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partial.rs
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97 lines (88 loc) · 2.73 KB
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// Copyright 2020 bluss and ndarray developers.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use std::ptr;
/// Partial is a partially written contiguous slice of data;
/// it is the owner of the elements, but not the allocation,
/// and will drop the elements on drop.
#[must_use]
pub(crate) struct Partial<T>
{
/// Data pointer
ptr: *mut T,
/// Current length
pub(crate) len: usize,
}
impl<T> Partial<T>
{
/// Create an empty partial for this data pointer
///
/// ## Safety
///
/// Unless ownership is released, the Partial acts as an owner of the slice of data (not the
/// allocation); and will free the elements on drop; the pointer must be dereferenceable and
/// the `len` elements following it valid.
///
/// The Partial has an accessible length field which must only be modified in trusted code.
pub(crate) unsafe fn new(ptr: *mut T) -> Self
{
Self { ptr, len: 0 }
}
#[cfg(feature = "rayon")]
pub(crate) fn stub() -> Self
{
Self {
len: 0,
ptr: ptr::null_mut(),
}
}
#[cfg(feature = "rayon")]
pub(crate) fn is_stub(&self) -> bool
{
self.ptr.is_null()
}
/// Release Partial's ownership of the written elements, and return the current length
pub(crate) fn release_ownership(mut self) -> usize
{
let ret = self.len;
self.len = 0;
ret
}
#[cfg(feature = "rayon")]
/// Merge if they are in order (left to right) and contiguous.
/// Skips merge if T does not need drop.
pub(crate) fn try_merge(mut left: Self, right: Self) -> Self
{
if !std::mem::needs_drop::<T>() {
return left;
}
// Merge the partial collect results; the final result will be a slice that
// covers the whole output.
if left.is_stub() {
right
} else if left.ptr.wrapping_add(left.len) == right.ptr {
left.len += right.release_ownership();
left
} else {
// failure to merge; this is a bug in collect, so we will never reach this
debug_assert!(false, "Partial: failure to merge left and right parts");
left
}
}
}
unsafe impl<T> Send for Partial<T> where T: Send {}
impl<T> Drop for Partial<T>
{
fn drop(&mut self)
{
if !self.ptr.is_null() {
unsafe {
ptr::drop_in_place(alloc::slice::from_raw_parts_mut(self.ptr, self.len));
}
}
}
}