From c1fcf0416ed960b669b2a4194684e2dbb1749fd3 Mon Sep 17 00:00:00 2001
From: "C. McEnroe" <june@causal.agency>
Date: Mon, 27 Sep 2021 16:12:45 +0000
Subject: Call msync(2) after modifying tiles

Without it, changes aren't visible to a process read(2)'ing the
file until all mappings of the file are unmapped, on OpenBSD. There
is apparently no guarantee that they are visible on other systems
either. TIL.
---
 server.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/server.c b/server.c
index ee19ec8..435eefa 100644
--- a/server.c
+++ b/server.c
@@ -67,7 +67,7 @@ static struct Tile *tileGet(uint32_t tileX, uint32_t tileY) {
 	return tile;
 }
 
-static const struct Tile *tileAccess(uint32_t tileX, uint32_t tileY) {
+static struct Tile *tileAccess(uint32_t tileX, uint32_t tileY) {
 	struct Tile *tile = tileGet(tileX, tileY);
 	tile->accessTime = time(NULL);
 	tile->accessCount++;
@@ -81,6 +81,12 @@ static struct Tile *tileModify(uint32_t tileX, uint32_t tileY) {
 	return tile;
 }
 
+static struct Tile *tileSync(struct Tile *tile) {
+	int error = msync(tile, sizeof(*tile), MS_ASYNC);
+	if (error) err(EX_IOERR, "msync");
+	return tile;
+}
+
 enum { ClientsCap = 256 };
 static struct Client {
 	int fd;
@@ -107,7 +113,9 @@ clientSend(const struct Client *client, const struct ServerMessage *msg) {
 	ssize_t len = send(client->fd, msg, sizeof(*msg), 0);
 	if (len < 0) return -1;
 	if (msg->type == ServerTile) {
-		const struct Tile *tile = tileAccess(client->tileX, client->tileY);
+		const struct Tile *tile = tileSync(
+			tileAccess(client->tileX, client->tileY)
+		);
 		len = send(client->fd, tile, sizeof(*tile), 0);
 		if (len < 0) return -1;
 	}
@@ -251,6 +259,7 @@ static int clientPut(const struct Client *client, uint8_t color, uint8_t cell) {
 	struct Tile *tile = tileModify(client->tileX, client->tileY);
 	tile->colors[client->cellY][client->cellX] = color;
 	tile->cells[client->cellY][client->cellX] = cell;
+	tileSync(tile);
 	struct ServerMessage msg = {
 		.type = ServerPut,
 		.put = {
-- 
cgit 1.4.1