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Memory management in Rust represents one of the language's most powerful features, combining safety with performance. I'll explore the advanced concepts and practical implementations that make Rust's memory management system unique and effective.

At its core, Rust's memory management relies on ownership rules and the borrow checker. These fundamental concepts enforce memory safety at compile time, eliminating common issues like null pointer dereferencing and data races.

The stack and heap allocation in Rust follows a deterministic pattern. Stack allocation happens automatically for fixed-size values, while heap allocation requires explicit handling through smart pointers like Box, Rc, and Arc.

let stack_value = 42;
let heap_value = Box::new(42);

Custom allocators provide granular control over memory management. Here's a basic implementation of a custom allocator:

use std::alloc::{GlobalAlloc, Layout};

struct CustomAllocator;

unsafe impl GlobalAlloc for CustomAllocator {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        let ptr = libc::malloc(layout.size()) as *mut u8;
        ptr
    }

    unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
        libc::free(ptr as *mut libc::c_void)
    }
}

#[global_allocator]
static ALLOCATOR: CustomAllocator = CustomAllocator;

Memory pools offer efficient allocation for objects of similar sizes. This implementation demonstrates a simple memory pool:

struct MemoryPool {
    chunks: Vec<Vec<u8>>,
    chunk_size: usize,
    free_list: Vec<usize>,
}

impl MemoryPool {
    fn new(chunk_size: usize) -> Self {
        MemoryPool {
            chunks: Vec::new(),
            chunk_size,
            free_list: Vec::new(),
        }
    }

    fn allocate(&mut self) -> Option<&mut [u8]> {
        if let Some(index) = self.free_list.pop() {
            return Some(&mut self.chunks[index]);
        }

        let mut chunk = Vec::with_capacity(self.chunk_size);
        chunk.resize(self.chunk_size, 0);
        self.chunks.push(chunk);
        Some(&mut self.chunks.last_mut()?[..])
    }

    fn deallocate(&mut self, index: usize) {
        self.free_list.push(index);
    }
}

Arena allocation provides efficient memory management for short-lived objects. Here's a basic arena allocator:

struct Arena {
    chunks: Vec<Vec<u8>>,
    current_chunk: usize,
    offset: usize,
}

impl Arena {
    fn new() -> Self {
        Arena {
            chunks: vec![Vec::with_capacity(4096)],
            current_chunk: 0,
            offset: 0,
        }
    }

    fn allocate(&mut self, size: usize) -> &mut [u8] {
        if self.offset + size > self.chunks[self.current_chunk].capacity() {
            self.chunks.push(Vec::with_capacity(4096));
            self.current_chunk += 1;
            self.offset = 0;
        }

        let start = self.offset;
        self.offset += size;
        &mut self.chunks[self.current_chunk][start..self.offset]
    }
}

Memory mapping enables efficient file handling. The following example demonstrates memory-mapped file operations:

use memmap2::MmapMut;
use std::fs::OpenOptions;

fn memory_mapped_file() -> std::io::Result<()> {
    let file = OpenOptions::new()
        .read(true)
        .write(true)
        .create(true)
        .open("data.bin")?;

    file.set_len(1024)?;

    let mut mmap = unsafe { MmapMut::map_mut(&file)? };

    mmap[0] = 42;
    mmap.flush()?;

    Ok(())
}

Placement new operations allow precise control over object placement in memory:

struct Aligned16<T>(T);

impl<T> Aligned16<T> {
    fn new(value: T) -> Self {
        let layout = Layout::new::<T>()
            .align_to(16)
            .expect("Failed to align");

        let ptr = unsafe {
            std::alloc::alloc(layout)
        };

        unsafe {
            std::ptr::write(ptr as *mut T, value);
            Aligned16(std::ptr::read(ptr as *const T))
        }
    }
}

Reference counting in Rust provides shared ownership with runtime checks:

use std::rc::Rc;
use std::cell::RefCell;

struct SharedData {
    value: RefCell<Vec<i32>>,
}

fn shared_memory() {
    let data = Rc::new(SharedData {
        value: RefCell::new(vec![1, 2, 3]),
    });

    let clone1 = Rc::clone(&data);
    let clone2 = Rc::clone(&data);

    clone1.value.borrow_mut().push(4);
    clone2.value.borrow_mut().push(5);
}

Smart pointers extend Rust's memory management capabilities:

use std::pin::Pin;
use std::marker::PhantomPinned;

struct PinnedData {
    data: String,
    _marker: PhantomPinned,
}

impl PinnedData {
    fn new(data: String) -> Pin<Box<Self>> {
        let pinned = Box::pin(PinnedData {
            data,
            _marker: PhantomPinned,
        });
        pinned
    }
}

Memory leaks can be prevented using drop implementations:

struct ResourceHandle {
    data: Vec<u8>,
}

impl Drop for ResourceHandle {
    fn drop(&mut self) {
        println!("Cleaning up resources");
        self.data.clear();
    }
}

Rust's memory management system combines these advanced features with zero-cost abstractions. The compiler ensures memory safety while maintaining performance through static analysis and ownership rules.

Understanding these concepts allows developers to create efficient, safe applications with precise control over memory usage. The combination of ownership rules, borrowing, and advanced allocation patterns makes Rust particularly suitable for systems programming and performance-critical applications.

These memory management features enable the development of complex systems without sacrificing safety or performance. The strict compile-time checks and explicit memory handling create reliable and efficient software while preventing common memory-related bugs.

By leveraging these advanced memory management techniques, developers can build robust applications that maintain both safety and performance. The system's flexibility allows for customization while ensuring memory safety through compile-time guarantees.

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