initial implement

.github/workflows/test.yaml

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+name: test
+on:
+  push:
+    branches:
+    - "**"
+  pull_request: {}
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+        - ubuntu-latest
+        - macOS-latest
+        - windows-latest
+    steps:
+    - name: setup go
+      uses: actions/setup-go@v1
+      with:
+        go-version: 1.x
+    - name: checkout
+      uses: actions/checkout@v1
+      with:
+        fetch-depth: 1
+    - name: lint
+      run: |
+        GO111MODULE=off GOBIN=$(pwd)/bin go get golang.org/x/lint/golint
+        bin/golint -set_exit_status ./...
+      if: "matrix.os == 'ubuntu-latest' || matrix.os == 'macOS-latest'"
+    - name: test
+      run: go test -coverprofile coverage.out -covermode atomic ./...
+    - name: Convert coverage to lcov
+      uses: jandelgado/gcov2lcov-action@v1.0.0
+      with:
+        infile: coverage.out
+        outfile: coverage.lcov
+      if: "matrix.os == 'ubuntu-latest'"
+    - name: Coveralls
+      uses: coverallsapp/github-action@master
+      with:
+        github-token: ${{ secrets.github_token }}
+        path-to-lcov: coverage.lcov
+      if: "matrix.os == 'ubuntu-latest'"

.gitignore

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+.*
+!.gitignore
+!.github

LICENSE

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+Copyright (c) 2020 Songmu
+
+MIT License
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Makefile

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+u := $(if $(update),-u)
+
+export GO111MODULE=on
+
+.PHONY: deps
+deps:
+	go get ${u} -d
+	go mod tidy
+
+.PHONY: devel-deps
+devel-deps:
+	sh -c '\
+      tmpdir=$$(mktemp -d); \
+      cd $$tmpdir; \
+      go get ${u} \
+        golang.org/x/lint/golint \
+        github.com/Songmu/godzil/cmd/godzil; \
+      rm -rf $$tmpdir'
+
+.PHONY: test
+test:
+	go test
+
+.PHONY: lint
+lint: devel-deps
+	golint -set_exit_status
+
+.PHONY: release
+release: devel-deps
+	godzil release

README.md

@@ -0,0 +1,32 @@
+smartcache
+=======
+
+[![Test Status](https://github.com/Songmu/smartcache/workflows/test/badge.svg?branch=master)][actions]
+[![Coverage Status](https://coveralls.io/repos/Songmu/smartcache/badge.svg?branch=master)][coveralls]
+[![MIT License](http://img.shields.io/badge/license-MIT-blue.svg?style=flat-square)][license]
+[![GoDoc](https://godoc.org/github.com/Songmu/smartcache?status.svg)][godoc]
+
+[actions]: https://github.com/Songmu/smartcache/actions?workflow=test
+[coveralls]: https://coveralls.io/r/Songmu/smartcache?branch=master
+[license]: https://github.com/Songmu/smartcache/blob/master/LICENSE
+[godoc]: https://godoc.org/github.com/Songmu/smartcache
+
+smartcache short description
+
+## Synopsis
+
+```go
+// simple usage here
+```
+
+## Description
+
+## Installation
+
+```console
+% go get github.com/Songmu/smartcache
+```
+
+## Author
+
+[Songmu](https://github.com/Songmu)

go.mod

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+module github.com/Songmu/smartcache
+
+go 1.13
+
+require (
+	github.com/Songmu/flextime v0.0.6
+	golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a
+)

go.sum

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+github.com/Songmu/flextime v0.0.6 h1:q9uTNwKY014E0AmCGOFt+0AaI5OXRty8gAalRyXdn9c=
+github.com/Songmu/flextime v0.0.6/go.mod h1:ofUSZ/qj7f1BfQQ6rEH4ovewJ0SZmLOjBF1xa8iE87Q=
+golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a h1:WXEvlFVvvGxCJLG6REjsT03iWnKLEWinaScsxF2Vm2o=
+golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=

