vulkano 0.32.3

// Copyright (c) 2016 The vulkano developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or https://opensource.org/licenses/MIT>,
// at your option. All files in the project carrying such
// notice may not be copied, modified, or distributed except
// according to those terms.

//! In Vulkan, suballocation of [`DeviceMemory`] is left to the application, because every
//! application has slightly different needs and one can not incorporate an allocator into the
//! driver that would perform well in all cases. Vulkano stays true to this sentiment, but aims to
//! reduce the burden on the user as much as possible. You have a toolbox of configurable
//! [suballocators] to choose from that cover all allocation algorithms, which you can compose into
//! any kind of [hierarchy] you wish. This way you have maximum flexibility while still only using
//! a few `DeviceMemory` blocks and not writing any of the very error-prone code.
//!
//! If you just want to allocate memory and don't have any special needs, look no further than the
//! [`StandardMemoryAllocator`].
//!
//! # Why not just allocate `DeviceMemory`?
//!
//! But the driver has an allocator! Otherwise you wouldn't be able to allocate `DeviceMemory`,
//! right? Indeed, but that allocation is very expensive. Not only that, there is also a pretty low
//! limit on the number of allocations by the drivers. See, everything in Vulkan tries to keep you
//! away from allocating `DeviceMemory` too much. These limits are used by the implementation to
//! optimize on its end, while the application optimizes on the other end.
//!
//! # Alignment
//!
//! At the end of the day, memory needs to be backed by hardware somehow. A *memory cell* stores a
//! single *bit*, bits are grouped into *bytes* and bytes are grouped into *words*. Intuitively, it
//! should make sense that accessing single bits at a time would be very inefficient. That is why
//! computers always access a whole word of memory at once, at least. That means that if you tried
//! to do an unaligned access, you would need to access twice the number of memory locations.
//!
//! Example aligned access, performing bitwise NOT on the (64-bit) word at offset 0x08:
//!
//! ```plain
//!     | 08                      | 10                      | 18
//! ----+-------------------------+-------------------------+----
//! ••• | 35 35 35 35 35 35 35 35 | 01 23 45 67 89 ab cd ef | •••
//! ----+-------------------------+-------------------------+----
//!     ,            |            ,
//!     +------------|------------+
//!     '            v            '
//! ----+-------------------------+-------------------------+----
//! ••• | ca ca ca ca ca ca ca ca | 01 23 45 67 89 ab cd ef | •••
//! ----+-------------------------+-------------------------+----
//! ```
//!
//! Same example as above, but this time unaligned with a word at offset 0x0a:
//!
//! ```plain
//!     | 08    0a                | 10                      | 18
//! ----+-------------------------+-------------------------+----
//! ••• | cd ef 35 35 35 35 35 35 | 35 35 01 23 45 67 89 ab | •••
//! ----+-------------------------+-------------------------+----
//!            ,            |            ,
//!            +------------|------------+
//!            '            v            '
//! ----+-------------------------+-------------------------+----
//! ••• | cd ef ca ca ca ca ca ca | ca ca 01 23 45 67 89 ab | •••
//! ----+-------------------------+-------------------------+----
//! ```
//!
//! As you can see, in the unaligned case the hardware would need to read both the word at offset
//! 0x08 and the word at the offset 0x10 and then shift the bits from one register into the other.
//! Safe to say it should to be avoided, and this is why we need alignment. This example also goes
//! to show how inefficient unaligned writes are. Say you pieced together your word as described,
//! and now you want to perform the bitwise NOT and write the result back. Difficult, isn't it?
//! That's due to the fact that even though the chunks occupy different ranges in memory, they are
//! still said to *alias* each other, because if you try to write to one memory location, you would
//! be overwriting 2 or more different chunks of data.
//!
//! ## Pages
//!
//! It doesn't stop at the word, though. Words are further grouped into *pages*. These are
//! typically power-of-two multiples of the word size, much like words are typically powers of two
//! themselves. You can easily extend the concepts from the previous examples to pages if you think
//! of the examples as having a page size of 1 word. Two resources are said to alias if they share
//! a page, and therefore should be aligned to the page size. What the page size is depends on the
//! context, and a computer might have multiple different ones for different parts of hardware.
//!
//! ## Memory requirements
//!
//! A Vulkan device might have any number of reasons it would want certain alignments for certain
//! resources. For example, the device might have different caches for different types of
//! resources, which have different page sizes. Maybe the device wants to store images in some
//! other cache compared to buffers which needs different alignment. Or maybe images of different
//! layouts require different alignment, or buffers with different usage/mapping do. The specifics
//! don't matter in the end, this just goes to illustrate the point. This is why memory
//! requirements in Vulkan vary not only with the Vulkan implementation, but also with the type of
//! resource.
//!
//! ## Buffer-image granularity
//!
//! This unfortunately named granularity is the page size which a linear resource neighboring a
//! non-linear resource must be aligned to in order for them not to alias. The difference between
//! the memory requirements of the individual resources and the [buffer-image granularity] is that
//! the memory requirements only apply to the resource they are for, while the buffer-image
//! granularity applies to two neighboring resources. For example, you might create two buffers,
//! which might have two different memory requirements, but as long as those are satisfied, you can
//! put these buffers cheek to cheek. On the other hand, if one of them is an (optimal layout)
//! image, then they must not share any page, whose size is given by this granularity. The Vulkan
//! implementation can use this for additional optimizations if it needs to, or report a
//! granularity of 1.
//!
//! # Fragmentation
//!
//! Memory fragmentation refers to the wastage of memory that results from alignment requirements
//! and/or dynamic memory allocation. As such, some level of fragmentation is always going to be
//! inevitable. Different allocation algorithms each have their own characteristics and trade-offs
//! in relation to fragmentation.
//!
//! ## Internal Fragmentation
//!
//! This type of fragmentation arises from alignment requirements. These might be imposed by the
//! Vulkan implementation or the application itself.
//!
//! Say for example your allocations need to be aligned to 64B, then any allocation whose size is
//! not a multiple of the alignment will need padding at the end:
//!
//! ```plain
//!     | 0x040            | 0x080            | 0x0c0            | 0x100
//! ----+------------------+------------------+------------------+--------
//!     | ############     | ################ | ########         | #######
//! ••• | ### 48 B ###     | ##### 64 B ##### | # 32 B #         | ### •••
//!     | ############     | ################ | ########         | #######
//! ----+------------------+------------------+------------------+--------
//! ```
//!
//! If this alignment is imposed by the Vulkan implementation, then there's nothing one can do
//! about this. Simply put, that space is unusable. One also shouldn't want to do anything about
//! it, since these requirements have very good reasons, as described in further detail in previous
//! sections. They prevent resources from aliasing so that performance is optimal.
//!
//! It might seem strange that the application would want to cause internal fragmentation itself,
//! but this is often a good trade-off to reduce or even completely eliminate external
//! fragmentation. Internal fragmentation is very predictable, which makes it easier to deal with.
//!
//! ## External fragmentation
//!
//! With external fragmentation, what happens is that while the allocations might be using their
//! own memory totally efficiently, the way they are arranged in relation to each other would
//! prevent a new contiguous chunk of memory to be allocated even though there is enough free space
//! left. That is why this fragmentation is said to be external to the allocations. Also, the
//! allocations together with the fragments in-between add overhead both in terms of space and time
//! to the allocator, because it needs to keep track of more things overall.
//!
//! As an example, take these 4 allocations within some block, with the rest of the block assumed
//! to be full:
//!
//! ```plain
//! +-----+-------------------+-------+-----------+-- - - --+
//! |     |                   |       |           |         |
//! |  A  |         B         |   C   |     D     |   •••   |
//! |     |                   |       |           |         |
//! +-----+-------------------+-------+-----------+-- - - --+
//! ```
//!
//! The allocations were all done in order, and naturally there is no fragmentation at this point.
//! Now if we free B and D, since these are done out of order, we will be left with holes between
//! the other allocations, and we won't be able to fit allocation E anywhere:
//!
//!  ```plain
//! +-----+-------------------+-------+-----------+-- - - --+       +-------------------------+
//! |     |                   |       |           |         |   ?   |                         |
//! |  A  |                   |   C   |           |   •••   |  <==  |            E            |
//! |     |                   |       |           |         |       |                         |
//! +-----+-------------------+-------+-----------+-- - - --+       +-------------------------+
//! ```
//!
//! So fine, we use a different block for E, and just use this block for allocations that fit:
//!
//! ```plain
//! +-----+---+-----+---------+-------+-----+-----+-- - - --+
//! |     |   |     |         |       |     |     |         |
//! |  A  | H |  I  |    J    |   C   |  F  |  G  |   •••   |
//! |     |   |     |         |       |     |     |         |
//! +-----+---+-----+---------+-------+-----+-----+-- - - --+
//! ```
//!
//! Sure, now let's free some shall we? And voilà, the problem just became much worse:
//!
//! ```plain
//! +-----+---+-----+---------+-------+-----+-----+-- - - --+
//! |     |   |     |         |       |     |     |         |
//! |  A  |   |  I  |    J    |       |  F  |     |   •••   |
//! |     |   |     |         |       |     |     |         |
//! +-----+---+-----+---------+-------+-----+-----+-- - - --+
//! ```
//!
//! # Leakage
//!
//! Memory leaks happen when allocations are kept alive past their shelf life. This most often
//! occurs because of [cyclic references]. If you have structures that have cycles, then make sure
//! you read the documentation for [`Arc`]/[`Rc`] carefully to avoid memory leaks. You can also
//! introduce memory leaks willingly by using [`mem::forget`] or [`Box::leak`] to name a few. In
//! all of these examples the memory can never be reclaimed, but that doesn't have to be the case
//! for something to be considered a leak. Say for example you have a [region] which you
//! suballocate, and at some point you drop all the suballocations. When that happens, the region
//! can be returned (freed) to the next level up the hierarchy, or it can be reused by another
//! suballocator. But if you happen to keep alive just one suballocation for the duration of the
//! program for instance, then the whole region is also kept as it is for that time (and keep in
//! mind this bubbles up the hierarchy). Therefore, for the program, that memory might be a leak
//! depending on the allocator, because some allocators wouldn't be able to reuse the entire rest
//! of the region. You must always consider the lifetime of your resources when choosing the
//! appropriate allocator.
//!
//! [suballocators]: Suballocator
//! [hierarchy]: Suballocator#memory-hierarchies
//! [buffer-image granularity]: crate::device::Properties::buffer_image_granularity
//! [cyclic references]: Arc#breaking-cycles-with-weak
//! [`Rc`]: std::rc::Rc
//! [`mem::forget`]: std::mem::forget
//! [region]: Suballocator#regions

