1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155

use core::alloc::Layout;
use core::ptr::{NonNull, slice_from_raw_parts_mut};
use core::sync::atomic::{AtomicPtr, AtomicUsize, Ordering};
use bern_units::memory_size::{Byte, ExtByte};
use crate::alloc::allocator::{Allocator, AllocError};
use crate::log;

/// The strict memory allocator can allocate memory but never release.
pub struct Bump {
    /// Start of memory block.
    start: NonNull<u8>,
    /// End of memory block.
    end: NonNull<u8>,
    /// Current allocation pointer.
    current: AtomicPtr<u8>,
    /// Memory wasted due to padding.
    wastage: AtomicUsize,
}

impl Bump {
    ///
    /// # Safety
    /// `start` must be a valid address and the memory block must not exceed its
    /// intended range.
    pub const unsafe fn new(start: NonNull<u8>, end: NonNull<u8>) -> Self {
        Bump {
            start,
            end,
            current: AtomicPtr::new(start.as_ptr()),
            wastage: AtomicUsize::new(0),
        }
    }
}

impl Allocator for Bump {
    fn alloc(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        loop { // CAS loop
            let old = self.current.load(Ordering::Acquire);
            let padding = old.align_offset(layout.align());
            log::trace!(
                "Try to allocate {}B at 0x{:x}",
                layout.size(),
                old as usize + padding
            );

            if (self.capacity() - self.usage()) < ((layout.size() + padding) as u32).B() {
                return Err(AllocError::OutOfMemory);
            }

            // Note(unsafe): We checked the size requirements already
            unsafe {
                match self.current.compare_exchange(
                    old,
                    old.add(layout.size() + padding),
                    Ordering::SeqCst,
                    Ordering::Relaxed
                ) {
                    Ok(_) => {
                        let memory = slice_from_raw_parts_mut(old.add(padding), layout.size());
                        self.wastage.fetch_add(padding, Ordering::Relaxed);
                        return Ok(NonNull::new_unchecked(memory));
                    },
                    Err(_) => continue, // Allocation was interrupted, restart
                }
            }
        }
    }

    unsafe fn dealloc(&self, ptr: NonNull<u8>, layout: Layout) {
        log::warn!(
            "BumpAllocator cannot deallocate memory (0x{:x}, {}B). Ignoring call from .",
            ptr.as_ptr() as usize,
            layout.size()
        );
        self.wastage.fetch_add(layout.size(), Ordering::Relaxed);
    }

    fn capacity(&self) -> Byte {
        Byte((self.end.as_ptr() as usize - self.start.as_ptr() as usize) as u32)
    }

    fn usage(&self) -> Byte {
        Byte((self.current.load(Ordering::Relaxed) as usize -
            self.start.as_ptr() as usize) as u32)
    }
}

// Note(unsafe): We use atomic pointers.
unsafe impl Sync for Bump { }


#[cfg(all(test, not(target_os = "none")))]
mod tests {
    use core::mem::{align_of, size_of};
    use super::*;

    struct MyStruct {
        a: u32,
        b: u8,
    }

    #[test]
    fn alloc_and_dealloc() {
        // Manually align array to 32 bit by using `u32`.
        static mut BUFFER: [u32; 128/4] = [0; 128/4];

        let bump = unsafe { Bump::new(
            NonNull::new_unchecked(BUFFER.as_ptr() as *mut _),
            NonNull::new_unchecked(BUFFER.as_ptr().add(BUFFER.len()) as *mut _)
        )};
        assert_eq!(bump.capacity().0, 128);

        let layout = Layout::from_size_align(size_of::<MyStruct>(), align_of::<MyStruct>()).unwrap();
        let raw = bump.alloc(layout).unwrap();

        let memory = raw.cast::<MyStruct>();
        let s = unsafe { &mut *memory.as_ptr() };

        // Check that we can actually write to the variable.
        s.a = 42;
        s.b = 10;

        let usage = size_of::<MyStruct>() as u32;
        assert_eq!(bump.usage().0, (usage + bump.wastage.load(Ordering::Relaxed) as u32));
        let wastage = bump.wastage.load(Ordering::Relaxed);

        unsafe {
            bump.dealloc(raw.cast::<u8>(), layout);
        }
        // Memory can not be reused only wasted with the bump allocator.
        assert_eq!(bump.usage().0, usage);
        assert_eq!(bump.wastage.load(Ordering::Relaxed), wastage + size_of::<MyStruct>());
    }

    #[test]
    fn overflow() {
        static mut BUFFER: [u8; 128] = [0; 128];

        let bump = unsafe { Bump::new(
            NonNull::new_unchecked(BUFFER.as_ptr() as *mut _),
            NonNull::new_unchecked(BUFFER.as_ptr().add(BUFFER.len()) as *mut _)
        )};
        assert_eq!(bump.capacity().0, 128);

        let layout = Layout::from_size_align(16, 1).unwrap();
        for _ in 0..8 {
            let _dump = bump.alloc(layout).unwrap();
        }

        assert_eq!(bump.usage(), bump.capacity());

        let err = bump.alloc(layout).err().unwrap();
        assert_eq!(err, AllocError::OutOfMemory);
    }
}