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Embedded Memory Allocator in Rust

Embedded systems often have limited and predictable memory resources. A custom memory allocator tailored to the specific hardware and application needs can significantly improve performance and reduce fragmentation compared to using a general-purpose allocator like malloc. This challenge asks you to implement a simple, fixed-size block allocator in Rust suitable for an embedded environment.

Problem Description

You are tasked with creating a basic memory allocator for an embedded system. The allocator will manage a contiguous block of memory of a fixed size. It should provide functions to allocate and deallocate memory blocks within this region. The allocator should be simple, efficient, and suitable for environments where dynamic memory allocation is constrained.

What needs to be achieved:

  • Implement a struct FixedBlockAllocator that encapsulates a fixed-size memory buffer.
  • Provide methods for allocating a block of memory of a specified size within the buffer.
  • Provide a method for deallocating a previously allocated block.
  • Handle allocation failures gracefully (return None when allocation is not possible).
  • Prevent double-free errors and memory corruption.

Key Requirements:

  • Fixed-Size Buffer: The allocator manages a single, pre-allocated buffer of a fixed size.
  • First-Fit Allocation: Use a first-fit allocation strategy. When allocating, search for the first available block that is large enough.
  • No Fragmentation Handling: This is a simplified allocator; you do not need to implement defragmentation.
  • Safety: The allocator must be memory-safe and prevent common errors like double-free and out-of-bounds access.
  • No External Dependencies: The solution should only use the Rust standard library.

Expected Behavior:

  • allocate(size): Returns Some(pointer) if a block of the requested size can be allocated, where pointer is a pointer to the beginning of the allocated block. Returns None if no suitable block is available.
  • deallocate(pointer, size): Deallocates the block of memory pointed to by pointer with the given size. Returns true if the deallocation was successful, false otherwise (e.g., invalid pointer or size).
  • The allocator should maintain a list of free blocks within the buffer.

Edge Cases to Consider:

  • Allocation of a size larger than the remaining free space.
  • Allocation of a size equal to the remaining free space.
  • Deallocating a pointer that was not allocated by the allocator.
  • Deallocating a block with an incorrect size.
  • Double-freeing a block.
  • Allocating zero-sized blocks (should be handled gracefully, potentially returning Some(pointer) where pointer is the start of the buffer).

Examples

Example 1:

Input:
allocator = FixedBlockAllocator::new(1024);
size = 100;
allocated_ptr = allocator.allocate(size);
size2 = 50;
allocated_ptr2 = allocator.allocate(size2);

Output:
allocated_ptr: Some(*const u8)  (some address within the 1024-byte buffer)
allocated_ptr2: Some(*const u8) (some address within the remaining space)

Explanation:
The allocator successfully allocates two blocks of memory, 100 bytes and 50 bytes, within the 1024-byte buffer.

Example 2:

Input:
allocator = FixedBlockAllocator::new(1024);
size = 1024;
allocated_ptr = allocator.allocate(size);

Output:
allocated_ptr: None

Explanation:
The allocator cannot allocate a block of 1024 bytes because the entire buffer is already allocated.

Example 3: (Edge Case)

Input:
allocator = FixedBlockAllocator::new(1024);
size = 100;
allocated_ptr = allocator.allocate(size);
allocator.deallocate(allocated_ptr, size);
size2 = 200;
allocated_ptr2 = allocator.allocate(size2);

Output:
allocated_ptr2: Some(*const u8) (some address within the 1024-byte buffer)

Explanation:
After deallocating the initial block, the allocator can successfully allocate a new block of 200 bytes.

Constraints

  • The buffer size will be between 128 and 4096 bytes (inclusive).
  • The requested allocation size will be between 1 and half the buffer size (inclusive).
  • The deallocate function will be called with a valid pointer within the buffer (if the pointer was previously allocated).
  • The deallocate function will be called with the correct size of the allocated block.
  • The allocator should be reasonably efficient (avoid unnecessary copying or complex data structures). A simple linked list of free blocks is acceptable.

Notes

  • Consider using a Vec<bool> or similar data structure to track free/allocated blocks, or a linked list of free blocks.
  • Pay close attention to memory safety and prevent common allocation errors.
  • The pointer returned by allocate should be a raw pointer (*const u8) to avoid lifetime issues.
  • This is a simplified allocator; you do not need to implement advanced features like coalescing or defragmentation.
  • Focus on correctness and safety over extreme performance optimization. The goal is to demonstrate understanding of basic allocation concepts in a safe and efficient manner.
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