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| 1 | +// SPDX-License-Identifier: Apache-2.0 OR MIT |
| 2 | + |
| 3 | +#[cfg(all(feature = "alloc", not(feature = "std")))] |
| 4 | +use alloc::{boxed::Box, sync::Arc}; |
| 5 | +#[cfg(feature = "alloc")] |
| 6 | +use core::alloc::AllocError; |
| 7 | +use core::{mem::MaybeUninit, pin::Pin}; |
| 8 | +#[cfg(feature = "std")] |
| 9 | +use std::sync::Arc; |
| 10 | + |
| 11 | +#[cfg(not(feature = "alloc"))] |
| 12 | +type AllocError = core::convert::Infallible; |
| 13 | + |
| 14 | +use crate::{ |
| 15 | + init_from_closure, pin_init_from_closure, InPlaceWrite, Init, PinInit, ZeroableOption, |
| 16 | +}; |
| 17 | + |
| 18 | +pub extern crate alloc; |
| 19 | + |
| 20 | +// SAFETY: All zeros is equivalent to `None` (option layout optimization guarantee). |
| 21 | +// |
| 22 | +// In this case we are allowed to use `T: ?Sized`, since all zeros is the `None` variant and there |
| 23 | +// is no problem with a VTABLE pointer being null. |
| 24 | +unsafe impl<T: ?Sized> ZeroableOption for Box<T> {} |
| 25 | + |
| 26 | +/// Smart pointer that can initialize memory in-place. |
| 27 | +pub trait InPlaceInit<T>: Sized { |
| 28 | + /// Use the given pin-initializer to pin-initialize a `T` inside of a new smart pointer of this |
| 29 | + /// type. |
| 30 | + /// |
| 31 | + /// If `T: !Unpin` it will not be able to move afterwards. |
| 32 | + fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> |
| 33 | + where |
| 34 | + E: From<AllocError>; |
| 35 | + |
| 36 | + /// Use the given pin-initializer to pin-initialize a `T` inside of a new smart pointer of this |
| 37 | + /// type. |
| 38 | + /// |
| 39 | + /// If `T: !Unpin` it will not be able to move afterwards. |
| 40 | + fn pin_init(init: impl PinInit<T>) -> Result<Pin<Self>, AllocError> { |
| 41 | + // SAFETY: We delegate to `init` and only change the error type. |
| 42 | + let init = unsafe { |
| 43 | + pin_init_from_closure(|slot| match init.__pinned_init(slot) { |
| 44 | + Ok(()) => Ok(()), |
| 45 | + Err(i) => match i {}, |
| 46 | + }) |
| 47 | + }; |
| 48 | + Self::try_pin_init(init) |
| 49 | + } |
| 50 | + |
| 51 | + /// Use the given initializer to in-place initialize a `T`. |
| 52 | + fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E> |
| 53 | + where |
| 54 | + E: From<AllocError>; |
| 55 | + |
| 56 | + /// Use the given initializer to in-place initialize a `T`. |
| 57 | + fn init(init: impl Init<T>) -> Result<Self, AllocError> { |
| 58 | + // SAFETY: We delegate to `init` and only change the error type. |
| 59 | + let init = unsafe { |
| 60 | + init_from_closure(|slot| match init.__init(slot) { |
| 61 | + Ok(()) => Ok(()), |
| 62 | + Err(i) => match i {}, |
| 63 | + }) |
| 64 | + }; |
| 65 | + Self::try_init(init) |
| 66 | + } |
| 67 | +} |
| 68 | + |
| 69 | +#[cfg(feature = "alloc")] |
| 70 | +macro_rules! try_new_uninit { |
| 71 | + ($type:ident) => { |
| 72 | + $type::try_new_uninit()? |
| 73 | + }; |
| 74 | +} |
| 75 | +#[cfg(all(feature = "std", not(feature = "alloc")))] |
| 76 | +macro_rules! try_new_uninit { |
| 77 | + ($type:ident) => { |
| 78 | + $type::new_uninit() |
| 79 | + }; |
| 80 | +} |
| 81 | + |
| 82 | +impl<T> InPlaceInit<T> for Box<T> { |
| 83 | + #[inline] |
