# lib.rs - source
Source of the Rust file `/home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/buddy_system_allocator-0.6.0/src/lib.rs`.
Keywords: rust, rustlang, rust-lang

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    #![cfg_attr(feature = "const_fn", feature(const_mut_refs, const_fn_fn_ptr_basics))]
    #![no_std]

    #[cfg(test)]
    #[macro_use]
    extern crate std;

    #[cfg(feature = "use_spin")]
    extern crate spin;

    extern crate alloc;

    use core::alloc::{GlobalAlloc, Layout};
    use core::cmp::{max, min};
    use core::fmt;
    use core::mem::size_of;
    #[cfg(feature = "use_spin")]
    use core::ops::Deref;
    use core::ptr::NonNull;
    #[cfg(feature = "use_spin")]
    use spin::Mutex;

    mod frame;
    pub mod linked_list;
    #[cfg(test)]
    mod test;

    pub use frame::*;

    /// A heap that uses buddy system
    ///
    /// # Usage
    ///
    /// Create a heap and add a memory region to it:
    /// ```
    /// use buddy_system_allocator::*;
    /// # use core::mem::size_of;
    /// let mut heap = Heap::empty();
    /// # let space: [usize; 100] = [0; 100];
    /// # let begin: usize = space.as_ptr() as usize;
    /// # let end: usize = begin + 100 * size_of::<usize>();
    /// # let size: usize = 100 * size_of::<usize>();
    /// unsafe {
    ///     heap.init(begin, size);
    ///     // or
    ///     heap.add_to_heap(begin, end);
    /// }
    /// ```
    pub struct Heap {
        // buddy system with max order of 32
        free_list: [linked_list::LinkedList; 32],

        // statistics
        user: usize,
        allocated: usize,
        total: usize,
    }

    impl Heap {
        /// Create an empty heap
        pub const fn new() -> Self {
            Heap {
                free_list: [linked_list::LinkedList::new(); 32],
                user: 0,
                allocated: 0,
                total: 0,
            }
        }

        /// Create an empty heap
        pub const fn empty() -> Self {
            Self::new()
        }

        /// Add a range of memory [start, end) to the heap
        pub unsafe fn add_to_heap(&mut self, mut start: usize, mut end: usize) {
            // avoid unaligned access on some platforms
            start = (start + size_of::<usize>() - 1) & (!size_of::<usize>() + 1);
            end = end & (!size_of::<usize>() + 1);
            assert!(start <= end);

            let mut total = 0;
            let mut current_start = start;

            while current_start + size_of::<usize>() <= end {
                let lowbit = current_start & (!current_start + 1);
                let size = min(lowbit, prev_power_of_two(end - current_start));
                total += size;

                self.free_list[size.trailing_zeros() as usize].push(current_start as *mut usize);
                current_start += size;
            }

            self.total += total;
        }

        /// Add a range of memory [start, end) to the heap
        pub unsafe fn init(&mut self, start: usize, size: usize) {
            self.add_to_heap(start, start + size);
        }

        /// Alloc a range of memory from the heap satifying `layout` requirements
        pub fn alloc(&mut self, layout: Layout) -> Result<NonNull<u8>, ()> {
            let size = max(
                layout.size().next_power_of_two(),
                max(layout.align(), size_of::<usize>()),
            );
            let class = size.trailing_zeros() as usize;
            for i in class..self.free_list.len() {
                // Find the first non-empty size class
                if !self.free_list[i].is_empty() {
                    // Split buffers
                    for j in (class + 1..i + 1).rev() {
                        if let Some(block) = self.free_list[j].pop() {
                            unsafe {
                                self.free_list[j - 1]
                                    .push((block as usize + (1 << (j - 1))) as *mut usize);
                                self.free_list[j - 1].push(block);
                            }
                        } else {
                            return Err(());
                        }
                    }

                    let result = NonNull::new(
                        self.free_list[class]
                            .pop()
                            .expect("current block should have free space now")
                            as *mut u8,
                    );
                    if let Some(result) = result {
                        self.user += layout.size();
                        self.allocated += size;
                        return Ok(result);
                    } else {
                        return Err(());
                    }
                }
            }
            Err(())
        }

        /// Dealloc a range of memory from the heap
        pub fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
            let size = max(
                layout.size().next_power_of_two(),
                max(layout.align(), size_of::<usize>()),
            );
            let class = size.trailing_zeros() as usize;

            unsafe {
                // Put back into free list
                self.free_list[class].push(ptr.as_ptr() as *mut usize);

                // Merge free buddy lists
                let mut current_ptr = ptr.as_ptr() as usize;
                let mut current_class = class;
                while current_class < self.free_list.len() {
                    let buddy = current_ptr ^ (1 << current_class);
                    let mut flag = false;
                    for block in self.free_list[current_class].iter_mut() {
                        if block.value() as usize == buddy {
                            block.pop();
                            flag = true;
                            break;
                        }
                    }

