From f2b24479eed677677cc7615fa120d0d0cb87b389 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Mon, 31 Mar 2025 23:51:51 -0700
Subject: [PATCH] EventLoop: let the allocator do its job

to bucket and free fiber allocations
---
 lib/std/Io/EventLoop.zig | 33 ++++++++-------------------------
 1 file changed, 8 insertions(+), 25 deletions(-)

diff --git a/lib/std/Io/EventLoop.zig b/lib/std/Io/EventLoop.zig
index 37ad088b6d..067ed04c3d 100644
--- a/lib/std/Io/EventLoop.zig
+++ b/lib/std/Io/EventLoop.zig
@@ -26,7 +26,6 @@ const Thread = struct {
     idle_context: Context,
     current_context: *Context,
     ready_queue: ?*Fiber,
-    free_queue: ?*Fiber,
     io_uring: IoUring,
     idle_search_index: u32,
     steal_ready_search_index: u32,
@@ -78,12 +77,6 @@ const Fiber = struct {
     );
 
     fn allocate(el: *EventLoop) error{OutOfMemory}!*Fiber {
-        const thread: *Thread = .current();
-        if (thread.free_queue) |free_fiber| {
-            thread.free_queue = free_fiber.queue_next;
-            free_fiber.queue_next = null;
-            return free_fiber;
-        }
         return @ptrCast(try el.gpa.alignedAlloc(u8, @alignOf(Fiber), allocation_size));
     }
 
@@ -129,18 +122,15 @@ const Fiber = struct {
         )) |cancel_thread| assert(cancel_thread == Thread.canceling);
     }
 
-    fn recycle(fiber: *Fiber) void {
-        const thread: *Thread = .current();
-        std.log.debug("recyling {*}", .{fiber});
-        assert(fiber.queue_next == null);
-        //@memset(fiber.allocatedSlice(), undefined); // (race)
-        fiber.queue_next = thread.free_queue;
-        thread.free_queue = fiber;
-    }
-
     const Queue = struct { head: *Fiber, tail: *Fiber };
 };
 
+fn recycle(el: *EventLoop, fiber: *Fiber) void {
+    std.log.debug("recyling {*}", .{fiber});
+    assert(fiber.queue_next == null);
+    el.gpa.free(fiber.allocatedSlice());
+}
+
 pub fn io(el: *EventLoop) Io {
     return .{
         .userdata = el,
@@ -207,7 +197,6 @@ pub fn init(el: *EventLoop, gpa: Allocator) !void {
         },
         .current_context = &main_fiber.context,
         .ready_queue = null,
-        .free_queue = null,
         .io_uring = try IoUring.init(io_uring_entries, 0),
         .idle_search_index = 1,
         .steal_ready_search_index = 1,
@@ -227,11 +216,6 @@ pub fn deinit(el: *EventLoop) void {
     const allocated_ptr: [*]align(@alignOf(Thread)) u8 = @alignCast(@ptrCast(el.threads.allocated.ptr));
     const idle_stack_end_offset = std.mem.alignForward(usize, el.threads.allocated.len * @sizeOf(Thread) + idle_stack_size, std.heap.page_size_max);
     for (el.threads.allocated[1..active_threads]) |*thread| thread.thread.join();
-    for (el.threads.allocated[0..active_threads]) |*thread| while (thread.free_queue) |free_fiber| {
-        thread.free_queue = free_fiber.queue_next;
-        free_fiber.queue_next = null;
-        el.gpa.free(free_fiber.allocatedSlice());
-    };
     el.gpa.free(allocated_ptr[0..idle_stack_end_offset]);
     el.* = undefined;
 }
@@ -343,7 +327,6 @@ fn schedule(el: *EventLoop, thread: *Thread, ready_queue: Fiber.Queue) void {
             .idle_context = undefined,
             .current_context = &new_thread.idle_context,
             .ready_queue = ready_queue.head,
-            .free_queue = null,
             .io_uring = IoUring.init(io_uring_entries, 0) catch |err| {
                 @atomicStore(u32, &el.threads.reserved, new_thread_index, .release);
                 // no more access to `thread` after giving up reservation
@@ -501,7 +484,7 @@ const SwitchMessage = struct {
                 el.schedule(thread, .{ .head = prev_fiber, .tail = prev_fiber });
             },
             .recycle => |fiber| {
-                fiber.recycle();
+                el.recycle(fiber);
             },
             .register_awaiter => |awaiter| {
                 const prev_fiber: *Fiber = @alignCast(@fieldParentPtr("context", message.contexts.prev));
@@ -795,7 +778,7 @@ fn @"await"(
     if (@atomicLoad(?*Fiber, &future_fiber.awaiter, .acquire) != Fiber.finished)
         event_loop.yield(null, .{ .register_awaiter = &future_fiber.awaiter });
     @memcpy(result, future_fiber.resultBytes(result_alignment));
-    future_fiber.recycle();
+    event_loop.recycle(future_fiber);
 }
 
 fn cancel(