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pool.go
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pool.go
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// Copyright 2012 Gary Burd
//
// Licensed under the Apache License, Version 2.0 (the "License"): you may
// not use this file except in compliance with the License. You may obtain
// a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations
// under the License.
package redis
import (
"bytes"
"container/list"
"crypto/rand"
"crypto/sha1"
"errors"
"io"
"strconv"
"sync"
"time"
)
var nowFunc = time.Now // for testing
// ErrPoolExhausted is returned from a pool connection method (Do, Send,
// Receive, Flush, Err) when the maximum number of database connections in the
// pool has been reached.
var ErrPoolExhausted = errors.New("redigo: connection pool exhausted")
var errPoolClosed = errors.New("redigo: connection pool closed")
// Pool maintains a pool of connections. The application calls the Get method
// to get a connection from the pool and the connection's Close method to
// return the connection's resources to the pool.
//
// The following example shows how to use a pool in a web application. The
// application creates a pool at application startup and makes it available to
// request handlers using a global variable.
//
// func newPool(server, password string) *redis.Pool {
// return &redis.Pool{
// MaxIdle: 3,
// IdleTimeout: 240 * time.Second,
// Dial: func () (redis.Conn, error) {
// c, err := redis.Dial("tcp", server)
// if err != nil {
// return nil, err
// }
// if _, err := c.Do("AUTH", password); err != nil {
// c.Close()
// return nil, err
// }
// return c, err
// },
// TestOnBorrow: func(c redis.Conn, t time.Time) error {
// _, err := c.Do("PING")
// return err
// },
// }
// }
//
// var (
// pool *redis.Pool
// redisServer = flag.String("redisServer", ":6379", "")
// redisPassword = flag.String("redisPassword", "", "")
// )
//
// func main() {
// flag.Parse()
// pool = newPool(*redisServer, *redisPassword)
// ...
// }
//
// A request handler gets a connection from the pool and closes the connection
// when the handler is done:
//
// func serveHome(w http.ResponseWriter, r *http.Request) {
// conn := pool.Get()
// defer conn.Close()
// ....
// }
//
type Pool struct {
// Dial is an application supplied function for creating new connections.
Dial func() (Conn, error)
// TestOnBorrow is an optional application supplied function for checking
// the health of an idle connection before the connection is used again by
// the application. Argument t is the time that the connection was returned
// to the pool. If the function returns an error, then the connection is
// closed.
TestOnBorrow func(c Conn, t time.Time) error
// Maximum number of idle connections in the pool.
MaxIdle int
// Maximum number of connections allocated by the pool at a given time.
// When zero, there is no limit on the number of connections in the pool.
MaxActive int
// Close connections after remaining idle for this duration. If the value
// is zero, then idle connections are not closed. Applications should set
// the timeout to a value less than the server's timeout.
IdleTimeout time.Duration
// mu protects fields defined below.
mu sync.Mutex
closed bool
active int
// Stack of idleConn with most recently used at the front.
idle list.List
}
type idleConn struct {
c Conn
t time.Time
}
// NewPool is a convenience function for initializing a pool.
func NewPool(newFn func() (Conn, error), maxIdle int) *Pool {
return &Pool{Dial: newFn, MaxIdle: maxIdle}
}
// Get gets a connection. The application must close the returned connection.
// The connection acquires an underlying connection on the first call to the
// connection Do, Send, Receive, Flush or Err methods. An application can force
// the connection to acquire an underlying connection without executing a Redis
// command by calling the Err method.
func (p *Pool) Get() Conn {
return &pooledConnection{p: p}
}
// ActiveCount returns the number of active connections in the pool.
func (p *Pool) ActiveCount() int {
p.mu.Lock()
active := p.active
p.mu.Unlock()
return active
}
// Close releases the resources used by the pool.
func (p *Pool) Close() error {
p.mu.Lock()
idle := p.idle
p.idle.Init()
p.closed = true
p.active -= idle.Len()
p.mu.Unlock()
for e := idle.Front(); e != nil; e = e.Next() {
e.Value.(idleConn).c.Close()
}
return nil
}
// get prunes stale connections and returns a connection from the idle list or
// creates a new connection.
func (p *Pool) get() (Conn, error) {
p.mu.Lock()
if p.closed {
p.mu.Unlock()
return nil, errors.New("redigo: get on closed pool")
}
// Prune stale connections.