pub mod suballocator;

use self::array_vec::ArrayVec;
pub use self::suballocator::{
    AllocationType, BuddyAllocator, BumpAllocator, FreeListAllocator, MemoryAlloc, PoolAllocator,
    SuballocationCreateInfo, SuballocationCreationError, Suballocator,
};
use super::{
    DedicatedAllocation, DeviceMemory, ExternalMemoryHandleTypes, MemoryAllocateFlags,
    MemoryAllocateInfo, MemoryProperties, MemoryPropertyFlags, MemoryRequirements, MemoryType,
};
use crate::{
    device::{Device, DeviceOwned},
    DeviceSize, RequirementNotMet, RequiresOneOf, Version, VulkanError,
};
use ash::vk::{MAX_MEMORY_HEAPS, MAX_MEMORY_TYPES};
use parking_lot::RwLock;
use std::{
    error::Error,
    fmt::{Display, Error as FmtError, Formatter},
    sync::Arc,
};

const B: DeviceSize = 1;
const K: DeviceSize = 1024 * B;
const M: DeviceSize = 1024 * K;
const G: DeviceSize = 1024 * M;

/// General-purpose memory allocators which allocate from any memory type dynamically as needed.
pub unsafe trait MemoryAllocator: DeviceOwned {
    /// Finds the most suitable memory type index in `memory_type_bits` using a filter. Returns
    /// [`None`] if the requirements are too strict and no memory type is able to satisfy them.
    fn find_memory_type_index(
        &self,
        memory_type_bits: u32,
        filter: MemoryTypeFilter,
    ) -> Option<u32>;

    /// Allocates memory from a specific memory type.
    fn allocate_from_type(
        &self,
        memory_type_index: u32,
        create_info: SuballocationCreateInfo,
    ) -> Result<MemoryAlloc, AllocationCreationError>;

    /// Allocates memory from a specific memory type without checking the parameters.
    ///
    /// # Safety
    ///
    /// - If `memory_type_index` refers to a memory type with the [`protected`] flag set, then the
    ///   [`protected_memory`] feature must be enabled on the device.
    /// - If `memory_type_index` refers to a memory type with the [`device_coherent`] flag set,
    ///   then the [`device_coherent_memory`] feature must be enabled on the device.
    /// - `create_info.size` must not be zero.
    /// - `create_info.size` must not exceed the size of the heap that the memory type
    ///   corresponding to `memory_type_index` resides in.
    /// - `create_info.alignment` must not be zero.
    /// - `create_info.alignment` must be a power of two.
    ///
    /// [`protected`]: MemoryPropertyFlags::protected
    /// [`protected_memory`]: crate::device::Features::protected_memory
    /// [`device_coherent`]: MemoryPropertyFlags::device_coherent
    /// [`device_coherent_memory`]: crate::device::Features::device_coherent_memory
    #[cfg_attr(not(feature = "document_unchecked"), doc(hidden))]
    unsafe fn allocate_from_type_unchecked(
        &self,
        memory_type_index: u32,
        create_info: SuballocationCreateInfo,
        never_allocate: bool,
    ) -> Result<MemoryAlloc, AllocationCreationError>;

    /// Allocates memory according to requirements.
    fn allocate(
        &self,
        create_info: AllocationCreateInfo<'_>,
    ) -> Result<MemoryAlloc, AllocationCreationError>;

    /// Allocates memory according to requirements without checking the parameters.
    ///
    /// # Safety
    ///
    /// - `create_info.requirements.size` must not be zero.
    /// - `create_info.requirements.alignment` must not be zero.
    /// - `create_info.requirements.alignment` must be a power of two.
    /// - If `create_info.dedicated_allocation` is `Some` then `create_info.requirements.size` must
    ///   match the memory requirements of the resource.
    /// - If `create_info.dedicated_allocation` is `Some` then the device the resource was created
    ///   with must match the device the allocator was created with.
    #[cfg_attr(not(feature = "document_unchecked"), doc(hidden))]
    unsafe fn allocate_unchecked(
        &self,
        create_info: AllocationCreateInfo<'_>,
    ) -> Result<MemoryAlloc, AllocationCreationError>;

    /// Creates a root allocation/dedicated allocation without checking the parameters.
    ///
    /// # Safety
    ///
    /// - `allocation_size` must not exceed the size of the heap that the memory type corresponding
    ///   to `memory_type_index` resides in.
    /// - The handle types in `export_handle_types` must be supported and compatible, as reported by
    ///   [`ExternalBufferProperties`] or [`ImageFormatProperties`].
    /// - If any of the handle types in `export_handle_types` require a dedicated allocation, as
    ///   reported by [`ExternalBufferProperties::external_memory_properties`] or
    ///   [`ImageFormatProperties::external_memory_properties`], then `dedicated_allocation` must
    ///   not be `None`.
    ///
    /// [`ExternalBufferProperties`]: crate::buffer::ExternalBufferProperties
    /// [`ImageFormatProperties`]: crate::image::ImageFormatProperties
    /// [`ExternalBufferProperties::external_memory_properties`]: crate::buffer::ExternalBufferProperties
    /// [`ImageFormatProperties::external_memory_properties`]: crate::image::ImageFormatProperties::external_memory_properties
    #[cfg_attr(not(feature = "document_unchecked"), doc(hidden))]
    unsafe fn allocate_dedicated_unchecked(
        &self,
        memory_type_index: u32,
        allocation_size: DeviceSize,
        dedicated_allocation: Option<DedicatedAllocation<'_>>,
        export_handle_types: ExternalMemoryHandleTypes,
    ) -> Result<MemoryAlloc, AllocationCreationError>;
}

