From 96c62ab9258ef0be8dd56af8207721d958c3776b Mon Sep 17 00:00:00 2001
From: Erik Brakkee <erik@brakkee.org>
Date: Thu, 15 Aug 2024 21:25:30 +0200
Subject: [PATCH] concurrency for the expiry time

---
 cmd/templaterender/render.go        |  2 +-
 pkg/models/state.go                 | 18 +++++++++++++++++-
 pkg/server/matchmaker/matchmaker.go |  4 ++--
 pkg/server/templates/sessions.templ |  4 ++--
 4 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/cmd/templaterender/render.go b/cmd/templaterender/render.go
index 42e70f7..bcffddb 100644
--- a/cmd/templaterender/render.go
+++ b/cmd/templaterender/render.go
@@ -92,8 +92,8 @@ func main() {
 				OS:       "linux",
 				Shell:    "/bin/bash",
 			},
-			ExpiryTime: time.Now().In(japan).Add(10 * time.Minute),
 		}
+		agent.SetExpiryTime(time.Now().In(japan).Add(10 * time.Minute))
 		state.Agents.Put(agent.Guid, &agent)
 		client := models.Client{
 			Guid:        models.ClientGuid(strconv.Itoa(rand.Int())),
diff --git a/pkg/models/state.go b/pkg/models/state.go
index 880f533..0b30a4d 100644
--- a/pkg/models/state.go
+++ b/pkg/models/state.go
@@ -3,9 +3,16 @@ package models
 import (
 	"git.wamblee.org/converge/pkg/comms"
 	"git.wamblee.org/converge/pkg/support/collections"
+	"sync/atomic"
 	"time"
 )
 
+// Concurrency design:
+// 1. State is immutable
+// 2. The MatchMakers uses copy-on-write and never modifies a state directly.
+// 3. the matchmaker modifies the expiry time of the agent. This is dealt with using the
+//    sync/atomic package by storing the expiry time as an int64 using time.Time.UnixNano()
+
 type RendezVousId string
 type AgentGuid string
 type ClientGuid string
@@ -22,7 +29,16 @@ type Agent struct {
 	// TODO add remote address.
 
 	EnvironmentInfo comms.EnvironmentInfo
-	ExpiryTime      time.Time
+	expiryTime      int64
+}
+
+func (agent *Agent) SetExpiryTime(t time.Time) {
+	atomic.StoreInt64(&agent.expiryTime, t.UnixNano())
+}
+
+func (agent *Agent) GetExpiryTime() time.Time {
+	t := atomic.LoadInt64(&agent.expiryTime)
+	return time.Unix(0, t)
 }
 
 type Client struct {
diff --git a/pkg/server/matchmaker/matchmaker.go b/pkg/server/matchmaker/matchmaker.go
index 4e570b4..75f9044 100644
--- a/pkg/server/matchmaker/matchmaker.go
+++ b/pkg/server/matchmaker/matchmaker.go
@@ -56,7 +56,7 @@ func (converge *MatchMaker) Register(publicId models.RendezVousId, conn io.ReadW
 				converge.admin.SetSessionType(models.ClientId(session.ClientId), models.SessionType(session.SessionType))
 			},
 			func(expiry comms.ExpiryTimeUpdate) {
-				agent.ExpiryTime = expiry.ExpiryTime
+				agent.SetExpiryTime(expiry.ExpiryTime)
 				converge.logStatus()
 			})
 	}()
@@ -137,7 +137,7 @@ func logStatusImpl(admin *models.State, notifier Notifier) {
 	for agent := range admin.Agents.RangeValues() {
 		lines = append(lines, fmt.Sprintf(format, agent.PublicId,
 			agent.StartTime.Format(time.DateTime),
-			agent.ExpiryTime.Format(time.DateTime),
+			agent.GetExpiryTime().Format(time.DateTime),
 			agent.EnvironmentInfo.Username,
 			agent.EnvironmentInfo.Hostname,
 			agent.EnvironmentInfo.OS))
diff --git a/pkg/server/templates/sessions.templ b/pkg/server/templates/sessions.templ
index 777d0b8..f8e7937 100644
--- a/pkg/server/templates/sessions.templ
+++ b/pkg/server/templates/sessions.templ
@@ -39,7 +39,7 @@ templ State(state *models.State, location *time.Location) {
            <tr>
                <th>rendez-vous id</th>
                <th>start time</th>
-               <th>expiry time</th>
+               <th> time</th>
                <th>username</th>
                <th>host</th>
                <th>os</th>
@@ -50,7 +50,7 @@ templ State(state *models.State, location *time.Location) {
            <tr>
                <td>{string(agent.PublicId)}</td>
                <td>{agent.StartTime.In(location).Format(time.DateTime)}</td>
-               <td>{agent.ExpiryTime.In(location).Format(time.DateTime)}</td>
+               <td>{agent.GetExpiryTime().In(location).Format(time.DateTime)}</td>
                <td>{agent.EnvironmentInfo.Username}</td>
                <td>{agent.EnvironmentInfo.Hostname}</td>
                <td>{agent.EnvironmentInfo.OS}</td>