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// Copyright 2012, Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package pools
import (
"fmt"
"sync"
"time"
)
// RoundRobin is deprecated. Use ResourcePool instead.
// RoundRobin allows you to use a pool of resources in a round robin fashion.
type RoundRobin struct {
mu sync.Mutex
available *sync.Cond
resources chan fifoWrapper
size int64
factory Factory
idleTimeout time.Duration
// stats
waitCount int64
waitTime time.Duration
}
type fifoWrapper struct {
resource Resource
timeUsed time.Time
}
// NewRoundRobin creates a new RoundRobin pool.
// capacity is the maximum number of resources RoundRobin will create.
// factory will be the function used to create resources.
// If a resource is unused beyond idleTimeout, it's discarded.
func NewRoundRobin(capacity int, idleTimeout time.Duration) *RoundRobin {
r := &RoundRobin{
resources: make(chan fifoWrapper, capacity),
size: 0,
idleTimeout: idleTimeout,
}
r.available = sync.NewCond(&r.mu)
return r
}
// Open starts allowing the creation of resources
func (rr *RoundRobin) Open(factory Factory) {
rr.mu.Lock()
defer rr.mu.Unlock()
rr.factory = factory
}
// Close empties the pool calling Close on all its resources.
// It waits for all resources to be returned (Put).
func (rr *RoundRobin) Close() {
rr.mu.Lock()
defer rr.mu.Unlock()
for rr.size > 0 {
select {
case fw := <-rr.resources:
go fw.resource.Close()
rr.size--
default:
rr.available.Wait()
}
}
rr.factory = nil
}
func (rr *RoundRobin) IsClosed() bool {
return rr.factory == nil
}
// Get will return the next available resource. If none is available, and capacity
// has not been reached, it will create a new one using the factory. Otherwise,
// it will indefinitely wait till the next resource becomes available.
func (rr *RoundRobin) Get() (resource Resource, err error) {
return rr.get(true)
}
// TryGet will return the next available resource. If none is available, and capacity
// has not been reached, it will create a new one using the factory. Otherwise,
// it will return nil with no error.
func (rr *RoundRobin) TryGet() (resource Resource, err error) {
return rr.get(false)
}
func (rr *RoundRobin) get(wait bool) (resource Resource, err error) {
rr.mu.Lock()
defer rr.mu.Unlock()
// Any waits in this loop will release the lock, and it will be
// reacquired before the waits return.
for {
select {
case fw := <-rr.resources:
// Found a free resource in the channel
if rr.idleTimeout > 0 && fw.timeUsed.Add(rr.idleTimeout).Sub(time.Now()) < 0 {
// resource has been idle for too long. Discard & go for next.
go fw.resource.Close()
rr.size--
// Nobody else should be waiting, but signal anyway.
rr.available.Signal()
continue
}
return fw.resource, nil
default:
// resource channel is empty
if rr.size >= int64(cap(rr.resources)) {
// The pool is full
if wait {
start := time.Now()
rr.available.Wait()
rr.recordWait(start)
continue
}
return nil, nil
}
// Pool is not full. Create a resource.
if resource, err = rr.waitForCreate(); err != nil {
// size was decremented, and somebody could be waiting.
rr.available.Signal()
return nil, err
}
// Creation successful. Account for this by incrementing size.
rr.size++
return resource, err
}
}
panic("unreachable")
}
func (rr *RoundRobin) recordWait(start time.Time) {
rr.waitCount++
rr.waitTime += time.Now().Sub(start)
}
func (rr *RoundRobin) waitForCreate() (resource Resource, err error) {
// Prevent thundering herd: increment size before creating resource, and decrement after.
rr.size++
rr.mu.Unlock()
defer func() {
rr.mu.Lock()
rr.size--
}()
return rr.factory()
}
// Put will return a resource to the pool. You MUST return every resource to the pool,
// even if it's closed. If a resource is closed, you should call Put(nil).
func (rr *RoundRobin) Put(resource Resource) {
rr.mu.Lock()
defer rr.available.Signal()
defer rr.mu.Unlock()
if rr.size > int64(cap(rr.resources)) {
if resource != nil {
go resource.Close()
}
rr.size--
} else if resource == nil {
rr.size--
} else {
if len(rr.resources) == cap(rr.resources) {
panic("unexpected")
}
rr.resources <- fifoWrapper{resource, time.Now()}
}
}
// Set capacity changes the capacity of the pool.
// You can use it to expand or shrink.
func (rr *RoundRobin) SetCapacity(capacity int) error {
rr.mu.Lock()
defer rr.available.Broadcast()
defer rr.mu.Unlock()
nr := make(chan fifoWrapper, capacity)
// This loop transfers resources from the old channel
// to the new one, until it fills up or runs out.
// It discards extras, if any.
for {
select {
case fw := <-rr.resources:
if len(nr) < cap(nr) {
nr <- fw
} else {
go fw.resource.Close()
rr.size--
}
continue
default:
}
break
}
rr.resources = nr
return nil
}
func (rr *RoundRobin) SetIdleTimeout(idleTimeout time.Duration) {
rr.mu.Lock()
defer rr.mu.Unlock()
rr.idleTimeout = idleTimeout
}
func (rr *RoundRobin) StatsJSON() string {
s, c, a, wc, wt, it := rr.Stats()
return fmt.Sprintf("{\"Size\": %v, \"Capacity\": %v, \"Available\": %v, \"WaitCount\": %v, \"WaitTime\": %v, \"IdleTimeout\": %v}", s, c, a, wc, int64(wt), int64(it))
}
func (rr *RoundRobin) Stats() (size, capacity, available, waitCount int64, waitTime, idleTimeout time.Duration) {
rr.mu.Lock()
defer rr.mu.Unlock()
return rr.size, int64(cap(rr.resources)), int64(len(rr.resources)), rr.waitCount, rr.waitTime, rr.idleTimeout
}