/// Describes what memory property flags are required, preferred and not preferred when picking a
/// memory type index.
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub struct MemoryTypeFilter {
    pub required_flags: MemoryPropertyFlags,
    pub preferred_flags: MemoryPropertyFlags,
    pub not_preferred_flags: MemoryPropertyFlags,
}

impl From<MemoryUsage> for MemoryTypeFilter {
    #[inline]
    fn from(usage: MemoryUsage) -> Self {
        let mut filter = Self::default();

        match usage {
            MemoryUsage::GpuOnly => {
                filter.preferred_flags.device_local = true;
                filter.not_preferred_flags.host_visible = true;
            }
            MemoryUsage::Upload => {
                filter.required_flags.host_visible = true;
                filter.preferred_flags.device_local = true;
                filter.not_preferred_flags.host_cached = true;
            }
            MemoryUsage::Download => {
                filter.required_flags.host_visible = true;
                filter.preferred_flags.host_cached = true;
            }
        }

        filter
    }
}

/// Parameters to create a new [allocation] using a [memory allocator].
///
/// [allocation]: MemoryAlloc
/// [memory allocator]: MemoryAllocator
#[derive(Clone, Debug)]
pub struct AllocationCreateInfo<'d> {
    /// Requirements of the resource you want to allocate memory for.
    ///
    /// If you plan to bind this memory directly to a non-sparse resource, then this must
    /// correspond to the value returned by either [`RawBuffer::memory_requirements`] or
    /// [`RawImage::memory_requirements`] for the respective buffer or image.
    ///
    /// All of the fields must be non-zero, [`alignment`] must be a power of two, and
    /// [`memory_type_bits`] must be below 2<sup>*n*</sup> where *n* is the number of available
    /// memory types.
    ///
    /// The default is all zeros, which must be overridden.
    ///
    /// [`alignment`]: MemoryRequirements::alignment
    /// [`memory_type_bits`]: MemoryRequirements::memory_type_bits
    /// [`RawBuffer::memory_requirements`]: crate::buffer::sys::RawBuffer::memory_requirements
    /// [`RawImage::memory_requirements`]: crate::image::sys::RawImage::memory_requirements
    pub requirements: MemoryRequirements,

    /// What type of resource this allocation will be used for.
    ///
    /// This should be [`Linear`] for buffers and linear images, and [`NonLinear`] for optimal
    /// images. You can not bind memory allocated with the [`Linear`] type to optimal images or
    /// bind memory allocated with the [`NonLinear`] type to buffers and linear images. You should
    /// never use the [`Unknown`] type unless you have to, as that can be less memory efficient.
    ///
    /// The default value is [`AllocationType::Unknown`].
    ///
    /// [`Linear`]: AllocationType::Linear
    /// [`NonLinear`]: AllocationType::NonLinear
    /// [`Unknown`]: AllocationType::Unknown
    pub allocation_type: AllocationType,

    /// The intended usage for the allocation.
    ///
    /// The default value is [`MemoryUsage::GpuOnly`].
    pub usage: MemoryUsage,

    /// How eager the allocator should be to allocate [`DeviceMemory`].
    ///
    /// The default value is [`MemoryAllocatePreference::Unknown`].
    pub allocate_preference: MemoryAllocatePreference,

    /// Allows a dedicated allocation to be created.
    ///
    /// You should always fill this field in if you are allocating memory for a non-sparse
    /// resource, otherwise the allocator won't be able to create a dedicated allocation if one is
    /// recommended.
    ///
    /// This option is silently ignored (treated as `None`) if the device API version is below 1.1
    /// and the [`khr_dedicated_allocation`] extension is not enabled on the device.
    ///
    /// The default value is [`None`].
    ///
    /// [`khr_dedicated_allocation`]: crate::device::DeviceExtensions::khr_dedicated_allocation
    pub dedicated_allocation: Option<DedicatedAllocation<'d>>,

    pub _ne: crate::NonExhaustive,
}

impl Default for AllocationCreateInfo<'_> {
    #[inline]
    fn default() -> Self {
        AllocationCreateInfo {
            requirements: MemoryRequirements {
                size: 0,
                alignment: 0,
                memory_type_bits: 0,
                prefers_dedicated_allocation: false,
                requires_dedicated_allocation: false,
            },
            allocation_type: AllocationType::Unknown,
            usage: MemoryUsage::GpuOnly,
            allocate_preference: MemoryAllocatePreference::Unknown,
            dedicated_allocation: None,
            _ne: crate::NonExhaustive(()),
        }
    }
}

/// Describes how a memory allocation is going to be used.
///
/// This is mostly an optimization, except for `MemoryUsage::GpuOnly` which will pick a memory type
/// that is not CPU-accessible if such a type exists.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum MemoryUsage {
    /// The memory is intended to only be used by the GPU.
    ///
    /// Prefers picking a memory type with the [`device_local`] flag and without the
    /// [`host_visible`] flag.
    ///
    /// This option is what you will always want to use unless the memory needs to be accessed by
    /// the CPU, because a memory type that can only be accessed by the GPU is going to give the
    /// best performance. Example use cases would be textures and other maps which are written to
    /// once and then never again, or resources that are only written and read by the GPU, like
    /// render targets and intermediary buffers.
    ///
    /// [`device_local`]: MemoryPropertyFlags::device_local
    /// [`host_visible`]: MemoryPropertyFlags::host_visible
    GpuOnly,

    /// The memory is intended for upload to the GPU.
    ///
    /// Guarantees picking a memory type with the [`host_visible`] flag. Prefers picking one
    /// without the [`host_cached`] flag and with the [`device_local`] flag.
    ///
    /// This option is best suited for resources that need to be constantly updated by the CPU,
    /// like vertex and index buffers for example. It is also neccessary for *staging buffers*,
    /// whose only purpose in life it is to get data into `device_local` memory or texels into an
    /// optimal image.
    ///
    /// [`host_visible`]: MemoryPropertyFlags::host_visible
    /// [`host_cached`]: MemoryPropertyFlags::host_cached
    /// [`device_local`]: MemoryPropertyFlags::device_local
    Upload,

    /// The memory is intended for download from the GPU.
    ///
    /// Guarantees picking a memory type with the [`host_visible`] flag. Prefers picking one with
    /// the [`host_cached`] flag and without the [`device_local`] flag.
    ///
    /// This option is best suited if you're using the GPU for things other than rendering and you
    /// need to get the results back to the CPU. That might be compute shading, or image or video
    /// manipulation, or screenshotting for example.
    ///
    /// [`host_visible`]: MemoryPropertyFlags::host_visible
    /// [`host_cached`]: MemoryPropertyFlags::host_cached
    /// [`device_local`]: MemoryPropertyFlags::device_local
    Download,
}

/// Describes whether allocating [`DeviceMemory`] is desired.
#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
pub enum MemoryAllocatePreference {
    /// There is no known preference, let the allocator decide.
    Unknown,

    /// The allocator should never allocate `DeviceMemory` and should instead only suballocate from
    /// existing blocks.
    ///
    /// This option is best suited if you can not afford the overhead of allocating `DeviceMemory`.
    NeverAllocate,

    /// The allocator should always allocate `DeviceMemory`.
    ///
    /// This option is best suited if you are allocating a long-lived resource that you know could
    /// benefit from having a dedicated allocation.
    AlwaysAllocate,
}

/// Error that can be returned when creating an [allocation] using a [memory allocator].
///
/// [allocation]: MemoryAlloc
/// [memory allocator]: MemoryAllocator
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum AllocationCreationError {
    VulkanError(VulkanError),

    /// There is not enough memory in the pool.
    ///
    /// This is returned when using [`MemoryAllocatePreference::NeverAllocate`] and there is not
    /// enough memory in the pool.
    OutOfPoolMemory,

    /// A dedicated allocation is required but was explicitly forbidden.
    ///
    /// This is returned when using [`MemoryAllocatePreference::NeverAllocate`] and the
    /// implementation requires a dedicated allocation.
    DedicatedAllocationRequired,

    /// The block size for the allocator was exceeded.
    ///
    /// This is returned when using [`MemoryAllocatePreference::NeverAllocate`] and the allocation
    /// size exceeded the block size for all heaps of suitable memory types.
    BlockSizeExceeded,

