From 884b1423a4e33323b28d97b7458bade9a36acce9 Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Tue, 7 Jan 2025 21:34:18 -0800
Subject: [PATCH] std.heap.memory_pool: make preheat() usable after init()

---
 lib/std/heap/memory_pool.zig | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/lib/std/heap/memory_pool.zig b/lib/std/heap/memory_pool.zig
index 5bfc4a60f6..6b9abfd8dc 100644
--- a/lib/std/heap/memory_pool.zig
+++ b/lib/std/heap/memory_pool.zig
@@ -69,17 +69,7 @@ pub fn MemoryPoolExtra(comptime Item: type, comptime pool_options: Options) type
         pub fn initPreheated(allocator: std.mem.Allocator, initial_size: usize) MemoryPoolError!Pool {
             var pool = init(allocator);
             errdefer pool.deinit();
-
-            var i: usize = 0;
-            while (i < initial_size) : (i += 1) {
-                const raw_mem = try pool.allocNew();
-                const free_node = @as(NodePtr, @ptrCast(raw_mem));
-                free_node.* = Node{
-                    .next = pool.free_list,
-                };
-                pool.free_list = free_node;
-            }
-
+            try pool.preheat(initial_size);
             return pool;
         }
 
@@ -89,6 +79,21 @@ pub fn MemoryPoolExtra(comptime Item: type, comptime pool_options: Options) type
             pool.* = undefined;
         }
 
+        /// Preheats the memory pool by pre-allocating `size` items.
+        /// This allows up to `size` active allocations before an
+        /// `OutOfMemory` error might happen when calling `create()`.
+        pub fn preheat(pool: *Pool, size: usize) MemoryPoolError!void {
+            var i: usize = 0;
+            while (i < size) : (i += 1) {
+                const raw_mem = try pool.allocNew();
+                const free_node = @as(NodePtr, @ptrCast(raw_mem));
+                free_node.* = Node{
+                    .next = pool.free_list,
+                };
+                pool.free_list = free_node;
+            }
+        }
+
         pub const ResetMode = std.heap.ArenaAllocator.ResetMode;
 
         /// Resets the memory pool and destroys all allocated items.