From 5a9e355df838648800201a2a0a63e3bc2df94102 Mon Sep 17 00:00:00 2001
From: jdl <jdl@laptop>
Date: Tue, 26 Jul 2022 14:02:53 +0200
Subject: [PATCH] wip

---
 go.mod              |  9 ++++++
 go.sum              |  6 ++++
 keyedmutex/mutex.go | 67 ++++++++++++++++++++++++++++++++++++++
 testconn/net.go     | 79 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 161 insertions(+)
 create mode 100644 go.mod
 create mode 100644 go.sum
 create mode 100644 keyedmutex/mutex.go
 create mode 100644 testconn/net.go

diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..aec7824
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,9 @@
+module git.crumpington.com/private/mdb
+
+go 1.18
+
+require (
+	github.com/google/btree v1.1.2
+	github.com/mattn/go-sqlite3 v1.14.14
+	golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..e0874d9
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,6 @@
+github.com/google/btree v1.1.2 h1:xf4v41cLI2Z6FxbKm+8Bu+m8ifhj15JuZ9sa0jZCMUU=
+github.com/google/btree v1.1.2/go.mod h1:qOPhT0dTNdNzV6Z/lhRX0YXUafgPLFUh+gZMl761Gm4=
+github.com/mattn/go-sqlite3 v1.14.14 h1:qZgc/Rwetq+MtyE18WhzjokPD93dNqLGNT3QJuLvBGw=
+github.com/mattn/go-sqlite3 v1.14.14/go.mod h1:NyWgC/yNuGj7Q9rpYnZvas74GogHl5/Z4A/KQRfk6bU=
+golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f h1:v4INt8xihDGvnrfjMDVXGxw9wrfxYyCjk0KbXjhR55s=
+golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
diff --git a/keyedmutex/mutex.go b/keyedmutex/mutex.go
new file mode 100644
index 0000000..699e4b1
--- /dev/null
+++ b/keyedmutex/mutex.go
@@ -0,0 +1,67 @@
+package keyedmutex
+
+import (
+	"container/list"
+	"sync"
+)
+
+type KeyedMutex[K comparable] struct {
+	mu       *sync.Mutex
+	waitList map[K]*list.List
+}
+
+func New[K comparable]() KeyedMutex[K] {
+	return KeyedMutex[K]{
+		mu:       new(sync.Mutex),
+		waitList: map[K]*list.List{},
+	}
+}
+
+func (m KeyedMutex[K]) Lock(key K) {
+	if ch := m.lock(key); ch != nil {
+		<-ch
+	}
+}
+
+func (m KeyedMutex[K]) lock(key K) chan struct{} {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if waitList, ok := m.waitList[key]; ok {
+		ch := make(chan struct{})
+		waitList.PushBack(ch)
+		return ch
+	}
+
+	m.waitList[key] = list.New()
+	return nil
+}
+
+func (m KeyedMutex[K]) TryLock(key K) bool {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if _, ok := m.waitList[key]; ok {
+		return false
+	}
+
+	m.waitList[key] = list.New()
+	return true
+}
+
+func (m KeyedMutex[K]) Unlock(key K) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	waitList, ok := m.waitList[key]
+	if !ok {
+		panic("unlock of unlocked mutex")
+	}
+
+	if waitList.Len() == 0 {
+		delete(m.waitList, key)
+	} else {
+		ch := waitList.Remove(waitList.Front()).(chan struct{})
+		ch <- struct{}{}
+	}
+}
diff --git a/testconn/net.go b/testconn/net.go
new file mode 100644
index 0000000..b2ab532
--- /dev/null
+++ b/testconn/net.go
@@ -0,0 +1,79 @@
+package testconn
+
+import (
+	"net"
+	"sync"
+	"time"
+)
+
+type Network struct {
+	lock sync.Mutex
+	// Current connections.
+	cConn net.Conn
+	sConn net.Conn
+
+	acceptQ chan net.Conn
+}
+
+func NewNetwork() *Network {
+	return &Network{
+		acceptQ: make(chan net.Conn, 1),
+	}
+}
+
+func (n *Network) Dial() net.Conn {
+	cc, sc := net.Pipe()
+	func() {
+		n.lock.Lock()
+		defer n.lock.Unlock()
+		if n.cConn != nil {
+			n.cConn.Close()
+			n.cConn = nil
+		}
+		select {
+		case n.acceptQ <- sc:
+			n.cConn = cc
+		default:
+			cc = nil
+		}
+	}()
+	return cc
+}
+
+func (n *Network) Accept() net.Conn {
+	var sc net.Conn
+	select {
+	case sc = <-n.acceptQ:
+	case <-time.After(time.Second):
+		return nil
+	}
+
+	func() {
+		n.lock.Lock()
+		defer n.lock.Unlock()
+		if n.sConn != nil {
+			n.sConn.Close()
+			n.sConn = nil
+		}
+		n.sConn = sc
+	}()
+	return sc
+}
+
+func (n *Network) CloseClient() {
+	n.lock.Lock()
+	defer n.lock.Unlock()
+	if n.cConn != nil {
+		n.cConn.Close()
+		n.cConn = nil
+	}
+}
+
+func (n *Network) CloseServer() {
+	n.lock.Lock()
+	defer n.lock.Unlock()
+	if n.sConn != nil {
+		n.sConn.Close()
+		n.sConn = nil
+	}
+}