    /// The block size for the suballocator was exceeded.
    ///
    /// This is returned when using [`GenericMemoryAllocator<Arc<PoolAllocator<BLOCK_SIZE>>>`] if
    /// the allocation size exceeded `BLOCK_SIZE`.
    SuballocatorBlockSizeExceeded,
}

impl Error for AllocationCreationError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        match self {
            Self::VulkanError(err) => Some(err),
            _ => None,
        }
    }
}

impl Display for AllocationCreationError {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), FmtError> {
        match self {
            Self::VulkanError(_) => write!(f, "a runtime error occurred"),
            Self::OutOfPoolMemory => write!(f, "the pool doesn't have enough free space"),
            Self::DedicatedAllocationRequired => write!(
                f,
                "a dedicated allocation is required but was explicitly forbidden",
            ),
            Self::BlockSizeExceeded => write!(
                f,
                "the allocation size was greater than the block size for all heaps of suitable \
                memory types and dedicated allocations were explicitly forbidden",
            ),
            Self::SuballocatorBlockSizeExceeded => write!(
                f,
                "the allocation size was greater than the suballocator's block size",
            ),
        }
    }
}

impl From<VulkanError> for AllocationCreationError {
    fn from(err: VulkanError) -> Self {
        AllocationCreationError::VulkanError(err)
    }
}

/// Standard memory allocator intended as a global and general-purpose allocator.
///
/// This type of allocator should work well in most cases, it is however **not** to be used when
/// allocations need to be made very frequently (say, once or more per frame). For that purpose,
/// use [`FastMemoryAllocator`].
///
/// See [`FreeListAllocator`] for details about the allocation algorithm and example usage.
pub type StandardMemoryAllocator = GenericMemoryAllocator<Arc<FreeListAllocator>>;

impl StandardMemoryAllocator {
    /// Creates a new `StandardMemoryAllocator` with default configuration.
    pub fn new_default(device: Arc<Device>) -> Self {
        #[allow(clippy::erasing_op, clippy::identity_op)]
        let create_info = GenericMemoryAllocatorCreateInfo {
            #[rustfmt::skip]
            block_sizes: &[
                (0 * B,  64 * M),
                (1 * G, 256 * M),
            ],
            ..Default::default()
        };

        unsafe { Self::new_unchecked(device, create_info) }
    }
}

/// Fast memory allocator intended as a local and special-purpose allocator.
///
/// This type of allocator is only useful when you need to allocate a lot, for example once or more
/// per frame. It is **not** to be used when allocations are long-lived. For that purpose use
/// [`StandardMemoryAllocator`].
///
/// See [`BumpAllocator`] for details about the allocation algorithm.
pub type FastMemoryAllocator = GenericMemoryAllocator<Arc<BumpAllocator>>;

impl FastMemoryAllocator {
    /// Creates a new `FastMemoryAllocator` with default configuration.
    pub fn new_default(device: Arc<Device>) -> Self {
        #[allow(clippy::erasing_op, clippy::identity_op)]
        let create_info = GenericMemoryAllocatorCreateInfo {
            #[rustfmt::skip]
            block_sizes: &[
                (  0 * B, 16 * M),
                (512 * M, 32 * M),
                (  1 * G, 64 * M),
            ],
            ..Default::default()
        };

        unsafe { Self::new_unchecked(device, create_info) }
    }
}

/// A generic implementation of a [memory allocator].
///
/// The allocator keeps a pool of [`DeviceMemory`] blocks for each memory type and uses the type
/// parameter `S` to [suballocate] these blocks. You can also configure the sizes of these blocks.
/// This means that you can have as many `GenericMemoryAllocator`s as you you want for different
/// needs, or for performance reasons, as long as the block sizes are configured properly so that
/// too much memory isn't wasted.
///
/// See also [the `MemoryAllocator` implementation].
///
/// # `DeviceMemory` allocation
///
/// If an allocation is created with the [`MemoryAllocatePreference::Unknown`] option, and the
/// allocator deems the allocation too big for suballocation (larger than half the block size), or
/// the implementation prefers or requires a dedicated allocation, then that allocation is made a
/// dedicated allocation. Using [`MemoryAllocatePreference::NeverAllocate`], a dedicated allocation
/// is never created, even if the allocation is larger than the block size or a dedicated
/// allocation is required. In such a case an error is returned instead. Using
/// [`MemoryAllocatePreference::AlwaysAllocate`], a dedicated allocation is always created.
///
/// In all other cases, `DeviceMemory` is only allocated if a pool runs out of memory and needs
/// another block. No `DeviceMemory` is allocated when the allocator is created, the blocks are
/// only allocated once they are needed.
///
/// # Locking behavior
///
/// The allocator never needs to lock while suballocating unless `S` needs to lock. The only time
/// when a pool must be locked is when a new `DeviceMemory` block is allocated for the pool. This
/// means that the allocator is suited to both locking and lock-free (sub)allocation algorithms.
///
/// [memory allocator]: MemoryAllocator
/// [suballocate]: Suballocator
/// [the `MemoryAllocator` implementation]: Self#impl-MemoryAllocator-for-GenericMemoryAllocator<S>
#[derive(Debug)]
pub struct GenericMemoryAllocator<S: Suballocator> {
    device: Arc<Device>,
    // Each memory type has a pool of `DeviceMemory` blocks.
    pools: ArrayVec<Pool<S>, MAX_MEMORY_TYPES>,
    // Each memory heap has its own block size.
    block_sizes: ArrayVec<DeviceSize, MAX_MEMORY_HEAPS>,
    allocation_type: AllocationType,
    dedicated_allocation: bool,
    export_handle_types: ArrayVec<ExternalMemoryHandleTypes, MAX_MEMORY_TYPES>,
    flags: MemoryAllocateFlags,
    // Global mask of memory types.
    memory_type_bits: u32,
    // How many `DeviceMemory` allocations should be allowed before restricting them.
    max_allocations: u32,
}

#[derive(Debug)]
struct Pool<S> {
    blocks: RwLock<Vec<S>>,
    // This is cached here for faster access, so we don't need to hop through 3 pointers.
    memory_type: ash::vk::MemoryType,
}

impl<S: Suballocator> GenericMemoryAllocator<S> {
    // This is a false-positive, we only use this const for static initialization.
    #[allow(clippy::declare_interior_mutable_const)]
    const EMPTY_POOL: Pool<S> = Pool {
        blocks: RwLock::new(Vec::new()),
        memory_type: ash::vk::MemoryType {
            property_flags: ash::vk::MemoryPropertyFlags::empty(),
            heap_index: 0,
        },
    };

    /// Creates a new `GenericMemoryAllocator<S>` using the provided suballocator `S` for
    /// suballocation of [`DeviceMemory`] blocks.
    ///
    /// # Panics
    ///
    /// - Panics if `create_info.block_sizes` is not sorted by threshold.
    /// - Panics if `create_info.block_sizes` contains duplicate thresholds.
    /// - Panics if `create_info.block_sizes` does not contain a baseline threshold of `0`.
    /// - Panics if the block size for a heap exceeds the size of the heap.
    pub fn new(
        device: Arc<Device>,
        create_info: GenericMemoryAllocatorCreateInfo<'_, '_>,
    ) -> Result<Self, GenericMemoryAllocatorCreationError> {
        Self::validate_new(&device, &create_info)?;

        Ok(unsafe { Self::new_unchecked(device, create_info) })
    }

    fn validate_new(
        device: &Device,
        create_info: &GenericMemoryAllocatorCreateInfo<'_, '_>,
    ) -> Result<(), GenericMemoryAllocatorCreationError> {
        let &GenericMemoryAllocatorCreateInfo {
            block_sizes,
            allocation_type: _,
            dedicated_allocation: _,
            export_handle_types,
            device_address: _,
            _ne: _,
        } = create_info;

        assert!(
            block_sizes.windows(2).all(|win| win[0].0 < win[1].0),
            "`create_info.block_sizes` must be sorted by threshold without duplicates",
        );
        assert!(
            matches!(block_sizes.first(), Some((0, _))),
            "`create_info.block_sizes` must contain a baseline threshold `0`",
        );

        if !export_handle_types.is_empty() {
            if !(device.api_version() >= Version::V1_1
                && device.enabled_extensions().khr_external_memory)
            {
                return Err(GenericMemoryAllocatorCreationError::RequirementNotMet {
                    required_for: "`create_info.export_handle_types` was not empty",
                    requires_one_of: RequiresOneOf {
                        api_version: Some(Version::V1_1),
                        device_extensions: &["khr_external_memory"],
                        ..Default::default()
                    },
                });
            }

            assert!(
                export_handle_types.len()
                    == device
                        .physical_device()
                        .memory_properties()
                        .memory_types
                        .len(),
                "`create_info.export_handle_types` must contain as many elements as the number of \
                memory types if not empty",
            );

            for export_handle_types in export_handle_types {
                // VUID-VkExportMemoryAllocateInfo-handleTypes-parameter
                export_handle_types.validate_device(device)?;
            }
        }

