Implement an Arena Allocator for Bulk Deallocation

Bulk Free With One Reset

Arena allocators (also called region allocators) hand out slices from growing blocks and free everything when the arena resets. LLVM's BumpPtrAllocator, Rust's bumpalo, and many compilers use arenas per function or per compilation unit.

Block Chaining

When the current block fills, allocate a larger block, link it, and continue bumping. Reset walks blocks or reuses the first chunk.

c
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Great for AST nodes created during parse and thrown away after codegen
Thread-local arenas avoid synchronization on bump path
Do not store arena pointers past reset
Combine with a malloc fallback for rare huge allocations

Working Through the Exercise

Keep the relevant documentation open while you implement. When your output disagrees with the reference, trace one failing case by hand before changing random lines.

Trace first: walk one failing input step by step
Read the manual: skim the official doc for the mechanism named in this task
Compare baselines: save measurements from the prior step so speedups are honest

Why for this exercise

You will implement a multi-block arena with reset and measure allocation throughput. This exercise requires using the arena for a batch of objects then reclaiming all with one reset call.

Implement an arena allocator in C.

Requirements:

Define Arena struct with current block, offset, capacity, and block list
Implement arena_create(initial_size) that allocates the first block
Implement arena_alloc(arena, size, align) that bumps the pointer with alignment
Support alignment requirements (power of 2)
Implement arena_grow(arena, new_size) for when current block is full
Implement arena_reset(arena) to reset offset to 0 for reuse
Implement arena_destroy(arena) to free all blocks
Track total bytes allocated and peak usage
Demonstrate allocating structs, arrays, and strings

Test:

Show arena creation
Show multiple allocations
Show alignment working
Show reset and destroy
Show usage statistics

Bulk Free With One Reset

Block Chaining

When the current block fills, allocate a larger block, link it, and continue bumping. Reset walks blocks or reuses the first chunk.

c
Loading…

Great for AST nodes created during parse and thrown away after codegen
Thread-local arenas avoid synchronization on bump path
Do not store arena pointers past reset
Combine with a malloc fallback for rare huge allocations

Working Through the Exercise

Keep the relevant documentation open while you implement. When your output disagrees with the reference, trace one failing case by hand before changing random lines.

Trace first: walk one failing input step by step
Read the manual: skim the official doc for the mechanism named in this task
Compare baselines: save measurements from the prior step so speedups are honest

Why for this exercise

You will implement a multi-block arena with reset and measure allocation throughput. This exercise requires using the arena for a batch of objects then reclaiming all with one reset call.

Implement an arena allocator in C.

Requirements:

Define Arena struct with current block, offset, capacity, and block list
Implement arena_create(initial_size) that allocates the first block
Implement arena_alloc(arena, size, align) that bumps the pointer with alignment
Support alignment requirements (power of 2)
Implement arena_grow(arena, new_size) for when current block is full
Implement arena_reset(arena) to reset offset to 0 for reuse
Implement arena_destroy(arena) to free all blocks
Track total bytes allocated and peak usage
Demonstrate allocating structs, arrays, and strings

Test:

Show arena creation
Show multiple allocations
Show alignment working
Show reset and destroy
Show usage statistics

Topic Overview

Bulk Free With One Reset

Block Chaining

Working Through the Exercise

Why for this exercise

Implementation Task

Progressive Hints

Resources

Open Source

Implement an Arena Allocator for Bulk Deallocation

Topic Overview

Bulk Free With One Reset

Block Chaining

Working Through the Exercise

Why for this exercise

Implementation Task

Progressive Hints

Resources

Open Source