smartcache.go

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+package smartcache
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"github.com/Songmu/flextime"
+	"golang.org/x/sync/singleflight"
+)
+
+// Cache for cache
+type Cache struct {
+	expire     time.Duration
+	softExpire time.Duration
+	generator  func(context.Context) (interface{}, error)
+
+	group singleflight.Group
+
+	mu             sync.RWMutex
+	value          interface{}
+	nextSoftExpire time.Time
+	nextExpire     time.Time
+}
+
+// New returns new Cache
+func New(expire, softExpire time.Duration, gen func(context.Context) (interface{}, error)) *Cache {
+	return &Cache{
+		expire:     expire,
+		softExpire: softExpire,
+		generator:  gen,
+	}
+}
+
+func (ca *Cache) renew(ctx context.Context) (interface{}, error) {
+	val, err, _ := ca.group.Do("renew", func() (interface{}, error) {
+		val, err := ca.generator(ctx)
+		if err == nil {
+			now := flextime.Now()
+			ca.mu.Lock()
+			ca.value = val
+			if ca.softExpire > 0 {
+				ca.nextSoftExpire = now.Add(ca.softExpire)
+			}
+			ca.nextExpire = now.Add(ca.expire)
+			ca.mu.Unlock()
+		}
+		return val, err
+	})
+	return val, err
+}
+
+// Get the cached value
+func (ca *Cache) Get(ctx context.Context) (interface{}, error) {
+	now := flextime.Now()
+	ca.mu.RLock()
+	currVal := ca.value
+	softExpire := ca.nextSoftExpire
+	expire := ca.nextExpire
+	ca.mu.RUnlock()
+
+	if now.After(expire) {
+		return ca.renew(ctx)
+	}
+	if !softExpire.IsZero() && now.After(softExpire) {
+		go ca.renew(ctx)
+	}
+	return currVal, nil
+}

smartcache_test.go

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+package smartcache_test
+
+import (
+	"context"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/Songmu/flextime"
+	"github.com/Songmu/smartcache"
+)
+
+func TestCache_Get(t *testing.T) {
+	now := flextime.Now()
+	defer flextime.Fix(now)()
+
+	var counter int
+	ca := smartcache.New(10*time.Second, time.Second, func(ctx context.Context) (interface{}, error) {
+		// Actually time.Sleep instead of flextime to emulate long running operations
+		time.Sleep(50 * time.Millisecond)
+		counter++
+		return counter, nil
+	})
+
+	t.Run("create new cache", func(t *testing.T) {
+		v, err := ca.Get(context.Background())
+		if err != nil {
+			t.Errorf("error should be nil, but: %s", err)
+		}
+		if v.(int) != 1 {
+			t.Errorf("value should be 1, but %v", v)
+		}
+	})
+
+	t.Run("get from cache", func(t *testing.T) {
+		v, err := ca.Get(context.Background())
+		if err != nil {
+			t.Errorf("error should be nil, but: %s", err)
+		}
+		if v.(int) != 1 {
+			t.Errorf("value should be 1, but %v", v)
+		}
+	})
+
+	t.Run("soft expire and renew internal value", func(t *testing.T) {
+		flextime.Sleep(2 * time.Second)
+		// check the concurrent cache updates won't conflict
+		var (
+			wg   = sync.WaitGroup{}
+			para = 10
+		)
+		wg.Add(para)
+		for i := 0; i < para; i++ {
+			go func() {
+				defer wg.Done()
+				ca.Get(context.Background())
+			}()
+		}
+		wg.Wait()
+		v, err := ca.Get(context.Background())
+		if err != nil {
+			t.Errorf("error should be nil, but: %s", err)
+		}
+		if v.(int) != 1 {
+			t.Errorf("value should be 1, but %v", v)
+		}
+	})
+
+	t.Run("wait for internal value update", func(t *testing.T) {
+		time.Sleep(55 * time.Millisecond) // use real time.Sleep for waiting cache update
+		v, err := ca.Get(context.Background())
+		if err != nil {
+			t.Errorf("error should be nil, but: %s", err)
+		}
+		if v.(int) != 2 {
+			t.Errorf("value should be 2, but %v", v)
+		}
+	})
+
+	t.Run("hard expire", func(t *testing.T) {
+		flextime.Sleep(11 * time.Second)
+		v, err := ca.Get(context.Background())
+		if err != nil {
+			t.Errorf("error should be nil, but: %s", err)
+		}
+		if v.(int) != 3 {
+			t.Errorf("value should be 3, but %v", v)
+		}
+	})
+}

version.go

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+package smartcache
+
+const version = "0.0.0"