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@notcancername
Created January 29, 2024 00:48
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A simple allocator wrapper with a free list, sort of, to reuse allocations.
// SPDX-License-Identifier: 0BSD
// Copyright (C) 2024 by cancername <notcancername@protonmail.com>
//
// Permission to use, copy, modify, and/or distribute this software for any purpose with or without
// fee is hereby granted.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
// SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
// NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
// OF THIS SOFTWARE.
const std = @import("std");
const mem = std.mem;
const heap = std.heap;
// TODO: This is lazy.
pub const FreeListAllocator = struct {
const Allocation = struct {
len: usize,
ptr: usize,
log2_align: u8,
};
const max_allocations = 16;
inner: mem.Allocator = heap.page_allocator,
allocations: std.BoundedArray(Allocation, max_allocations) = .{},
pub fn allocator(fla: *FreeListAllocator) mem.Allocator {
return .{
.ptr = @ptrCast(fla),
.vtable = &.{
.alloc = alloc,
.resize = resize,
.free = free,
},
};
}
pub fn deinit(fla: *FreeListAllocator) void {
for (fla.allocations.constSlice()) |allocation| {
fla.inner.rawFree(@as([*]u8, @ptrFromInt(allocation.ptr))[0..allocation.len], allocation.log2_align, 0);
}
}
fn alloc(ctx: *anyopaque, len: usize, log2_align: u8, ret_addr: usize) ?[*]u8 {
const state: *FreeListAllocator = @ptrCast(@alignCast(ctx));
for (state.allocations.constSlice(), 0..) |allocation, i| {
if (allocation.log2_align == log2_align) {
if(allocation.len == len) {
defer _ = state.allocations.swapRemove(i);
return @ptrFromInt(allocation.ptr);
} else if(allocation.len > len) {
const sl = @as([*]u8, @ptrFromInt(allocation.ptr))[0..allocation.len];
if (state.inner.rawResize(sl, allocation.log2_align, len, ret_addr)) {
defer _ = state.allocations.swapRemove(i);
return @ptrFromInt(allocation.ptr);
}
}
}
}
const p = state.inner.rawAlloc(len, log2_align, ret_addr);
return p;
}
fn resize(ctx: *anyopaque, buf: []u8, log2_align: u8, new_len: usize, ret_addr: usize) bool {
const state: *FreeListAllocator = @ptrCast(@alignCast(ctx));
return state.inner.rawResize(buf, log2_align, new_len, ret_addr);
}
fn free(ctx: *anyopaque, buf: []u8, log2_align: u8, ret_addr: usize) void {
const state: *FreeListAllocator = @ptrCast(@alignCast(ctx));
state.allocations.append(.{
.len = buf.len,
.ptr = @intFromPtr(buf.ptr),
.log2_align = log2_align,
}) catch state.inner.rawFree(buf, log2_align, ret_addr);
}
};
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