initialize the pool patterns

concurrency/pool/main.go

@@ -0,0 +1,90 @@
+package main
+
+import (
+	"errors"
+	"io"
+	"log"
+	"sync"
+)
+
+// Pool manages a set of resources that can be shared safely by
+// multiply goroutines. The resource been 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 manage 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 uint32) (*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 free resources
+	case r, ok := <-p.resources:
+		if !ok {
+			return nil, ErrPoolClosed
+		}
+		log.Println("Aquire: ", "Shared Resource")
+		return r, nil
+	default:
+		log.Println("Aquire: ", "New Resource")
+		return p.factory()
+	}
+}
+
+// Release place a new resource into 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")
+	default:
+		// If the queue is already at capacity we close the resource
+		log.Println("Release:", "Closing")
+		r.Close()
+	}
+}
+
+// Close will shutdown the pool and close all existing resources.
+func (p *Pool) Close() {
+	// Secure this operation with release operation.
+	p.m.Lock()
+	defer p.m.Unlock()
+	// If the pool is already closed, do not 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
+	close(p.resources)
+	// Close the resources
+	for r := range p.resources {
+		r.Close()
+	}
+}