这次介绍最后一个创建型模式——对象池模式。顾名思义，对象池模式就是预先初始化创建好多个对象，并将之保存在一个池子里。当需要的时候，客户端就可以从池子里申请一个对象使用，使用完以后再将之放回到池子里。池子里的对象在应用运行期间永远不会被破坏或回收。
适用场景：
我们在开发中最熟悉的对象池应该是数据库连接池了。因为网络因素，数据库连接池中的每个对象的创建成本都比较高，且应用在运行期间会需要多个数据库连接对象。另外，每个数据库的连接池中对象的属性都是一样的，且在运行期间这些对象的属性几乎通常都是不可变的。
来看个模拟的数据库连接对象池模型的例子。
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)
}
输出内容为：
Loan Pool Object with ID: 0 Loan Pool Object with ID: 1 Return Pool Object with ID: 0 Return Pool Object with ID: 1
代码已上传至GitHub：zhyea / go-patterns / object-pool-pattern
END!
原文：https://www.cnblogs.com/amunote/p/15259628.html