        Ok(())
    }

    #[cfg_attr(not(feature = "document_unchecked"), doc(hidden))]
    pub unsafe fn new_unchecked(
        device: Arc<Device>,
        create_info: GenericMemoryAllocatorCreateInfo<'_, '_>,
    ) -> Self {
        let GenericMemoryAllocatorCreateInfo {
            block_sizes,
            allocation_type,
            dedicated_allocation,
            export_handle_types,
            mut device_address,
            _ne: _,
        } = create_info;

        let MemoryProperties {
            memory_types,
            memory_heaps,
        } = device.physical_device().memory_properties();

        let mut pools = ArrayVec::new(memory_types.len(), [Self::EMPTY_POOL; MAX_MEMORY_TYPES]);
        for (i, memory_type) in memory_types.iter().enumerate() {
            pools[i].memory_type = ash::vk::MemoryType {
                property_flags: memory_type.property_flags.into(),
                heap_index: memory_type.heap_index,
            };
        }

        let block_sizes = {
            let mut sizes = ArrayVec::new(memory_heaps.len(), [0; MAX_MEMORY_HEAPS]);
            for (i, memory_heap) in memory_heaps.iter().enumerate() {
                let idx = match block_sizes.binary_search_by_key(&memory_heap.size, |&(t, _)| t) {
                    Ok(idx) => idx,
                    Err(idx) => idx.saturating_sub(1),
                };
                sizes[i] = block_sizes[idx].1;

                // VUID-vkAllocateMemory-pAllocateInfo-01713
                assert!(sizes[i] <= memory_heap.size);
            }

            sizes
        };

        let export_handle_types = {
            let mut types = ArrayVec::new(
                export_handle_types.len(),
                [ExternalMemoryHandleTypes::empty(); MAX_MEMORY_TYPES],
            );
            types.copy_from_slice(export_handle_types);

            types
        };

        // VUID-VkMemoryAllocateInfo-flags-03331
        device_address &= device.enabled_features().buffer_device_address
            && !device.enabled_extensions().ext_buffer_device_address;
        // Providers of `VkMemoryAllocateFlags`
        device_address &=
            device.api_version() >= Version::V1_1 || device.enabled_extensions().khr_device_group;

        let mut memory_type_bits = u32::MAX;
        for (index, MemoryType { property_flags, .. }) in memory_types.iter().enumerate() {
            if property_flags.lazily_allocated
                || property_flags.protected
                || property_flags.device_coherent
                || property_flags.device_uncached
                || property_flags.rdma_capable
            {
                // VUID-VkMemoryAllocateInfo-memoryTypeIndex-01872
                // VUID-vkAllocateMemory-deviceCoherentMemory-02790
                // Lazily allocated memory would just cause problems for suballocation in general.
                memory_type_bits &= !(1 << index);
            }
        }

        let max_memory_allocation_count = device
            .physical_device()
            .properties()
            .max_memory_allocation_count;
        let max_allocations = max_memory_allocation_count / 4 * 3;

        GenericMemoryAllocator {
            device,
            pools,
            block_sizes,
            allocation_type,
            dedicated_allocation,
            export_handle_types,
            flags: MemoryAllocateFlags {
                device_address,
                ..Default::default()
            },
            memory_type_bits,
            max_allocations,
        }
    }

    fn validate_allocate_from_type(
        &self,
        memory_type_index: u32,
        create_info: &SuballocationCreateInfo,
    ) {
        let memory_type = &self.pools[memory_type_index as usize].memory_type;
        // VUID-VkMemoryAllocateInfo-memoryTypeIndex-01872
        assert!(
            memory_type
                .property_flags
                .contains(ash::vk::MemoryPropertyFlags::PROTECTED)
                && !self.device.enabled_features().protected_memory,
            "attempted to allocate from a protected memory type without the `protected_memory` \
            feature being enabled on the device",
        );

        // VUID-vkAllocateMemory-deviceCoherentMemory-02790
        assert!(
            memory_type
                .property_flags
                .contains(ash::vk::MemoryPropertyFlags::DEVICE_COHERENT_AMD)
                && !self.device.enabled_features().device_coherent_memory,
            "attempted to allocate memory from a device-coherent memory type without the \
            `device_coherent_memory` feature being enabled on the device",
        );

        create_info.validate();
    }

    fn validate_allocate(&self, create_info: &AllocationCreateInfo<'_>) {
        let &AllocationCreateInfo {
            requirements,
            allocation_type: _,
            usage: _,
            allocate_preference: _,
            dedicated_allocation,
            _ne: _,
        } = create_info;

        SuballocationCreateInfo::from(create_info.clone()).validate();

        assert!(requirements.memory_type_bits != 0);
        assert!(requirements.memory_type_bits < 1 << self.pools.len());

        if let Some(dedicated_allocation) = dedicated_allocation {
            match dedicated_allocation {
                DedicatedAllocation::Buffer(buffer) => {
                    // VUID-VkMemoryDedicatedAllocateInfo-commonparent
                    assert_eq!(&self.device, buffer.device());

                    let required_size = buffer.memory_requirements().size;

                    // VUID-VkMemoryDedicatedAllocateInfo-buffer-02965
                    assert!(requirements.size != required_size);
                }
                DedicatedAllocation::Image(image) => {
                    // VUID-VkMemoryDedicatedAllocateInfo-commonparent
                    assert_eq!(&self.device, image.device());

                    let required_size = image.memory_requirements()[0].size;

                    // VUID-VkMemoryDedicatedAllocateInfo-image-02964
                    assert!(requirements.size != required_size);
                }
            }
        }

        // VUID-VkMemoryAllocateInfo-pNext-00639
        // VUID-VkExportMemoryAllocateInfo-handleTypes-00656
        // Can't validate, must be ensured by user
    }
}

unsafe impl<S: Suballocator> MemoryAllocator for GenericMemoryAllocator<S> {
    fn find_memory_type_index(
        &self,
        memory_type_bits: u32,
        filter: MemoryTypeFilter,
    ) -> Option<u32> {
        let required_flags = filter.required_flags.into();
        let preferred_flags = filter.preferred_flags.into();
        let not_preferred_flags = filter.not_preferred_flags.into();

        self.pools
            .iter()
            .map(|pool| pool.memory_type.property_flags)
            .enumerate()
            // Filter out memory types which are supported by the memory type bits and have the
            // required flags set.
            .filter(|&(index, flags)| {
                memory_type_bits & (1 << index) != 0 && flags & required_flags == required_flags
            })
            // Rank memory types with more of the preferred flags higher, and ones with more of the
            // not preferred flags lower.
            .min_by_key(|&(_, flags)| {
                (!flags & preferred_flags).as_raw().count_ones()
                    + (flags & not_preferred_flags).as_raw().count_ones()
            })
            .map(|(index, _)| index as u32)
    }

