation that takes place when the comparison fails. Using Acquire as success ordering makes the store part of this operation Relaxed, and using Release makes the successful load Relaxed. The failure ordering can only be SeqCst, Acquire or Relaxed.

Panics

Panics if failure is Release, AcqRel.

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pub fn fetch_add(&self, val: f32, order: Ordering) -> f32

Adds to the current value, returning the previous value.

This operation wraps around on overflow.

fetch_add takes an Ordering argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using Acquire makes the store part of this operation Relaxed, and using Release makes the load part Relaxed.

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pub fn fetch_sub(&self, val: f32, order: Ordering) -> f32

Subtracts from the current value, returning the previous value.

This operation wraps around on overflow.

fetch_sub takes an Ordering argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using Acquire makes the store part of this operation Relaxed, and using Release makes the load part Relaxed.

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pub fn fetch_update<F>( &self, set_order: Ordering, fetch_order: Ordering, f: F ) -> Result<f32, f32>
where F: FnMut(f32) -> Option<f32>,

Fetches the value, and applies a function to it that returns an optional new value. Returns a Result of Ok(previous_value) if the function returned Some(_), else Err(previous_value).

Note: This may call the function multiple times if the value has been changed from other threads in the meantime, as long as the function returns Some(_), but the function will have been applied only once to the stored value.

fetch_update takes two Ordering arguments to describe the memory ordering of this operation. The first describes the required ordering for when the operation finally succeeds while the second describes the required ordering for loads. These correspond to the success and failure orderings of compare_exchange respectively.

Using Acquire as success ordering makes the store part of this operation Relaxed, and using Release makes the final successful load Relaxed. The (failed) load ordering can only be SeqCst, Acquire or Relaxed.

Panics

Panics if fetch_order is Release, AcqRel.

Considerations

This method is not magic; it is not provided by the hardware. It is implemented in terms of compare_exchange_weak, and suffers from the same drawbacks. In particular, this method will not circumvent the ABA Problem.

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pub fn fetch_max(&self, val: f32, order: Ordering) -> f32

Maximum with the current value.

Finds the maximum of the current value and the argument val, and sets the new value to the result.

Returns the previous value.

fetch_max takes an Ordering argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using Acquire makes the store part of this operation Relaxed, and using Release makes the load part Relaxed.

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pub fn fetch_min(&self, val: f32, order: Ordering) -> f32

Minimum with the current value.

Finds the minimum of the current value and the argument val, and sets the new value to the result.

Returns the previous value.

fetch_min takes an Ordering argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using Acquire makes the store part of this operation Relaxed, and using Release makes the load part Relaxed.

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pub fn fetch_neg(&self, order: Ordering) -> f32

Negates the current value, and sets the new value to the result.

Returns the previous value.

fetch_neg takes an Ordering argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using Acquire makes the store part of this operation Relaxed, and using Release makes the load part Relaxed.

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pub fn fetch_abs(&self, order: Ordering) -> f32

Computes the absolute value of the current value, and sets the new value to the result.

Returns the previous value.

fetch_abs takes an Ordering argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using Acquire makes the store part of this operation Relaxed, and using Release makes the load part Relaxed.

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pub const fn as_bits(&self) -> &AtomicU32

Raw transmutation to &AtomicU32.

See f32::from_bits for some discussion of the portability of this operation (there are almost no issues).

This is const fn on Rust 1.58+.

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pub const fn as_ptr(&self) -> *mut f32

Returns a mutable pointer to the underlying float.

Returning an *mut pointer from a shared reference to this atomic is safe because the atomic types work with interior mutability. Any use of the returned raw pointer requires an unsafe block and has to uphold the safety requirements. If there is concurrent access, note the following additional safety requirements:

If this atomic type is lock-free, any concurrent operations on it must be atomic.
Otherwise, any concurrent operations on it must be compatible with operations performed by this atomic type.

This is const fn on Rust 1.58+.