chore: add tests and examples for mem.Pool

tokenizer/lattice/mem/doc.go

@@ -1,2 +1,2 @@
-// Package mem implements the memory utility.
+// Package mem implements the memory utility such as memory pool.
 package mem

tokenizer/lattice/mem/pool.go

@@ -5,11 +5,20 @@ import (
 )
 
 // Pool represents memory pool of T.
+//
+// It is suitable for managing temporary objects that can be individually saved
+// and retrieved (mem.Pool.Put and mem.Pool.Get).
+// Unlike variables or pointer variables, mem.Pool is safe for use by multiple
+// goroutines and no new memory will be allocated.
+//
+// It is a wrapper of sync.Pool to support generics and easy to use. For the
+// actual usage, see the example in the package documentation.
 type Pool[T any] struct {
 	internal *sync.Pool
 }
 
-// NewPool returns a memory pool of T.
+// NewPool returns a memory pool of T. f is a constructor of T and it is called
+// when the memory pool is empty.
 func NewPool[T any](f func() *T) Pool[T] {
 	return Pool[T]{
 		internal: &sync.Pool{

tokenizer/lattice/mem/pool_test.go

@@ -0,0 +1,119 @@
+package mem_test
+
+import (
+	"fmt"
+	"sync"
+	"testing"
+
+	"github.com/ikawaha/kagome/v2/tokenizer/lattice/mem"
+)
+
+func ExamplePool() {
+	type Foo struct {
+		Bar string
+	}
+
+	// newFoo is a constructor of Foo type.
+	newFoo := func() *Foo {
+		return &Foo{
+			Bar: "let the foo begin",
+		}
+	}
+
+	// Create a new memory pool of Foo type.
+	// If the memory pool is empty, it creates a new instance of Foo using newFoo.
+	bufPool := mem.NewPool[Foo](newFoo)
+
+	// Retrieve a Foo instance from the memory pool and print the current value
+	// of the Bar field.
+	a := bufPool.Get()
+	fmt.Println(a.Bar)
+
+	// Set the Bar field then put it back to the memory pool.
+	a.Bar = "buz"
+	bufPool.Put(a)
+
+	// Same as above but set a different value to the Bar field.
+	//
+	// This will overwrite the previous value. But note that this will not allocate
+	// new memory and is safe for use by multiple goroutines simultaneously.
+	// See the benchmark in the same test file.
+	b := bufPool.Get()
+	b.Bar = "qux"
+	bufPool.Put(b)
+
+	// Retrieve a Foo instance from the memory pool and print the current value
+	// of the Bar field.
+	c := bufPool.Get()
+	fmt.Println(c.Bar)
+	// Output:
+	// let the foo begin
+	// qux
+}
+
+// To benchmark run:
+//
+//	go test -benchmem -bench=Benchmark -count 5 ./tokenizer/lattice/mem
+func BenchmarkPool(b *testing.B) {
+	type Foo struct {
+		Bar int
+	}
+
+	bufPool := mem.NewPool[Foo](func() *Foo {
+		return new(Foo)
+	})
+
+	b.ResetTimer()
+
+	// Spawn 3 goroutines to get and put the Foo instance from the memory pool
+	// b.N times each.
+	//
+	// Note that mem.Pool is safe for use by multiple goroutines simultaneously
+	// and no new memory will be allocated.
+	var wg sync.WaitGroup
+
+	for i := 0; i < 3; i++ {
+		wg.Add(1)
+
+		go func(max int) {
+			defer wg.Done()
+
+			for i := 0; i < max; i++ {
+				a := bufPool.Get() // get
+				a.Bar += i         // increment
+				bufPool.Put(a)     // put
+			}
+		}(b.N)
+	}
+
+	wg.Wait()
+}
+
+// To fuzz test run:
+//
+//	go test -fuzz=Fuzz -fuzztime 1m ./tokenizer/lattice/mem/...
+func FuzzPool(f *testing.F) {
+	type Foo struct {
+		Bar string
+	}
+
+	bufPool := mem.NewPool[Foo](func() *Foo {
+		return new(Foo)
+	})
+
+	// Corpus variants/patterns to fuzz test.
+	f.Add("")
+	f.Add(" ")
+	f.Add("0123456789")
+	f.Add("!@#$%^&*()_+")
+	f.Add("short")
+	f.Add("短")
+	f.Add("this is a test with a long string")
+	f.Add("これは、いささか長いテスト用の文字列です。")
+
+	f.Fuzz(func(_ *testing.T, s string) {
+		a := bufPool.Get() // get
+		a.Bar += s         // append
+		bufPool.Put(a)     // put
+	})
+}