lru: init

lru/Makefile

@@ -0,0 +1,48 @@
+.DEFAULT_GOAL := help
+
+# ==================================================================================== #
+# HELPERS
+# ==================================================================================== #
+
+## help: print this help message
+.PHONY: help
+help:
+	@echo 'Usage:'
+	@sed -n 's/^##//p' ${MAKEFILE_LIST} | column -t -s ':' |  sed -e 's/^/ /'
+
+
+# ==================================================================================== #
+# QUALITY CONTROL
+# ==================================================================================== #
+
+## tidy: format code and tidy modfile
+.PHONY: tidy
+tidy:
+	go fmt ./...
+	go mod tidy -v
+
+## audit: run quality control checks
+.PHONY: audit
+audit:
+	go mod verify
+	go vet ./...
+	go run honnef.co/go/tools/cmd/staticcheck@latest -checks=all,-ST1000,-U1000 ./...
+	go run golang.org/x/vuln/cmd/govulncheck@latest ./...
+	go test -race -buildvcs -vet=off ./...
+	go run github.com/golangci/golangci-lint/cmd/golangci-lint@latest run -v ./...
+
+
+# ==================================================================================== #
+# DEVELOPMENT
+# ==================================================================================== #
+
+## test: run all tests
+.PHONY: test
+test:
+	go test -v -race -buildvcs ./...
+
+## test/cover: run all tests and display coverage
+.PHONY: test/cover
+test/cover:
+	go test -v -race -buildvcs -coverprofile=/tmp/coverage.out ./...
+	go tool cover -html=/tmp/coverage.out

lru/go.mod

@@ -0,0 +1,11 @@
+module lru
+
+go 1.21.6
+
+require github.com/stretchr/testify v1.8.4
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

lru/go.sum

@@ -0,0 +1,10 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

lru/lru.go

@@ -0,0 +1,106 @@
+package lru
+
+import (
+	"container/list"
+	"time"
+)
+
+type LRU[T any] struct {
+	queue    *list.List
+	items    map[string]*list.Element
+	capacity int
+}
+type item[T any] struct {
+	key   string
+	value *T
+	eol   time.Time
+}
+
+func New[T any](capacity int) *LRU[T] {
+	return &LRU[T]{
+		queue:    list.New(),
+		items:    make(map[string]*list.Element, capacity),
+		capacity: capacity,
+	}
+}
+
+func (lru *LRU[T]) Set(key string, value T, ttl time.Duration) (evicted bool) {
+	eol := time.Now().Add(ttl)
+
+	if element, ok := lru.items[key]; ok {
+		lru.queue.MoveToFront(element)
+		item := element.Value.(*item[T])
+		item.value = &value
+		item.eol = eol
+
+		return
+	}
+
+	if lru.queue.Len() == lru.capacity {
+		lru.evict()
+		evicted = true
+	}
+
+	item := &item[T]{
+		key:   key,
+		value: &value,
+		eol:   eol,
+	}
+
+	element := lru.queue.PushFront(item)
+	lru.items[item.key] = element
+
+	return
+}
+
+func (lru *LRU[T]) Get(name string) (value T, ok bool) {
+	element, ok := lru.items[name]
+	if !ok {
+		return value, false
+	}
+
+	item := element.Value.(*item[T])
+	if item.expired() {
+		lru.delete(element)
+
+		return value, false
+	}
+
+	lru.queue.MoveToFront(element)
+
+	return *item.value, true
+}
+
+func (lru *LRU[T]) evict() {
+	element := lru.queue.Back()
+	if element == nil {
+		return
+	}
+
+	for { // find first expired
+		item := element.Value.(*item[T])
+
+		if item.expired() {
+			lru.delete(element)
+
+			return
+		}
+
+		element = element.Prev()
+
+		if element == nil {
+			break // probably expired not found
+		}
+	}
+
+	lru.delete(lru.queue.Back()) // delete oldest if no one expired
+}
+
+func (lru *LRU[T]) delete(element *list.Element) {
+	lru.queue.Remove(element)
+	delete(lru.items, element.Value.(*item[T]).key)
+}
+
+func (i *item[T]) expired() bool {
+	return time.Now().After(i.eol)
+}

lru/lru_test.go

@@ -0,0 +1,78 @@
+package lru
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+	"time"
+)
+
+func TestTtl(t *testing.T) {
+	cache := New[int](1)
+
+	cache.Set("first", 1, 500*time.Millisecond)
+
+	value, ok := cache.Get("first")
+	assert.True(t, ok)
+	assert.Equal(t, 1, value)
+
+	time.Sleep(600 * time.Millisecond)
+
+	value, ok = cache.Get("first")
+	assert.False(t, ok)
+	assert.Equal(t, 0, value)
+}
+
+func TestEvictFirst(t *testing.T) {
+	cache := New[int](2)
+
+	assert.False(t, cache.Set("first", 1, 500*time.Millisecond))
+	assert.False(t, cache.Set("second", 2, 500*time.Millisecond))
+	assert.True(t, cache.Set("third", 3, 500*time.Millisecond))
+
+	_, ok := cache.Get("first")
+	assert.False(t, ok)
+}
+
+func TestEvictExpired(t *testing.T) {
+	cache := New[int](2)
+
+	assert.False(t, cache.Set("first", 1, 1000*time.Millisecond))
+	assert.False(t, cache.Set("second", 2, 100*time.Millisecond))
+
+	time.Sleep(200*time.Millisecond)
+
+	assert.True(t, cache.Set("third", 3, 1000*time.Millisecond))
+
+	var ok bool
+	_, ok = cache.Get("first")
+	assert.True(t, ok)
+	_, ok = cache.Get("third")
+	assert.True(t, ok)
+	_, ok = cache.Get("second")
+	assert.False(t, ok)
+}
+
+func TestSetExisted(t *testing.T) {
+	cache := New[int](2)
+
+	assert.False(t, cache.Set("first", 1, 200*time.Millisecond))
+	assert.False(t, cache.Set("second", 2, 500*time.Millisecond))
+
+	time.Sleep(100*time.Millisecond)
+
+	assert.False(t, cache.Set("first", 11, 1000*time.Millisecond))
+	assert.True(t, cache.Set("third", 3, 1000*time.Millisecond))
+
+	value, ok := cache.Get("first") // exists with updated ttl
+	assert.True(t, ok)
+	assert.Equal(t, 11, value)
+	_, ok = cache.Get("third")
+	assert.True(t, ok)
+	_, ok = cache.Get("second") // evicted
+	assert.False(t, ok)
+}
+
+func TestDummy(t *testing.T)  { // for coverage 100% coverage
+	cache := New[int](0)
+	cache.evict()
+}