這次介紹最後一個建立型模式——物件池模式。顧名思義，物件池模式就是預先初始化建立好多個物件，並將之儲存在一個池子裡。當需要的時候，客戶端就可以從池子裡申請一個物件使用，使用完以後再將之放回到池子裡。池子裡的物件在應用執行期間永遠不會被破壞或回收。
適用場景：
- 當需要的物件的建立成本比較高，且該型別的物件在應用執行期間只需要有限的數量
- 物件是不可變的
- 效能原因：預建立的物件可以顯著提升應用效能
我們在開發中最熟悉的物件池應該是資料庫連線池了。因為網路因素，資料庫連線池中的每個物件的建立成本都比較高，且應用在執行期間會需要多個數據庫連線物件。另外，每個資料庫的連線池中物件的屬性都是一樣的，且在執行期間這些物件的屬性幾乎通常都是不可變的。
來看個模擬的資料庫連線物件池模型的例子。
iPoolObject.go
type iPoolObject interface {
//This is any id which can be used to compare two different pool objects
getID() string
}
connection.go
type connection struct {
id string
}
func (c *connection) getID() string {
return c.id
}
pool.go
import (
"fmt"
"sync"
) type pool struct {
idle []iPoolObject
active []iPoolObject
capacity int
muLock *sync.Mutex
} //initPool Initialize the pool
func initPool(poolObjects []iPoolObject) (*pool, error) {
if len(poolObjects) == 0 {
return nil, fmt.Errorf("cannot craete a pool of 0 length")
}
active := make([]iPoolObject, 0)
pool := &pool{
idle: poolObjects,
active: active,
capacity: len(poolObjects),
muLock: new(sync.Mutex),
}
return pool, nil
} func (p *pool) loan() (iPoolObject, error) {
p.muLock.Lock()
defer p.muLock.Unlock()
if len(p.idle) == 0 {
return nil, fmt.Errorf("no pool object free. Please request after sometime")
}
obj := p.idle[0]
p.idle = p.idle[1:]
p.active = append(p.active, obj)
fmt.Printf("Loan Pool Object with ID: %s\n", obj.getID())
return obj, nil
} func (p *pool) receive(target iPoolObject) error {
p.muLock.Lock()
defer p.muLock.Unlock()
err := p.remove(target)
if err != nil {
return err
}
p.idle = append(p.idle, target)
fmt.Printf("Return Pool Object with ID: %s\n", target.getID())
return nil
} func (p *pool) remove(target iPoolObject) error {
currentActiveLength := len(p.active)
for i, obj := range p.active {
if obj.getID() == target.getID() {
p.active[currentActiveLength-1], p.active[i] = p.active[i], p.active[currentActiveLength-1]
p.active = p.active[:currentActiveLength-1]
return nil
}
}
return fmt.Errorf("targe pool object doesn't belong to the pool")
}
main.go
import (
"log"
"strconv"
) func main() {
connections := make([]iPoolObject, 0)
for i := 0; i < 3; i++ {
c := &connection{id: strconv.Itoa(i)}
connections = append(connections, c)
}
pool, err := initPool(connections)
if err != nil {
log.Fatalf("Init Pool Error: %s", err)
}
conn1, err := pool.loan()
if err != nil {
log.Fatalf("Pool Loan Error: %s", err)
}
conn2, err := pool.loan()
if err != nil {
log.Fatalf("Pool Loan Error: %s", err)
}
_ = pool.receive(conn1)
_ = pool.receive(conn2)
}
輸出內容為：
Loan Pool Object with ID: 0
Loan Pool Object with ID: 1
Return Pool Object with ID: 0
Return Pool Object with ID: 1
程式碼已上傳至GitHub：zhyea / go-patterns / object-pool-pattern
END!