From f1ffe9b4cd7eb76a2df033dbd592aff2200c0d19 Mon Sep 17 00:00:00 2001
From: June <june@jsts.xyz>
Date: Fri, 15 Aug 2025 21:36:23 +0200
Subject: [PATCH] parallelize retrieval of server version information

Parallelizing the retrieval of the server version information decreases
the program runtime, especially since the impact of slow responses and
timeouts is lowered greatly.
---
 main.go | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 52 insertions(+), 4 deletions(-)

diff --git a/main.go b/main.go
index 23baa9a..ceda106 100644
--- a/main.go
+++ b/main.go
@@ -7,6 +7,7 @@ import (
 	"os"
 	"sort"
 	"strings"
+	"sync"
 
 	"github.com/hashicorp/go-version"
 	"github.com/matrix-org/gomatrixserverlib/fclient"
@@ -15,6 +16,11 @@ import (
 	"maunium.net/go/mautrix/id"
 )
 
+type HomeserverServerVersionInfo struct {
+	Homeserver        string
+	ServerVersionInfo fclient.Version
+}
+
 type ServerPath struct {
 	MaxRoomVersion string
 	Server         string
@@ -36,6 +42,44 @@ var unknownServerVersionInfo = fclient.Version{
 	},
 }
 
+func getServerVersionInfoByHomeserver(homeservers []string, federationClient *fclient.Client) map[string](fclient.Version) {
+	homeserverChannel := make(chan string)
+	go func() {
+		for _, hs := range homeservers {
+			homeserverChannel <- hs
+		}
+		close(homeserverChannel)
+	}()
+
+	homeserverSVInfoChannel := make(chan HomeserverServerVersionInfo)
+	var wg sync.WaitGroup
+	const numHomeserverSVInfoReceivers = 100
+	wg.Add(numHomeserverSVInfoReceivers)
+	for i := 0; i < numHomeserverSVInfoReceivers; i++ {
+		go func() {
+			for hs := range homeserverChannel {
+				serverVersionInfo, err := federationClient.GetVersion(context.Background(), spec.ServerName(hs))
+				if err != nil {
+					serverVersionInfo = unknownServerVersionInfo
+				}
+				homeserverSVInfoChannel <- HomeserverServerVersionInfo{hs, serverVersionInfo}
+			}
+			wg.Done()
+		}()
+	}
+
+	go func() {
+		wg.Wait()
+		close(homeserverSVInfoChannel)
+	}()
+
+	serverVersionInfoByHomeserver := make(map[string](fclient.Version))
+	for homeserverSVInfo := range homeserverSVInfoChannel {
+		serverVersionInfoByHomeserver[homeserverSVInfo.Homeserver] = homeserverSVInfo.ServerVersionInfo
+	}
+	return serverVersionInfoByHomeserver
+}
+
 // Gets the maximum supported room version for the given server-version-pair.
 func getMaxRoomVersion(serverVersionInfo fclient.Version) string {
 	// Use only the first part of the version string as sometimes there are suffixes after a space, like " (<commit>)", which then can't be parsed.
@@ -235,6 +279,13 @@ func main() {
 		membersByHomeservers[key.Homeserver()]++
 	}
 
+	homeservers := make([]string, 0, len(membersByHomeservers))
+	for hs := range membersByHomeservers {
+		homeservers = append(homeservers, hs)
+	}
+
+	serverVersionInfoByHomeserver := getServerVersionInfoByHomeserver(homeservers, federationClient)
+
 	// Info map tree.
 	maxRoomVersionInfo := make(map[string](map[string](map[string](map[string]uint))))
 	// Member counters.
@@ -243,10 +294,7 @@ func main() {
 	membersByVersionPath := make(map[VersionPath]uint)
 
 	for key, value := range membersByHomeservers {
-		serverVersionInfo, err := federationClient.GetVersion(context.Background(), spec.ServerName(key))
-		if err != nil {
-			serverVersionInfo = unknownServerVersionInfo
-		}
+		serverVersionInfo := serverVersionInfoByHomeserver[key]
 
 		maxRoomVersion := getMaxRoomVersion(serverVersionInfo)