From 2814f266b00a52fa11a0b91d1a4424d64c47c859 Mon Sep 17 00:00:00 2001
From: Sergey Vilgelm <sergey@vilgelm.com>
Date: Tue, 23 May 2023 13:05:47 -0700
Subject: [PATCH] the code (#1)

---
 README.md    | 33 +++++++++++++++++++++-
 pool.go      | 37 ++++++++++++++++++++++++
 pool_test.go | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 148 insertions(+), 1 deletion(-)
 create mode 100644 pool.go
 create mode 100644 pool_test.go

diff --git a/README.md b/README.md
index f2152c3..51a1270 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,33 @@
 # gpool
-Generic Pool in Go
+Generic wrapper for sync.Pool in Go
+
+## Usage
+
+`int64` type
+```go
+p := Pool[int64]{New: func() int64 { return 42 }}
+x := p.Get()
+defer p.Put(x)
+fmt.Printf("x = (%T) %d", x, x)
+// Output: x = (int64) 42
+```
+
+`string` type
+```go
+p := Pool[string]{New: func() string { return "foo" }}
+x := p.Get()
+defer p.Put(x)
+fmt.Printf("x = (%T) %s", x, x)
+// Output: x = (string) foo
+```
+
+## Benchmarks
+
+```shell
+% go test -bench=. -benchmem ./...
+goos: darwin
+goarch: arm64
+pkg: github.com/sv-tools/gpool
+BenchmarkSyncPool-8     699275571                1.614 ns/op           0 B/op          0 allocs/op
+BenchmarkPool-8         647708158                1.732 ns/op           0 B/op          0 allocs/op
+```
diff --git a/pool.go b/pool.go
new file mode 100644
index 0000000..5a3989f
--- /dev/null
+++ b/pool.go
@@ -0,0 +1,37 @@
+package gpool
+
+import "sync"
+
+// Pool is generic drop-in replacement of `sync.Pool`
+type Pool[T any] struct {
+	sp sync.Pool
+
+	// New optionally specifies a function to generate
+	// a value when Get would otherwise return nil.
+	// It may not be changed concurrently with calls to Get.
+	New func() T
+}
+
+// Put adds x to the pool.
+func (p *Pool[T]) Put(x T) {
+	p.sp.Put(x)
+}
+
+// Get selects an arbitrary item from the Pool, removes it from the
+// Pool, and returns it to the caller.
+// Get may choose to ignore the pool and treat it as empty.
+// Callers should not assume any relation between values passed to Put and
+// the values returned by Get.
+//
+// If Get would otherwise return nil and p.New is non-nil, Get returns
+// the result of calling p.New.
+func (p *Pool[T]) Get() (item T) {
+	x := p.sp.Get()
+	if x == nil {
+		if p.New != nil {
+			return p.New()
+		}
+		return item
+	}
+	return x.(T)
+}
diff --git a/pool_test.go b/pool_test.go
new file mode 100644
index 0000000..296ebc2
--- /dev/null
+++ b/pool_test.go
@@ -0,0 +1,79 @@
+package gpool
+
+import (
+	"fmt"
+	"math/rand"
+	"sync"
+	"testing"
+)
+
+func TestPool(t *testing.T) {
+	p := Pool[int64]{}
+	x := p.Get()
+	if x != 0 {
+		t.Fatalf("expected x = 0, but got %d", x)
+	}
+	p.New = func() int64 {
+		// should return only a number which is greater than zero
+		v := rand.Int63()
+		for v <= 0 {
+			v = rand.Int63()
+		}
+		return v
+	}
+	x = p.Get()
+	if x == 0 {
+		t.Fatal("expected x != 0, but got 0")
+	}
+	p.Put(-1)
+	// getting until the pool returns -1 or fails by timeout
+	for x != -1 {
+		x = p.Get()
+	}
+}
+
+var benchmarkSyncPoolResult any
+
+func BenchmarkSyncPool(b *testing.B) {
+	p := sync.Pool{New: func() any { return 42 }}
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		var res any
+		for pb.Next() {
+			res = p.Get()
+			p.Put(res)
+		}
+		benchmarkSyncPoolResult = res
+	})
+}
+
+var benchmarkPoolResult int64
+
+func BenchmarkPool(b *testing.B) {
+	p := Pool[int64]{New: func() int64 { return 42 }}
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		var res int64
+		for pb.Next() {
+			res = p.Get()
+			p.Put(res)
+		}
+		benchmarkPoolResult = res
+	})
+}
+
+func ExamplePool_int64() {
+	p := Pool[int64]{New: func() int64 { return 42 }}
+	x := p.Get()
+	defer p.Put(x)
+	fmt.Printf("x = (%T) %d", x, x)
+	// Output: x = (int64) 42
+}
+
+func ExamplePool_string() {
+	p := Pool[string]{New: func() string { return "foo" }}
+	x := p.Get()
+	defer p.Put(x)
+	fmt.Printf("x = (%T) %s", x, x)
+	// Output: x = (string) foo
+}