if timeout := p.IdleTimeout; timeout > 0 {
for i, n := 0, p.idle.Len(); i < n; i++ {
e := p.idle.Back()
if e == nil {
break
}
ic := e.Value.(idleConn)
if ic.t.Add(timeout).After(nowFunc()) {
break
}
p.idle.Remove(e)
p.active -= 1
p.mu.Unlock()
ic.c.Close()
p.mu.Lock()
}
}
// Get idle connection.
for i, n := 0, p.idle.Len(); i < n; i++ {
e := p.idle.Front()
if e == nil {
break
}
ic := e.Value.(idleConn)
p.idle.Remove(e)
test := p.TestOnBorrow
p.mu.Unlock()
if test == nil || test(ic.c, ic.t) == nil {
return ic.c, nil
}
ic.c.Close()
p.mu.Lock()
p.active -= 1
}
if p.MaxActive > 0 && p.active >= p.MaxActive {
p.mu.Unlock()
return nil, ErrPoolExhausted
}
// No idle connection, create new.
dial := p.Dial
p.active += 1
p.mu.Unlock()
c, err := dial()
if err != nil {
p.mu.Lock()
p.active -= 1
p.mu.Unlock()
c = nil
}
return c, err
}
func (p *Pool) put(c Conn, forceClose bool) error {
if c.Err() == nil && !forceClose {
p.mu.Lock()
if !p.closed {
p.idle.PushFront(idleConn{t: nowFunc(), c: c})
if p.idle.Len() > p.MaxIdle {
c = p.idle.Remove(p.idle.Back()).(idleConn).c
} else {
c = nil
}
}
p.mu.Unlock()
}
if c != nil {
p.mu.Lock()
p.active -= 1
p.mu.Unlock()
return c.Close()
}
return nil
}
type pooledConnection struct {
c Conn
err error
p *Pool
state int
}
func (c *pooledConnection) get() error {
if c.err == nil && c.c == nil {
c.c, c.err = c.p.get()
}
return c.err
}
var (
sentinel []byte
sentinelOnce sync.Once
)
func initSentinel() {
p := make([]byte, 64)
if _, err := rand.Read(p); err == nil {
sentinel = p
} else {
h := sha1.New()
io.WriteString(h, "Oops, rand failed. Use time instead.")
io.WriteString(h, strconv.FormatInt(time.Now().UnixNano(), 10))
sentinel = h.Sum(nil)
}
}
func (c *pooledConnection) Close() (err error) {
if c.c != nil {
if c.state&multiState != 0 {
c.c.Send("DISCARD")
c.state &^= (multiState | watchState)
} else if c.state&watchState != 0 {
c.c.Send("UNWATCH")
c.state &^= watchState
}
if c.state&subscribeState != 0 {
c.c.Send("UNSUBSCRIBE")
c.c.Send("PUNSUBSCRIBE")
// To detect the end of the message stream, ask the server to echo
// a sentinel value and read until we see that value.
sentinelOnce.Do(initSentinel)
c.c.Send("ECHO", sentinel)
c.c.Flush()
for {
p, err := c.c.Receive()
if err != nil {
break
}
if p, ok := p.([]byte); ok && bytes.Equal(p, sentinel) {
c.state &^= subscribeState
break
}
}
}
c.c.Do("")
c.p.put(c.c, c.state != 0)
c.c = nil
c.err = errPoolClosed
}
return err
}
func (c *pooledConnection) Err() error {
if err := c.get(); err != nil {
return err
}
return c.c.Err()
}
func (c *pooledConnection) Do(commandName string, args ...interface{}) (reply interface{}, err error) {
if err := c.get(); err != nil {
return nil, err
}
ci := lookupCommandInfo(commandName)
c.state = (c.state | ci.set) &^ ci.clear
return c.c.Do(commandName, args...)
}
func (c *pooledConnection) Send(commandName string, args ...interface{}) error {
if err := c.get(); err != nil {
return err
}
ci := lookupCommandInfo(commandName)
c.state = (c.state | ci.set) &^ ci.clear
return c.c.Send(commandName, args...)
}
func (c *pooledConnection) Flush() error {
if err := c.get(); err != nil {
return err
}
return c.c.Flush()
}
func (c *pooledConnection) Receive() (reply interface{}, err error) {
if err := c.get(); err != nil {
return nil, err
}
return c.c.Receive()
}