    /// Allocates memory from a specific memory type.
    ///
    /// # Panics
    ///
    /// - Panics if `memory_type_index` is not less than the number of available memory types.
    /// - Panics if `memory_type_index` refers to a memory type which has the [`protected`] flag set
    ///   and the [`protected_memory`] feature is not enabled on the device.
    /// - Panics if `memory_type_index` refers to a memory type which has the [`device_coherent`]
    ///   flag set and the [`device_coherent_memory`] feature is not enabled on the device.
    /// - Panics if `create_info.size` is zero.
    /// - Panics if `create_info.alignment` is zero.
    /// - Panics if `create_info.alignment` is not a power of two.
    ///
    /// # Errors
    ///
    /// - Returns an error if allocating a new block is required and failed. This can be one of the
    ///   OOM errors or [`TooManyObjects`].
    /// - Returns [`BlockSizeExceeded`] if `create_info.size` is greater than the block size
    ///   corresponding to the heap that the memory type corresponding to `memory_type_index`
    ///   resides in.
    /// - Returns [`SuballocatorBlockSizeExceeded`] if `S` is `PoolAllocator<BLOCK_SIZE>` and
    ///   `create_info.size` is greater than `BLOCK_SIZE`.
    ///
    /// [`protected`]: MemoryPropertyFlags::protected
    /// [`protected_memory`]: crate::device::Features::protected_memory
    /// [`device_coherent`]: MemoryPropertyFlags::device_coherent
    /// [`device_coherent_memory`]: crate::device::Features::device_coherent_memory
    /// [`TooManyObjects`]: VulkanError::TooManyObjects
    /// [`BlockSizeExceeded`]: AllocationCreationError::BlockSizeExceeded
    /// [`SuballocatorBlockSizeExceeded`]: AllocationCreationError::SuballocatorBlockSizeExceeded
    fn allocate_from_type(
        &self,
        memory_type_index: u32,
        create_info: SuballocationCreateInfo,
    ) -> Result<MemoryAlloc, AllocationCreationError> {
        self.validate_allocate_from_type(memory_type_index, &create_info);

        if self.pools[memory_type_index as usize]
            .memory_type
            .property_flags
            .contains(ash::vk::MemoryPropertyFlags::LAZILY_ALLOCATED)
        {
            return unsafe {
                self.allocate_dedicated_unchecked(
                    memory_type_index,
                    create_info.size,
                    None,
                    if !self.export_handle_types.is_empty() {
                        self.export_handle_types[memory_type_index as usize]
                    } else {
                        ExternalMemoryHandleTypes::empty()
                    },
                )
            };
        }

        unsafe { self.allocate_from_type_unchecked(memory_type_index, create_info, false) }
    }

    unsafe fn allocate_from_type_unchecked(
        &self,
        memory_type_index: u32,
        create_info: SuballocationCreateInfo,
        never_allocate: bool,
    ) -> Result<MemoryAlloc, AllocationCreationError> {
        let SuballocationCreateInfo {
            size,
            alignment: _,
            allocation_type: _,
            _ne: _,
        } = create_info;

        let pool = &self.pools[memory_type_index as usize];
        let block_size = self.block_sizes[pool.memory_type.heap_index as usize];

        if size > block_size {
            return Err(AllocationCreationError::BlockSizeExceeded);
        }

        let mut blocks = if S::IS_BLOCKING {
            // If the allocation algorithm needs to block, then there's no point in trying to avoid
            // locks here either. In that case the best strategy is to take full advantage of it by
            // always taking an exclusive lock, which lets us sort the blocks by free size. If you
            // as a user want to avoid locks, simply don't share the allocator between threads. You
            // can create as many allocators as you wish, but keep in mind that that will waste a
            // huge amount of memory unless you configure your block sizes properly!

            let mut blocks = pool.blocks.write();
            blocks.sort_by_key(Suballocator::free_size);
            let (Ok(idx) | Err(idx)) = blocks.binary_search_by_key(&size, Suballocator::free_size);
            for block in &blocks[idx..] {
                match block.allocate_unchecked(create_info.clone()) {
                    Ok(alloc) => return Ok(alloc),
                    Err(SuballocationCreationError::BlockSizeExceeded) => {
                        return Err(AllocationCreationError::SuballocatorBlockSizeExceeded);
                    }
                    Err(_) => {}
                }
            }

            blocks
        } else {
            // If the allocation algorithm is lock-free, then we should avoid taking an exclusive
            // lock unless it is absolutely neccessary (meaning, only when allocating a new
            // `DeviceMemory` block and inserting it into a pool). This has the disadvantage that
            // traversing the pool is O(n), which is not a problem since the number of blocks is
            // expected to be small. If there are more than 10 blocks in a pool then that's a
            // configuration error. Also, sorting the blocks before each allocation would be less
            // efficient because to get the free size of the `PoolAllocator` and `BumpAllocator`
            // has the same performance as trying to allocate.

            let blocks = pool.blocks.read();
            // Search in reverse order because we always append new blocks at the end.
            for block in blocks.iter().rev() {
                match block.allocate_unchecked(create_info.clone()) {
                    Ok(alloc) => return Ok(alloc),
                    // This can happen when using the `PoolAllocator<BLOCK_SIZE>` if the allocation
                    // size is greater than `BLOCK_SIZE`.
                    Err(SuballocationCreationError::BlockSizeExceeded) => {
                        return Err(AllocationCreationError::SuballocatorBlockSizeExceeded);
                    }
                    Err(_) => {}
                }
            }

            let len = blocks.len();
            drop(blocks);
            let blocks = pool.blocks.write();
            if blocks.len() > len {
                // Another thread beat us to it and inserted a fresh block, try to allocate from it.
                match blocks[len].allocate_unchecked(create_info.clone()) {
                    Ok(alloc) => return Ok(alloc),
                    // This can happen if this is the first block that was inserted and when using
                    // the `PoolAllocator<BLOCK_SIZE>` if the allocation size is greater than
                    // `BLOCK_SIZE`.
                    Err(SuballocationCreationError::BlockSizeExceeded) => {
                        return Err(AllocationCreationError::SuballocatorBlockSizeExceeded);
                    }
                    Err(_) => {}
                }
            }

            blocks
        };

        // For bump allocators, first do a garbage sweep and try to allocate again.
        if S::NEEDS_CLEANUP {
            blocks.iter_mut().for_each(Suballocator::cleanup);
            blocks.sort_unstable_by_key(Suballocator::free_size);

            if let Some(block) = blocks.last() {
                if let Ok(alloc) = block.allocate_unchecked(create_info.clone()) {
                    return Ok(alloc);
                }
            }
        }

        if never_allocate {
            return Err(AllocationCreationError::OutOfPoolMemory);
        }

        // The pool doesn't have enough real estate, so we need a new block.
        let block = {
            let export_handle_types = if !self.export_handle_types.is_empty() {
                self.export_handle_types[memory_type_index as usize]
            } else {
                ExternalMemoryHandleTypes::empty()
            };
            let mut i = 0;

            loop {
                let allocate_info = MemoryAllocateInfo {
                    allocation_size: block_size >> i,
                    memory_type_index,
                    export_handle_types,
                    dedicated_allocation: None,
                    flags: self.flags,
                    ..Default::default()
                };
                match DeviceMemory::allocate_unchecked(self.device.clone(), allocate_info, None) {
                    Ok(device_memory) => {
                        break S::new(MemoryAlloc::new(device_memory)?);
                    }
                    // Retry up to 3 times, halving the allocation size each time.
                    Err(VulkanError::OutOfHostMemory | VulkanError::OutOfDeviceMemory) if i < 3 => {
                        i += 1;
                    }
                    Err(err) => return Err(err.into()),
                }
            }
        };

        blocks.push(block);
        let block = blocks.last().unwrap();

        match block.allocate_unchecked(create_info) {
            Ok(alloc) => Ok(alloc),
            // This can happen if the block ended up smaller than advertised because there wasn't
            // enough memory.
            Err(SuballocationCreationError::OutOfRegionMemory) => Err(
                AllocationCreationError::VulkanError(VulkanError::OutOfDeviceMemory),
            ),
            // This can not happen as the block is fresher than Febreze and we're still holding an
            // exclusive lock.
            Err(SuballocationCreationError::FragmentedRegion) => unreachable!(),
            // This can happen if this is the first block that was inserted and when using the
            // `PoolAllocator<BLOCK_SIZE>` if the allocation size is greater than `BLOCK_SIZE`.
            Err(SuballocationCreationError::BlockSizeExceeded) => {
                Err(AllocationCreationError::SuballocatorBlockSizeExceeded)
            }
        }
    }

