From 9c31e89630080df375363482fe9e9938b66b43f5 Mon Sep 17 00:00:00 2001
From: Drew DeVault <sir@cmpwn.com>
Date: Fri, 20 Oct 2023 09:16:30 +0200
Subject: [PATCH] add ev::do

---
 ev/+linux/loop.ha | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++

diff --git a/ev/+linux/loop.ha b/ev/+linux/loop.ha
index 06c04c3ec127358874129b5a16f65de2bc420b72..2716907f3136a3fac8eed173ca933da3e1632e82 100644
--- a/ev/+linux/loop.ha
+++ b/ev/+linux/loop.ha
@@ -5,9 +5,19 @@ use time;
 use types;
 use unix::signal;
 
+// Dispatch callback. See [[ondispatch]].
+export type dispatchcb = fn(loop: *loop, user: nullable *opaque) void;
+
+export type ondispatch = struct {
+	cb: *dispatchcb,
+	user: nullable *opaque,
+	loop: *loop,
+};
+
 export type loop = struct {
 	fd: io::file,
 	events: []rt::epoll_event,
+	dispatch: []*ondispatch,
 	stop: bool,
 };
 
@@ -30,6 +40,7 @@ 			data = rt::epoll_data {
 				fd = 0,
 			}
 		}...], 256),
+		dispatch = [],
 		stop = false,
 	};
 };
@@ -50,6 +61,35 @@ export fn loop_file(loop: *loop) io::file = {
 	return loop.fd;
 };
 
+// Registers a callback to be invoked before the event loop dispatches pending
+// I/O requests. The callback may schedule additional I/O requests to be
+// processed in this batch.
+export fn do(
+	loop: *loop,
+	cb: *dispatchcb,
+	user: nullable *opaque,
+) req = {
+	const dispatch = alloc(ondispatch {
+		cb = cb,
+		user = user,
+		loop = loop,
+	});
+	append(loop.dispatch, dispatch);
+	return mkreq(&do_cancel, dispatch);
+};
+
+fn do_cancel(req: *req) void = {
+	const dispatch = req.user: *ondispatch;
+	const loop = dispatch.loop;
+	for (let i = 0z; i < len(loop.dispatch); i += 1) {
+		if (loop.dispatch[i] == dispatch) {
+			delete(loop.dispatch[i]);
+			break;
+		};
+	};
+	free(dispatch);
+};
+
 // Dispatches the event loop, waiting for new events and calling their callbacks
 // as appropriate.
 //
@@ -74,6 +114,16 @@ 	};
 	if (loop.stop) {
 		return false;
 	};
+
+	let todo = loop.dispatch;
+	loop.dispatch = [];
+	for (let i = 0z; i < len(todo); i += 1) {
+		const dispatch = todo[i];
+		dispatch.cb(loop, dispatch.user);
+		free(dispatch);
+	};
+	free(todo);
+
 	if (len(loop.events) == 0) {
 		return true;
 	};

-- 
2.48.1