From 23800ecd863be7166ad37ebd3c3d8e88ab140b97 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ond=C5=99ej=20Sur=C3=BD?= <ondrej@isc.org>
Date: Mon, 29 Aug 2022 14:30:54 +0200
Subject: [PATCH] Add developer note for the libuv quirks

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+<!--
+Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+
+SPDX-License-Identifier: MPL-2.0
+
+This Source Code Form is subject to the terms of the Mozilla Public
+License, v. 2.0.  If a copy of the MPL was not distributed with this
+file, you can obtain one at https://mozilla.org/MPL/2.0/.
+
+See the COPYRIGHT file distributed with this work for additional
+information regarding copyright ownership.
+-->
+
+## Libuv Notes
+
+This document describes various notes related to the using of the libuv library.
+
+### Queueing Events onto the ``uv_loop_t``
+
+The upstream documentation on [the I/O
+loop](http://docs.libuv.org/en/v1.x/design.html#the-i-o-loop) describes the
+order in which are the various handles processed.  However, it does not describe
+the order in which the loop processes the events in the same buckets, and
+because it is counterintuitive, it is described here.
+
+When scheduling the events of the same class (f.e. ``uv_*_start()`` or
+``uv_close()``), the events are executed in the LIFO order (e.g. it's a stack,
+not a queue).  The reasoning for the upstream design choice is described in [the
+upstream issue](https://github.com/libuv/libuv/issues/3582).
+
+What does this means in practice?  F.e. when closing the handles:
+
+    uv_close(&handle1, callback1);
+	uv_close(&handle2, callback2);
+
+The ``callback2()`` will be called before the ``callback1()``, so if they are
+using the same resource, the resource can be freed in the ``callback1()`` and
+not in the ``callback2()``.
+
+Same applies f.e. to the ``uv_idle_t``, if you want the ``action1()`` to execute
+before ``action2()``, the valid code would be:
+
+    uv_idle_start(&idle2, action2);
+    uv_idle_start(&idle1, action1);
+
+which is really counterintuitive.