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use std::alloc::{GlobalAlloc, Layout, System};
use std::sync::atomic::{AtomicUsize, Ordering::SeqCst};

#[derive(Debug)]
pub struct CountingAllocator {
    counter: AtomicUsize,
}

impl CountingAllocator {
    pub const fn new() -> Self {
        Self {
            counter: AtomicUsize::new(0),
        }
    }

    pub fn current_usage(&self) -> usize {
        self.counter.load(SeqCst)
    }
}

unsafe impl GlobalAlloc for CountingAllocator {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        let ret = System.alloc(layout);
        if !ret.is_null() {
            self.counter.fetch_add(layout.size(), SeqCst);
        }
        return ret;
    }

    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        System.dealloc(ptr, layout);
        self.counter.fetch_sub(layout.size(), SeqCst);
    }
}