chore: reorganize the structure of internal packages

internal/sync/spinlock.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by an MIT-style
 // license that can be found in the LICENSE file.
 
-package internal
+package sync
 
 import (
 	"runtime"

internal/sync/spinlock_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by an MIT-style
 // license that can be found in the LICENSE file.
 
-package internal
+package sync
 
 import (
 	"runtime"
@@ -14,12 +14,11 @@ import (
 /*
 Benchmark result for three types of locks:
 	goos: darwin
-	goarch: amd64
-	pkg: github.com/panjf2000/ants/v2/internal
-	cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
-	BenchmarkMutex-12              	20549502	        71.84 ns/op	       0 B/op	       0 allocs/op
-	BenchmarkSpinLock-12           	58629697	        20.02 ns/op	       0 B/op	       0 allocs/op
-	BenchmarkBackOffSpinLock-12    	72523454	        15.74 ns/op	       0 B/op	       0 allocs/op
+	goarch: arm64
+	pkg: github.com/panjf2000/ants/v2/internal/sync
+	BenchmarkMutex-10              	10452573	       111.1 ns/op	       0 B/op	       0 allocs/op
+	BenchmarkSpinLock-10           	58953211	        18.01 ns/op	       0 B/op	       0 allocs/op
+	BenchmarkBackOffSpinLock-10    	100000000	        10.81 ns/op	       0 B/op	       0 allocs/op
 */
 
 type originSpinLock uint32

pool.go

@@ -28,7 +28,7 @@ import (
 	"sync/atomic"
 	"time"
 
-	"github.com/panjf2000/ants/v2/internal"
+	syncx "github.com/panjf2000/ants/v2/internal/sync"
 )
 
 // Pool accepts the tasks from client, it limits the total of goroutines to a given number by recycling goroutines.
@@ -180,7 +180,7 @@ func NewPool(size int, options ...Option) (*Pool, error) {
 
 	p := &Pool{
 		capacity: int32(size),
-		lock:     internal.NewSpinLock(),
+		lock:     syncx.NewSpinLock(),
 		options:  opts,
 	}
 	p.workerCache.New = func() interface{} {

pool_func.go

@@ -28,7 +28,7 @@ import (
 	"sync/atomic"
 	"time"
 
-	"github.com/panjf2000/ants/v2/internal"
+	syncx "github.com/panjf2000/ants/v2/internal/sync"
 )
 
 // PoolWithFunc accepts the tasks from client,
@@ -208,7 +208,7 @@ func NewPoolWithFunc(size int, pf func(interface{}), options ...Option) (*PoolWi
 	p := &PoolWithFunc{
 		capacity: int32(size),
 		poolFunc: pf,
-		lock:     internal.NewSpinLock(),
+		lock:     syncx.NewSpinLock(),
 		options:  opts,
 	}
 	p.workerCache.New = func() interface{} {