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resource_pool.go
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resource_pool.go
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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 provides functionality to manage and reuse resources
// like connections.
package pools
import (
"errors"
"fmt"
"time"
"github.com/youtube/vitess/go/sync2"
"golang.org/x/net/context"
)
var (
// ErrClosed is returned if ResourcePool is used when it's closed.
ErrClosed = errors.New("resource pool is closed")
// ErrTimeout is returned if a resource get times out.
ErrTimeout = errors.New("resource pool timed out")
)
// Factory is a function that can be used to create a resource.
type Factory func() (Resource, error)
// Resource defines the interface that every resource must provide.
// Thread synchronization between Close() and IsClosed()
// is the responsibility of the caller.
type Resource interface {
Close()
}
// ResourcePool allows you to use a pool of resources.
type ResourcePool struct {
resources chan resourceWrapper
factory Factory
capacity sync2.AtomicInt64
idleTimeout sync2.AtomicDuration
// stats
waitCount sync2.AtomicInt64
waitTime sync2.AtomicDuration
}
type resourceWrapper struct {
resource Resource
timeUsed time.Time
}
// NewResourcePool creates a new ResourcePool pool.
// capacity is the number of active resources in the pool:
// there can be up to 'capacity' of these at a given time.
// maxCap specifies the extent to which the pool can be resized
// in the future through the SetCapacity function.
// You cannot resize the pool beyond maxCap.
// If a resource is unused beyond idleTimeout, it's discarded.
// An idleTimeout of 0 means that there is no timeout.
func NewResourcePool(factory Factory, capacity, maxCap int, idleTimeout time.Duration) *ResourcePool {
if capacity <= 0 || maxCap <= 0 || capacity > maxCap {
panic(errors.New("invalid/out of range capacity"))
}
rp := &ResourcePool{
resources: make(chan resourceWrapper, maxCap),
factory: factory,
capacity: sync2.NewAtomicInt64(int64(capacity)),
idleTimeout: sync2.NewAtomicDuration(idleTimeout),
}
for i := 0; i < capacity; i++ {
rp.resources <- resourceWrapper{}
}
return rp
}
// Close empties the pool calling Close on all its resources.
// You can call Close while there are outstanding resources.
// It waits for all resources to be returned (Put).
// After a Close, Get is not allowed.
func (rp *ResourcePool) Close() {
_ = rp.SetCapacity(0)
}
// IsClosed returns true if the resource pool is closed.
func (rp *ResourcePool) IsClosed() (closed bool) {
return rp.capacity.Get() == 0
}
// Get will return the next available resource. If capacity
// has not been reached, it will create a new one using the factory. Otherwise,
// it will wait till the next resource becomes available or a timeout.
// A timeout of 0 is an indefinite wait.
func (rp *ResourcePool) Get(ctx context.Context) (resource Resource, err error) {
return rp.get(ctx, true)
}
func (rp *ResourcePool) get(ctx context.Context, wait bool) (resource Resource, err error) {
// If ctx has already expired, avoid racing with rp's resource channel.
select {
case <-ctx.Done():
return nil, ErrTimeout
default:
}
// Fetch
var wrapper resourceWrapper
var ok bool
select {
case wrapper, ok = <-rp.resources:
default:
if !wait {
return nil, nil
}
startTime := time.Now()
select {
case wrapper, ok = <-rp.resources:
case <-ctx.Done():
return nil, ErrTimeout
}
rp.recordWait(startTime)
}
if !ok {
return nil, ErrClosed
}
// Unwrap
idleTimeout := rp.idleTimeout.Get()
if wrapper.resource != nil && idleTimeout > 0 && wrapper.timeUsed.Add(idleTimeout).Sub(time.Now()) < 0 {
wrapper.resource.Close()
wrapper.resource = nil
}
if wrapper.resource == nil {
wrapper.resource, err = rp.factory()
if err != nil {
rp.resources <- resourceWrapper{}
}
}
return wrapper.resource, err
}
// Put will return a resource to the pool. For every successful Get,
// a corresponding Put is required. If you no longer need a resource,
// you will need to call Put(nil) instead of returning the closed resource.
// The will eventually cause a new resource to be created in its place.
func (rp *ResourcePool) Put(resource Resource) {
var wrapper resourceWrapper
if resource != nil {
wrapper = resourceWrapper{resource, time.Now()}
}
select {
case rp.resources <- wrapper:
default:
panic(errors.New("attempt to Put into a full ResourcePool"))
}
}
// SetCapacity changes the capacity of the pool.
// You can use it to shrink or expand, but not beyond
// the max capacity. If the change requires the pool
// to be shrunk, SetCapacity waits till the necessary
// number of resources are returned to the pool.
// A SetCapacity of 0 is equivalent to closing the ResourcePool.
func (rp *ResourcePool) SetCapacity(capacity int) error {
if capacity < 0 || capacity > cap(rp.resources) {
return fmt.Errorf("capacity %d is out of range", capacity)
}
// Atomically swap new capacity with old, but only
// if old capacity is non-zero.
var oldcap int
for {
oldcap = int(rp.capacity.Get())
if oldcap == 0 {
return ErrClosed
}
if oldcap == capacity {
return nil
}
if rp.capacity.CompareAndSwap(int64(oldcap), int64(capacity)) {
break
}
}
if capacity < oldcap {
for i := 0; i < oldcap-capacity; i++ {
wrapper := <-rp.resources
if wrapper.resource != nil {
wrapper.resource.Close()
}
}
} else {
for i := 0; i < capacity-oldcap; i++ {
rp.resources <- resourceWrapper{}
}
}
if capacity == 0 {
close(rp.resources)
}
return nil
}
func (rp *ResourcePool) recordWait(start time.Time) {
rp.waitCount.Add(1)
rp.waitTime.Add(time.Now().Sub(start))
}
// SetIdleTimeout sets the idle timeout.
func (rp *ResourcePool) SetIdleTimeout(idleTimeout time.Duration) {
rp.idleTimeout.Set(idleTimeout)
}
// StatsJSON returns the stats in JSON format.
func (rp *ResourcePool) StatsJSON() string {
c, a, mx, wc, wt, it := rp.Stats()
return fmt.Sprintf(`{"Capacity": %v, "Available": %v, "MaxCapacity": %v, "WaitCount": %v, "WaitTime": %v, "IdleTimeout": %v}`, c, a, mx, wc, int64(wt), int64(it))
}
// Stats returns the stats.
func (rp *ResourcePool) Stats() (capacity, available, maxCap, waitCount int64, waitTime, idleTimeout time.Duration) {
return rp.Capacity(), rp.Available(), rp.MaxCap(), rp.WaitCount(), rp.WaitTime(), rp.IdleTimeout()
}
// Capacity returns the capacity.
func (rp *ResourcePool) Capacity() int64 {
return rp.capacity.Get()
}
// Available returns the number of currently unused resources.
func (rp *ResourcePool) Available() int64 {
return int64(len(rp.resources))
}
// MaxCap returns the max capacity.
func (rp *ResourcePool) MaxCap() int64 {
return int64(cap(rp.resources))
}
// WaitCount returns the total number of waits.
func (rp *ResourcePool) WaitCount() int64 {
return rp.waitCount.Get()
}
// WaitTime returns the total wait time.
func (rp *ResourcePool) WaitTime() time.Duration {
return rp.waitTime.Get()
}
// IdleTimeout returns the idle timeout.
func (rp *ResourcePool) IdleTimeout() time.Duration {
return rp.idleTimeout.Get()
}