| 84 | + fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> |
| 85 | + where |
| 86 | + E: From<AllocError>, |
| 87 | + { |
| 88 | + try_new_uninit!(Box).write_pin_init(init) |
| 89 | + } |
| 90 | + |
| 91 | + #[inline] |
| 92 | + fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E> |
| 93 | + where |
| 94 | + E: From<AllocError>, |
| 95 | + { |
| 96 | + try_new_uninit!(Box).write_init(init) |
| 97 | + } |
| 98 | +} |
| 99 | + |
| 100 | +impl<T> InPlaceInit<T> for Arc<T> { |
| 101 | + #[inline] |
| 102 | + fn try_pin_init<E>(init: impl PinInit<T, E>) -> Result<Pin<Self>, E> |
| 103 | + where |
| 104 | + E: From<AllocError>, |
| 105 | + { |
| 106 | + let mut this = try_new_uninit!(Arc); |
| 107 | + let Some(slot) = Arc::get_mut(&mut this) else { |
| 108 | + // SAFETY: the Arc has just been created and has no external references |
| 109 | + unsafe { core::hint::unreachable_unchecked() } |
| 110 | + }; |
| 111 | + let slot = slot.as_mut_ptr(); |
| 112 | + // SAFETY: When init errors/panics, slot will get deallocated but not dropped, |
| 113 | + // slot is valid and will not be moved, because we pin it later. |
| 114 | + unsafe { init.__pinned_init(slot)? }; |
| 115 | + // SAFETY: All fields have been initialized and this is the only `Arc` to that data. |
| 116 | + Ok(unsafe { Pin::new_unchecked(this.assume_init()) }) |
| 117 | + } |
| 118 | + |
| 119 | + #[inline] |
| 120 | + fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E> |
| 121 | + where |
| 122 | + E: From<AllocError>, |
| 123 | + { |
| 124 | + let mut this = try_new_uninit!(Arc); |
| 125 | + let Some(slot) = Arc::get_mut(&mut this) else { |
| 126 | + // SAFETY: the Arc has just been created and has no external references |
| 127 | + unsafe { core::hint::unreachable_unchecked() } |
| 128 | + }; |
| 129 | + let slot = slot.as_mut_ptr(); |
| 130 | + // SAFETY: When init errors/panics, slot will get deallocated but not dropped, |
| 131 | + // slot is valid. |
| 132 | + unsafe { init.__init(slot)? }; |
| 133 | + // SAFETY: All fields have been initialized. |
| 134 | + Ok(unsafe { this.assume_init() }) |
| 135 | + } |
| 136 | +} |
| 137 | + |
| 138 | +impl<T> InPlaceWrite<T> for Box<MaybeUninit<T>> { |
| 139 | + type Initialized = Box<T>; |
| 140 | + |
| 141 | + fn write_init<E>(mut self, init: impl Init<T, E>) -> Result<Self::Initialized, E> { |
| 142 | + let slot = self.as_mut_ptr(); |
| 143 | + // SAFETY: When init errors/panics, slot will get deallocated but not dropped, |
| 144 | + // slot is valid. |
| 145 | + unsafe { init.__init(slot)? }; |
| 146 | + // SAFETY: All fields have been initialized. |
| 147 | + Ok(unsafe { self.assume_init() }) |
| 148 | + } |
| 149 | + |
| 150 | + fn write_pin_init<E>(mut self, init: impl PinInit<T, E>) -> Result<Pin<Self::Initialized>, E> { |
| 151 | + let slot = self.as_mut_ptr(); |
| 152 | + // SAFETY: When init errors/panics, slot will get deallocated but not dropped, |
| 153 | + // slot is valid and will not be moved, because we pin it later. |
| 154 | + unsafe { init.__pinned_init(slot)? }; |
| 155 | + // SAFETY: All fields have been initialized. |
| 156 | + Ok(unsafe { self.assume_init() }.into()) |
| 157 | + } |
| 158 | +} |
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