This content originally appeared on DEV Community and was authored by HexShift
Zig's allocator system gives developers the power to create custom memory strategies tailored to specific use cases. One powerful technique is the memory pool, which can dramatically reduce allocation overhead for frequently reused objects.
In this guide, we’ll walk through building a fixed-size memory pool in Zig — ideal for managing short-lived or repeated allocations without relying on the heap each time.
Step 1: What Is a Memory Pool?
A memory pool is a block of pre-allocated memory that you carve up manually. It's great for:
- 🚀 Performance-critical systems
- 🔁 Repeated short-lived allocations
- 💡 Avoiding fragmentation in embedded or constrained environments
Step 2: Defining the Pool Structure
Here’s a simple fixed-size pool for allocating structs:
const std = @import("std");
const MyStruct = struct {
x: i32,
y: i32,
};
const Pool = struct {
memory: [100]MyStruct,
used: [100]bool,
pub fn init() Pool {
return Pool{
.memory = undefined,
.used = [_]bool{false} ** 100,
};
}
pub fn alloc(self: *Pool) ?*MyStruct {
for (self.used) |*slot, i| {
if (!slot.*) {
slot.* = true;
return &self.memory[i];
}
}
return null; // Pool full
}
pub fn free(self: *Pool, ptr: *MyStruct) void {
const index = ptr - &self.memory[0];
self.used[index] = false;
}
};
Step 3: Using the Pool
pub fn main() void {
var pool = Pool.init();
const a = pool.alloc() orelse {
std.debug.print("Allocation failed\n", .{});
return;
};
a.* = MyStruct{ .x = 10, .y = 20 };
std.debug.print("Allocated struct: x={}, y={}\n", .{ a.x, a.y });
pool.free(a);
}
- We allocate manually from the pool.
- The
usedarray tracks which slots are in use. - No dynamic memory is used — it's all stack/static.
✅ Pros and ❌ Cons of Custom Pools
✅ Pros:
- ⚡ Extremely fast allocation/deallocation
- 🔁 Great for fixed-size object reuse
- 📦 No heap or runtime dependencies
❌ Cons:
- 🧱 Fixed size: must plan ahead
- 🧮 Manual tracking logic
- ❗ No automatic resizing or safety checks
Summary
Writing your own memory pool in Zig gives you a lightweight, deterministic way to manage memory for repeated structures. This pattern shines in games, embedded systems, and performance-critical tools where the cost of heap allocation is too high.
Explore different pool designs (e.g. freelists, stack allocators) and consider combining them with Zig’s allocator interfaces for more flexibility.
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This content originally appeared on DEV Community and was authored by HexShift
HexShift | Sciencx (2025-05-09T01:24:24+00:00) Implementing a Custom Memory Pool in Zig. Retrieved from https://www.scien.cx/2025/05/09/implementing-a-custom-memory-pool-in-zig/
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