pool.md

pool

go标准库sync.pool

{% embed url="https://golang.org/src/sync/pool.go" %}

动手实现

import (
	"errors"
	"io"
	"log"
	"sync"
)

// Pool manages a set of resources that can be shared safely by
// multiple goroutines. The resource being managed must implement
// the io.Closer interface.
type Pool struct {
	m         sync.Mutex
	resources chan io.Closer
	factory   func() (io.Closer, error)
	closed    bool
}

// ErrPoolClosed is returned when an Acquire returns on a
// closed pool.
var ErrPoolClosed = errors.New("Pool has been closed.")

// New creates a pool that manages resources. A pool requires a
// function that can allocate a new resource and the size of
// the pool.
func New(fn func() (io.Closer, error), size uint) (*Pool, error) {
	if size <= 0 {
		return nil, errors.New("Size value too small.")
	}

	return &Pool{
		factory:   fn,
		resources: make(chan io.Closer, size),
	}, nil
}

// Acquire retrieves a resource	from the pool.
func (p *Pool) Acquire() (io.Closer, error) {
	select {
	// Check for a free resource.
	case r, ok := <-p.resources:
		log.Println("Acquire:", "Shared Resource")
		if !ok {
			return nil, ErrPoolClosed
		}
		return r, nil

	// Provide a new resource since there are none available.
	default:
		log.Println("Acquire:", "New Resource")
		return p.factory()
	}
}

// Release places a new resource onto the pool.
func (p *Pool) Release(r io.Closer) {
	// Secure this operation with the Close operation.
	p.m.Lock()
	defer p.m.Unlock()

	// If the pool is closed, discard the resource.
	if p.closed {
		r.Close()
		return
	}

	select {
	// Attempt to place the new resource on the queue.
	case p.resources <- r:
		log.Println("Release:", "In Queue")

	// If the queue is already at cap we close the resource.
	default:
		log.Println("Release:", "Closing")
		r.Close()
	}
}

// Close will shutdown the pool and close all existing resources.
func (p *Pool) Close() {
	// Secure this operation with the Release operation.
	p.m.Lock()
	defer p.m.Unlock()

	// If the pool is already close, don't do anything.
	if p.closed {
		return
	}

	// Set the pool as closed.
	p.closed = true

	// Close the channel before we drain the channel of its
	// resources. If we don't do this, we will have a deadlock.
	close(p.resources)

	// Close the resources
	for r := range p.resources {
		r.Close()
	}
}

main程序

import (
	"gobasis/src/GoInAction/pool"
	"io"
	"log"
	"math/rand"
	"sync"
	"sync/atomic"
	"time"
)

const (
	maxGoroutines   = 25 // the number of routines to use.
	pooledResources = 2  // number of resources in the pool
)

// dbConnection simulates a resource to share.
type dbConnection struct {
	ID int32
}

// Close implements the io.Closer interface so dbConnection
// can be managed by the pool. Close performs any resource
// release management.
func (dbConn *dbConnection) Close() error {
	log.Println("Close: Connection", dbConn.ID)
	return nil
}

// idCounter provides support for giving each connection a unique id.
var idCounter int32

// createConnection is a factory method that will be called by
// the pool when a new connection is needed.
func createConnection() (io.Closer, error) {
	id := atomic.AddInt32(&idCounter, 1)
	log.Println("Create: New Connection", id)

	return &dbConnection{id}, nil
}

// main is the entry point for all Go programs.
func main() {
	var wg sync.WaitGroup
	wg.Add(maxGoroutines)

	// Create the pool to manage our connections.
	p, err := pool.New(createConnection, pooledResources)
	if err != nil {
		log.Println(err)
	}

	// Perform queries using connections from the pool.
	for query := 0; query < maxGoroutines; query++ {
		// Each goroutine needs its own copy of the query
		// value else they will all be sharing the same query
		// variable.
		go func(q int) {
			performQueries(q, p)
			wg.Done()
		}(query)
	}

	// Wait for the goroutines to finish.
	wg.Wait()

	// Close the pool.
	log.Println("Shutdown Program.")
	p.Close()
}

// performQueries tests the resource pool of connections.
func performQueries(query int, p *pool.Pool) {
	// Acquire a connection from the pool.
	conn, err := p.Acquire()
	if err != nil {
		log.Println(err)
		return
	}

	// Release the connection back to the pool.
	defer p.Release(conn)

	// Wait to simulate a query response.
	time.Sleep(time.Duration(rand.Intn(1000)) * time.Millisecond)
	log.Printf("Query: QID[%d] CID[%d]\n", query, conn.(*dbConnection).ID)
}