feature/7: Moving promise into repo

go.mod

@@ -2,10 +2,7 @@ module github.com/thinkdata-works/gocache
 
 go 1.18
 
-require (
-	github.com/stretchr/testify v1.8.3
-	github.com/thinkdata-works/gopromise v0.1.0
-)
+require github.com/stretchr/testify v1.8.3
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect

go.sum

@@ -4,8 +4,6 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/testify v1.8.3 h1:RP3t2pwF7cMEbC1dqtB6poj3niw/9gnV4Cjg5oW5gtY=
 github.com/stretchr/testify v1.8.3/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
-github.com/thinkdata-works/gopromise v0.1.0 h1:qVWnyufZfoMyeUr4DtdhQhmgXz9abFdGAHhCdipM3Pk=
-github.com/thinkdata-works/gopromise v0.1.0/go.mod h1:vec0Q1/jvqEZ7UutAfzRKYIiqEcj4/pAQOxLvnzxP3c=
 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=

pkg/gocache/cache.go

@@ -2,17 +2,15 @@ package gocache
 
 import (
 	"time"
-
-	"github.com/thinkdata-works/gopromise/pkg/promise"
 )
 
 type Cache[K comparable, V any] struct {
-	cache *partitionedCache[K, promise.Promise[V]]
+	cache *partitionedCache[K, Promise[V]]
 }
 
 func NewCache[K comparable, V any](partitionSize, totalPartitions int, cacheExpiry time.Duration) *Cache[K, V] {
 	return &Cache[K, V]{
-		cache: newPartitionedCached[K, promise.Promise[V]](
+		cache: newPartitionedCached[K, Promise[V]](
 			partitionSize, totalPartitions, cacheExpiry,
 		),
 	}
@@ -23,7 +21,7 @@ func (c *Cache[K, V]) HasKey(k K) (bool, error) {
 }
 
 func (c *Cache[K, V]) Get(k K, getter func() (*V, error)) (*V, error) {
-	valpromise, alreadyExists := c.cache.GetOrCreate(k, promise.NewPromise[V]())
+	valpromise, alreadyExists := c.cache.GetOrCreate(k, NewPromise[V]())
 	if alreadyExists {
 		val, err := valpromise.Wait()
 		if err != nil {

pkg/gocache/promise.go

@@ -0,0 +1,73 @@
+package gocache
+
+import (
+	"sync"
+	"time"
+)
+
+type future[V any] struct {
+	v   *V
+	err error
+}
+
+type Promise[V any] struct {
+	ch    chan future[V]
+	v     *V
+	err   error
+	mu    *sync.Mutex
+	count int
+	done  bool
+	start time.Time
+}
+
+func NewPromise[V any]() *Promise[V] {
+	return &Promise[V]{
+		ch:    make(chan future[V]),
+		start: time.Now(),
+		mu:    &sync.Mutex{},
+		done:  false,
+		count: 0,
+		v:     nil,
+		err:   nil,
+	}
+}
+
+func (p *Promise[V]) Wait() (*V, error) {
+	p.mu.Lock()
+	if p.done {
+		p.mu.Unlock()
+		return p.v, p.err
+	}
+	p.count++
+	p.mu.Unlock()
+
+	f := <-p.ch
+	return f.v, f.err
+}
+
+func (p *Promise[V]) fulfill(v *V, err error) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	if p.done {
+		// already fulfilled
+		return
+	}
+	p.done = true
+	p.v = v
+	p.err = err
+	for i := 0; i < p.count; i++ {
+		p.ch <- future[V]{
+			v:   v,
+			err: err,
+		}
+	}
+}
+
+func (p *Promise[V]) Resolve(v *V) {
+	p.fulfill(v, nil)
+}
+
+func (p *Promise[V]) Reject(err error) {
+	p.fulfill(nil, err)
+}