    /// Allocates memory according to requirements.
    ///
    /// # Panics
    ///
    /// - Panics if `create_info.requirements.size` is zero.
    /// - Panics if `create_info.requirements.alignment` is zero.
    /// - Panics if `create_info.requirements.alignment` is not a power of two.
    /// - Panics if `create_info.requirements.memory_type_bits` is zero.
    /// - Panics if `create_info.requirements.memory_type_bits` is not less than 2<sup>*n*</sup>
    ///   where *n* is the number of available memory types.
    /// - Panics if `create_info.dedicated_allocation` is `Some` and
    ///   `create_info.requirements.size` doesn't match the memory requirements of the resource.
    /// - Panics if finding a suitable memory type failed. This only happens if the
    ///   `create_info.requirements` correspond to those of an optimal image but
    ///   `create_info.usage` is not [`MemoryUsage::GpuOnly`].
    ///
    /// # Errors
    ///
    /// - Returns an error if allocating a new block is required and failed. This can be one of the
    ///   OOM errors or [`TooManyObjects`].
    /// - Returns [`OutOfPoolMemory`] if `create_info.allocate_preference` is
    ///   [`MemoryAllocatePreference::NeverAllocate`] and none of the pools of suitable memory
    ///   types have enough free space.
    /// - Returns [`DedicatedAllocationRequired`] if `create_info.allocate_preference` is
    ///   [`MemoryAllocatePreference::NeverAllocate`] and
    ///   `create_info.requirements.requires_dedicated_allocation` is `true`.
    /// - Returns [`BlockSizeExceeded`] if `create_info.allocate_preference` is
    ///   [`MemoryAllocatePreference::NeverAllocate`] and `create_info.requirements.size` is greater
    ///   than the block size for all heaps of suitable memory types.
    /// - Returns [`SuballocatorBlockSizeExceeded`] if `S` is `PoolAllocator<BLOCK_SIZE>` and
    ///   `create_info.size` is greater than `BLOCK_SIZE` and a dedicated allocation was not
    ///   created.
    ///
    /// [`device_local`]: MemoryPropertyFlags::device_local
    /// [`host_visible`]: MemoryPropertyFlags::host_visible
    /// [`TooManyObjects`]: VulkanError::TooManyObjects
    /// [`SuballocatorBlockSizeExceeded`]: AllocationCreationError::SuballocatorBlockSizeExceeded
    /// [`OutOfPoolMemory`]: AllocationCreationError::OutOfPoolMemory
    /// [`DedicatedAllocationRequired`]: AllocationCreationError::DedicatedAllocationRequired
    /// [`BlockSizeExceeded`]: AllocationCreationError::BlockSizeExceeded
    fn allocate(
        &self,
        create_info: AllocationCreateInfo<'_>,
    ) -> Result<MemoryAlloc, AllocationCreationError> {
        self.validate_allocate(&create_info);

        unsafe { self.allocate_unchecked(create_info) }
    }

    unsafe fn allocate_unchecked(
        &self,
        create_info: AllocationCreateInfo<'_>,
    ) -> Result<MemoryAlloc, AllocationCreationError> {
        let AllocationCreateInfo {
            requirements:
                MemoryRequirements {
                    size,
                    alignment: _,
                    mut memory_type_bits,
                    mut prefers_dedicated_allocation,
                    requires_dedicated_allocation,
                },
            allocation_type: _,
            usage,
            allocate_preference,
            mut dedicated_allocation,
            _ne: _,
        } = create_info;

        let create_info = SuballocationCreateInfo::from(create_info);

        memory_type_bits &= self.memory_type_bits;

        let filter = usage.into();

        let mut memory_type_index = self
            .find_memory_type_index(memory_type_bits, filter)
            .expect("couldn't find a suitable memory type");
        if !self.dedicated_allocation {
            dedicated_allocation = None;
        }
        let export_handle_types = if self.export_handle_types.is_empty() {
            ExternalMemoryHandleTypes::empty()
        } else {
            self.export_handle_types[memory_type_index as usize]
        };

        loop {
            let memory_type = self.pools[memory_type_index as usize].memory_type;
            let block_size = self.block_sizes[memory_type.heap_index as usize];

            let res = match allocate_preference {
                MemoryAllocatePreference::Unknown => {
                    if requires_dedicated_allocation {
                        self.allocate_dedicated_unchecked(
                            memory_type_index,
                            size,
                            dedicated_allocation,
                            export_handle_types,
                        )
                    } else {
                        if size > block_size / 2 {
                            prefers_dedicated_allocation = true;
                        }
                        if self.device.allocation_count() > self.max_allocations
                            && size <= block_size
                        {
                            prefers_dedicated_allocation = false;
                        }

                        if prefers_dedicated_allocation {
                            self.allocate_dedicated_unchecked(
                                memory_type_index,
                                size,
                                dedicated_allocation,
                                export_handle_types,
                            )
                            // Fall back to suballocation.
                            .or_else(|err| {
                                if size <= block_size {
                                    self.allocate_from_type_unchecked(
                                        memory_type_index,
                                        create_info.clone(),
                                        true, // A dedicated allocation already failed.
                                    )
                                    .map_err(|_| err)
                                } else {
                                    Err(err)
                                }
                            })
                        } else {
                            self.allocate_from_type_unchecked(
                                memory_type_index,
                                create_info.clone(),
                                false,
                            )
                            // Fall back to dedicated allocation. It is possible that the 1/8 block
                            // size tried was greater than the allocation size, so there's hope.
                            .or_else(|_| {
                                self.allocate_dedicated_unchecked(
                                    memory_type_index,
                                    size,
                                    dedicated_allocation,
                                    export_handle_types,
                                )
                            })
                        }
                    }
                }
                MemoryAllocatePreference::NeverAllocate => {
                    if requires_dedicated_allocation {
                        return Err(AllocationCreationError::DedicatedAllocationRequired);
                    }

                    self.allocate_from_type_unchecked(memory_type_index, create_info.clone(), true)
                }
                MemoryAllocatePreference::AlwaysAllocate => self.allocate_dedicated_unchecked(
                    memory_type_index,
                    size,
                    dedicated_allocation,
                    export_handle_types,
                ),
            };

            match res {
                Ok(alloc) => return Ok(alloc),
                // This is not recoverable.
                Err(AllocationCreationError::SuballocatorBlockSizeExceeded) => {
                    return Err(AllocationCreationError::SuballocatorBlockSizeExceeded);
                }
                // Try a different memory type.
                Err(err) => {
                    memory_type_bits &= !(1 << memory_type_index);
                    memory_type_index = self
                        .find_memory_type_index(memory_type_bits, filter)
                        .ok_or(err)?;
                }
            }
        }
    }

    unsafe fn allocate_dedicated_unchecked(
        &self,
        memory_type_index: u32,
        allocation_size: DeviceSize,
        mut dedicated_allocation: Option<DedicatedAllocation<'_>>,
        export_handle_types: ExternalMemoryHandleTypes,
    ) -> Result<MemoryAlloc, AllocationCreationError> {
        // Providers of `VkMemoryDedicatedAllocateInfo`
        if !(self.device.api_version() >= Version::V1_1
            || self.device.enabled_extensions().khr_dedicated_allocation)
        {
            dedicated_allocation = None;
        }

        let allocate_info = MemoryAllocateInfo {
            allocation_size,
            memory_type_index,
            dedicated_allocation,
            export_handle_types,
            flags: self.flags,
            ..Default::default()
        };
        let mut alloc = MemoryAlloc::new(
            DeviceMemory::allocate_unchecked(self.device.clone(), allocate_info, None)
                .map_err(AllocationCreationError::from)?,
        )?;
        alloc.set_allocation_type(self.allocation_type);

        Ok(alloc)
    }
}

unsafe impl<S: Suballocator> MemoryAllocator for Arc<GenericMemoryAllocator<S>> {
    fn find_memory_type_index(
        &self,
        memory_type_bits: u32,
        filter: MemoryTypeFilter,
    ) -> Option<u32> {
        (**self).find_memory_type_index(memory_type_bits, filter)
    }

    fn allocate_from_type(
        &self,
        memory_type_index: u32,
        create_info: SuballocationCreateInfo,
    ) -> Result<MemoryAlloc, AllocationCreationError> {
        (**self).allocate_from_type(memory_type_index, create_info)
    }

    unsafe fn allocate_from_type_unchecked(
        &self,
        memory_type_index: u32,
        create_info: SuballocationCreateInfo,
        never_allocate: bool,
    ) -> Result<MemoryAlloc, AllocationCreationError> {
        (**self).allocate_from_type_unchecked(memory_type_index, create_info, never_allocate)
    }

    fn allocate(
        &self,
        create_info: AllocationCreateInfo<'_>,
    ) -> Result<MemoryAlloc, AllocationCreationError> {
        (**self).allocate(create_info)
    }

    unsafe fn allocate_unchecked(
        &self,
        create_info: AllocationCreateInfo<'_>,
    ) -> Result<MemoryAlloc, AllocationCreationError> {
        (**self).allocate_unchecked(create_info)
    }

    unsafe fn allocate_dedicated_unchecked(
        &self,
        memory_type_index: u32,
        allocation_size: DeviceSize,
        dedicated_allocation: Option<DedicatedAllocation<'_>>,
        export_handle_types: ExternalMemoryHandleTypes,
    ) -> Result<MemoryAlloc, AllocationCreationError> {
        (**self).allocate_dedicated_unchecked(
            memory_type_index,
            allocation_size,
            dedicated_allocation,
            export_handle_types,
        )
    }
}

unsafe impl<S: Suballocator> DeviceOwned for GenericMemoryAllocator<S> {
    fn device(&self) -> &Arc<Device> {
        &self.device
    }
}