                    // Free buddy found
                    if flag {
                        self.free_list[current_class].pop();
                        current_ptr = min(current_ptr, buddy);
                        current_class += 1;
                        self.free_list[current_class].push(current_ptr as *mut usize);
                    } else {
                        break;
                    }
                }
            }

            self.user -= layout.size();
            self.allocated -= size;
        }

        /// Return the number of bytes that user requests
        pub fn stats_alloc_user(&self) -> usize {
            self.user
        }

        /// Return the number of bytes that are actually allocated
        pub fn stats_alloc_actual(&self) -> usize {
            self.allocated
        }

        /// Return the total number of bytes in the heap
        pub fn stats_total_bytes(&self) -> usize {
            self.total
        }
    }

    impl fmt::Debug for Heap {
        fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
            fmt.debug_struct("Heap")
                .field("user", &self.user)
                .field("allocated", &self.allocated)
                .field("total", &self.total)
                .finish()
        }
    }

    /// A locked version of `Heap`
    ///
    /// # Usage
    ///
    /// Create a locked heap and add a memory region to it:
    /// ```
    /// use buddy_system_allocator::*;
    /// # use core::mem::size_of;
    /// let mut heap = LockedHeap::new();
    /// # let space: [usize; 100] = [0; 100];
    /// # let begin: usize = space.as_ptr() as usize;
    /// # let end: usize = begin + 100 * size_of::<usize>();
    /// # let size: usize = 100 * size_of::<usize>();
    /// unsafe {
    ///     heap.lock().init(begin, size);
    ///     // or
    ///     heap.lock().add_to_heap(begin, end);
    /// }
    /// ```
    #[cfg(feature = "use_spin")]
    pub struct LockedHeap(Mutex<Heap>);

    #[cfg(feature = "use_spin")]
    impl LockedHeap {
        /// Creates an empty heap
        pub const fn new() -> LockedHeap {
            LockedHeap(Mutex::new(Heap::new()))
        }

        /// Creates an empty heap
        pub const fn empty() -> LockedHeap {
            LockedHeap(Mutex::new(Heap::new()))
        }
    }

    #[cfg(feature = "use_spin")]
    impl Deref for LockedHeap {
        type Target = Mutex<Heap>;

        fn deref(&self) -> &Mutex<Heap> {
            &self.0
        }
    }

    #[cfg(feature = "use_spin")]
    unsafe impl GlobalAlloc for LockedHeap {
        unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
            self.0
                .lock()
                .alloc(layout)
                .ok()
                .map_or(0 as *mut u8, |allocation| allocation.as_ptr())
        }

        unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
            self.0.lock().dealloc(NonNull::new_unchecked(ptr), layout)
        }
    }

    /// A locked version of `Heap` with rescue before oom
    ///
    /// # Usage
    ///
    /// Create a locked heap:
    /// ```
    /// use buddy_system_allocator::*;
    /// let heap = LockedHeapWithRescue::new(|heap: &mut Heap| {});
    /// ```
    ///
    /// Before oom, the allocator will try to call rescue function and try for one more time.
    #[cfg(feature = "use_spin")]
    pub struct LockedHeapWithRescue {
        inner: Mutex<Heap>,
        rescue: fn(&mut Heap),
    }

    #[cfg(feature = "use_spin")]
    impl LockedHeapWithRescue {
        /// Creates an empty heap
        #[cfg(feature = "const_fn")]
        pub const fn new(rescue: fn(&mut Heap)) -> LockedHeapWithRescue {
            LockedHeapWithRescue {
                inner: Mutex::new(Heap::new()),
                rescue,
            }
        }

        /// Creates an empty heap
        #[cfg(not(feature = "const_fn"))]
        pub fn new(rescue: fn(&mut Heap)) -> LockedHeapWithRescue {
            LockedHeapWithRescue {
                inner: Mutex::new(Heap::new()),
                rescue,
            }
        }
    }

    #[cfg(feature = "use_spin")]
    impl Deref for LockedHeapWithRescue {
        type Target = Mutex<Heap>;

        fn deref(&self) -> &Mutex<Heap> {
            &self.inner
        }
    }

    #[cfg(feature = "use_spin")]
    unsafe impl GlobalAlloc for LockedHeapWithRescue {
        unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
            let mut inner = self.inner.lock();
            match inner.alloc(layout) {
                Ok(allocation) => allocation.as_ptr(),
                Err(_) => {
                    (self.rescue)(&mut inner);
                    inner
                        .alloc(layout)
                        .ok()
                        .map_or(0 as *mut u8, |allocation| allocation.as_ptr())
                }
            }
        }

        unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
            self.inner
                .lock()
                .dealloc(NonNull::new_unchecked(ptr), layout)
        }
    }

    pub(crate) fn prev_power_of_two(num: usize) -> usize {
        1 << (8 * (size_of::<usize>()) - num.leading_zeros() as usize - 1)
    }