/// Parameters to create a new [`GenericMemoryAllocator`].
#[derive(Clone, Debug)]
pub struct GenericMemoryAllocatorCreateInfo<'b, 'e> {
    /// Lets you configure the block sizes for various heap size classes.
    ///
    /// Each entry is a pair of the threshold for the heap size and the block size that should be
    /// used for that heap. Must be sorted by threshold and all thresholds must be unique. Must
    /// contain a baseline threshold of 0.
    ///
    /// The allocator keeps a pool of [`DeviceMemory`] blocks for each memory type, so each memory
    /// type that resides in a heap whose size crosses one of the thresholds will use the
    /// corresponding block size. If multiple thresholds apply to a given heap, the block size
    /// corresponding to the largest threshold is chosen.
    ///
    /// The block size is going to be the maximum size of a `DeviceMemory` block that is tried. If
    /// allocating a block with the size fails, the allocator tries 1/2, 1/4 and 1/8 of the block
    /// size in that order until one succeeds, else a dedicated allocation is attempted for the
    /// allocation. If an allocation is created with a size greater than half the block size it is
    /// always made a dedicated allocation. All of this doesn't apply when using
    /// [`MemoryAllocatePreference::NeverAllocate`] however.
    ///
    /// The default value is `&[]`, which must be overridden.
    pub block_sizes: &'b [(Threshold, BlockSize)],

    /// The allocation type that should be used for root allocations.
    ///
    /// You only need to worry about this if you're using [`PoolAllocator`] as the suballocator, as
    /// all suballocations that the pool allocator makes inherit their allocation type from the
    /// parent allocation. For the [`FreeListAllocator`] and the [`BuddyAllocator`] this must be
    /// [`AllocationType::Unknown`] otherwise you will get panics. It does not matter what this is
    /// when using the [`BumpAllocator`].
    ///
    /// The default value is [`AllocationType::Unknown`].
    pub allocation_type: AllocationType,

    /// Whether the allocator should use the dedicated allocation APIs.
    ///
    /// This means that when the allocator decides that an allocation should not be suballocated,
    /// but rather have its own block of [`DeviceMemory`], that that allocation will be made a
    /// dedicated allocation. Otherwise they are still made free-standing ([root]) allocations,
    /// just not [dedicated] ones.
    ///
    /// Dedicated allocations are an optimization which may result in better performance, so there
    /// really is no reason to disable this option, unless the restrictions that they bring with
    /// them are a problem. Namely, a dedicated allocation must only be used for the resource it
    /// was created for. Meaning that [reusing the memory] for something else is not possible,
    /// [suballocating it] is not possible, and [aliasing it] is also not possible.
    ///
    /// This option is silently ignored (treated as `false`) if the device API version is below 1.1
    /// and the [`khr_dedicated_allocation`] extension is not enabled on the device.
    ///
    /// The default value is `true`.
    ///
    /// [root]: MemoryAlloc::is_root
    /// [dedicated]: MemoryAlloc::is_dedicated
    /// [reusing the memory]: MemoryAlloc::try_unwrap
    /// [suballocating it]: Suballocator
    /// [aliasing it]: MemoryAlloc::alias
    /// [`khr_dedicated_allocation`]: crate::device::DeviceExtensions::khr_dedicated_allocation
    pub dedicated_allocation: bool,

    /// Lets you configure the external memory handle types that the [`DeviceMemory`] blocks will
    /// be allocated with.
    ///
    /// Must be either empty or contain one element for each memory type. When `DeviceMemory` is
    /// allocated, the external handle types corresponding to the memory type index are looked up
    /// here and used for the allocation.
    ///
    /// The default value is `&[]`.
    pub export_handle_types: &'e [ExternalMemoryHandleTypes],

    /// Whether the allocator should allocate the [`DeviceMemory`] blocks with the
    /// [`device_address`] flag set.
    ///
    /// This is required if you want to allocate memory for buffers that have the
    /// [`shader_device_address`] usage set. For this option too, there is no reason to disable it.
    ///
    /// This option is silently ignored (treated as `false`) if the [`buffer_device_address`]
    /// feature is not enabled on the device or if the [`ext_buffer_device_address`] extension is
    /// enabled on the device. It is also ignored if the device API version is below 1.1 and the
    /// [`khr_device_group`] extension is not enabled on the device.
    ///
    /// The default value is `true`.
    ///
    /// [`device_address`]: MemoryAllocateFlags::device_address
    /// [`shader_device_address`]: crate::buffer::BufferUsage::shader_device_address
    /// [`buffer_device_address`]: crate::device::Features::buffer_device_address
    /// [`ext_buffer_device_address`]: crate::device::DeviceExtensions::ext_buffer_device_address
    /// [`khr_device_group`]: crate::device::DeviceExtensions::khr_device_group
    pub device_address: bool,

    pub _ne: crate::NonExhaustive,
}

pub type Threshold = DeviceSize;

pub type BlockSize = DeviceSize;

impl Default for GenericMemoryAllocatorCreateInfo<'_, '_> {
    #[inline]
    fn default() -> Self {
        GenericMemoryAllocatorCreateInfo {
            block_sizes: &[],
            allocation_type: AllocationType::Unknown,
            dedicated_allocation: true,
            export_handle_types: &[],
            device_address: true,
            _ne: crate::NonExhaustive(()),
        }
    }
}

/// Error that can be returned when creating a [`GenericMemoryAllocator`].
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum GenericMemoryAllocatorCreationError {
    RequirementNotMet {
        required_for: &'static str,
        requires_one_of: RequiresOneOf,
    },
}

impl Error for GenericMemoryAllocatorCreationError {}

impl Display for GenericMemoryAllocatorCreationError {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), FmtError> {
        match self {
            Self::RequirementNotMet {
                required_for,
                requires_one_of,
            } => write!(
                f,
                "a requirement was not met for: {}; requires one of: {}",
                required_for, requires_one_of,
            ),
        }
    }
}

impl From<RequirementNotMet> for GenericMemoryAllocatorCreationError {
    fn from(err: RequirementNotMet) -> Self {
        Self::RequirementNotMet {
            required_for: err.required_for,
            requires_one_of: err.requires_one_of,
        }
    }
}

mod array_vec {
    use std::ops::{Deref, DerefMut};

    /// Minimal implementation of an `ArrayVec`. Useful when a `Vec` is needed but there is a known
    /// limit on the number of elements, so that it can occupy real estate on the stack.
    #[derive(Clone, Copy, Debug)]
    pub(super) struct ArrayVec<T, const N: usize> {
        len: usize,
        data: [T; N],
    }

    impl<T, const N: usize> ArrayVec<T, N> {
        pub fn new(len: usize, data: [T; N]) -> Self {
            assert!(len <= N);

            ArrayVec { len, data }
        }
    }

    impl<T, const N: usize> Deref for ArrayVec<T, N> {
        type Target = [T];

        fn deref(&self) -> &Self::Target {
            // SAFETY: `self.len <= N`.
            unsafe { self.data.get_unchecked(0..self.len) }
        }
    }

    impl<T, const N: usize> DerefMut for ArrayVec<T, N> {
        fn deref_mut(&mut self) -> &mut Self::Target {
            // SAFETY: `self.len <= N`.
            unsafe { self.data.get_unchecked_mut(0..self.len) }
        }
    }
}