conn_cache.go

package main

import (
	"fmt"
	"sync"
)

type Connection interface {
	Send([]byte) error
	Release()
}

type Cache interface {
	Acquire() (Connection, error)
	Release(Connection) error
}

type connection struct {
	sync.RWMutex
	cache *connectionCache // cache this connection belongs to
	conn  *int             // let's say it's FD
}

func (c *connection) Send(data []byte) error {
	c.RLock()
	defer c.RUnlock()
	if c.conn != nil {
		_ = data // send it
		return nil
	}
	return fmt.Errorf("connection has been closed")
}

func (c *connection) Release() {
	c.Lock()
	defer c.Unlock()
	_ = c.cache.Release(c)
	c.conn = nil
}

type connectionCache struct {
	sync.RWMutex
	available []*connection
	inUse     []*connection
}

func (cc *connectionCache) Acquire() (Connection, error) {
	cc.Lock()
	defer cc.Unlock()
	if len(cc.available) == 0 {
		return nil, fmt.Errorf("no available connection at this time")
	}
	conn := cc.available[len(cc.available)-1]
	cc.available = cc.available[:len(cc.available)-1]
	cc.inUse = append(cc.inUse, conn)
	return conn, nil
}

func (cc *connectionCache) Release(c Connection) error {
	cc.Lock()
	defer cc.Unlock()
	for i, inUse := range cc.inUse {
		if inUse == c {
			cc.available = append(cc.available, inUse)
			// https://github.com/golang/go/wiki/SliceTricks
			copy(cc.inUse[i:], cc.inUse[i+1:])
			cc.inUse[len(cc.inUse)-1] = nil
			cc.inUse = cc.inUse[:len(cc.inUse)-1]
			return nil
		}
	}
	return fmt.Errorf("Couldn't find connection in use")
}

func NewCache(initialSize int) Cache {
	c := &connectionCache{available: make([]*connection, initialSize), inUse: make([]*connection, 0)}
	for i := 0; i < initialSize; i++ {
		c.available[i] = &connection{cache: c, conn: &i}
	}
	return c
}

conn_cache_test.go

package main

import (
	"sync"
	"testing"
)

func TestCacheAcquireNormal(t *testing.T) {
	t.Parallel()
	size := 5
	cache := NewCache(size)
	connections := make([]Connection, size)
	for i := range connections {
		var err error
		connections[i], err = cache.Acquire()
		if err != nil {
			t.Error("expected no errors while acquiring the total number of connections")
		}
	}
}

func TestCacheAcquireNormalConcurrently(t *testing.T) {
	t.Parallel()
	size := 5
	cache := NewCache(size)
	var wg sync.WaitGroup
	wg.Add(size)
	for i := 0; i < size; i++ {
		go func() {
			conn, err := cache.Acquire()
			if conn == nil {
				t.Errorf("Connection shouldn't be nil")
			}
			if err != nil {
				t.Errorf("No error should be given but got %v", err)
			}
			wg.Done()
		}()
	}
	wg.Wait()
}

func TestCacheAcquireTooMany(t *testing.T) {
	t.Parallel()
	size := 5
	cache := NewCache(size)
	for i := 0; i < size; i++ {
		conn, err := cache.Acquire()
		if conn == nil {
			t.Errorf("Connection shouldn't be nil")
		}
		if err != nil {
			t.Errorf("No error should be given but got %v", err)
		}
	}
	conn, err := cache.Acquire()
	if conn != nil {
		t.Errorf("We should not have a connection")
	}
	if err == nil {
		t.Errorf("I was expecting an error because we're out of connections")
	}
}

func TestCacheAcquireAndReleaseNormal(t *testing.T) {
	t.Parallel()
	size := 5
	cache := NewCache(size)
	connections := make([]Connection, size)
	for i := range connections {
		var err error
		connections[i], err = cache.Acquire()
		if err != nil {
			t.Error("expected no errors while acquiring the total number of connections")
		}
	}
	for _, c := range connections {
		if err := c.Send([]byte{}); err != nil {
			t.Errorf("no send error expected by got %v", err)
		}
	}
	for _, c := range connections {
		c.Release()
	}
}

func TestCacheAcquireAndReleaseThenSend(t *testing.T) {
	t.Parallel()
	size := 1
	cache := NewCache(size)
	connections := make([]Connection, size)
	for i := range connections {
		var err error
		connections[i], err = cache.Acquire()
		if err != nil {
			t.Error("expected no errors while acquiring the total number of connections")
		}
	}
	for _, c := range connections {
		c.Release()
	}
	for _, c := range connections {
		if err := c.Send([]byte{}); err == nil {
			t.Errorf("send error expected")
		}
	}
}

func TestReleaseConnectionNotInCache(t *testing.T) {
	t.Parallel()
	size := 1
	cache := NewCache(size)
	connections := make([]Connection, size)
	for i := range connections {
		var err error
		connections[i], err = cache.Acquire()
		if err != nil {
			t.Error("expected no errors while acquiring the total number of connections")
		}
	}
	fakeConnection := &connection{}
	if err := cache.Release(fakeConnection); err == nil {
		t.Errorf("Should not be able to release a fake connection")
	}
}

func TestCacheAcquireSendAndReleaseConcurrently(t *testing.T) {
	t.Parallel()
	size := 10
	cache := NewCache(size)
	goroutines := 1000
	var wg sync.WaitGroup
	wg.Add(goroutines)
	for i := 0; i < goroutines; i++ {
		go func() {
			var conn Connection
			var err error
			if conn, err = cache.Acquire(); err == nil {
				conn.Send([]byte{})
				if releaseErr := cache.Release(conn); releaseErr != nil {
					t.Error("This connection should release successfully")
				}
			}
			wg.Done()
		}()
	}
	wg.Wait()
}

terminal.txt

time go test -cover -race -v .
=== RUN   TestCacheAcquireNormal
=== PAUSE TestCacheAcquireNormal
=== RUN   TestCacheAcquireNormalConcurrently
=== PAUSE TestCacheAcquireNormalConcurrently
=== RUN   TestCacheAcquireTooMany
=== PAUSE TestCacheAcquireTooMany
=== RUN   TestCacheAcquireAndReleaseNormal
=== PAUSE TestCacheAcquireAndReleaseNormal
=== RUN   TestCacheAcquireAndReleaseThenSend
=== PAUSE TestCacheAcquireAndReleaseThenSend
=== RUN   TestReleaseConnectionNotInCache
=== PAUSE TestReleaseConnectionNotInCache
=== RUN   TestCacheAcquireSendAndReleaseConcurrently
=== PAUSE TestCacheAcquireSendAndReleaseConcurrently
=== CONT  TestCacheAcquireNormal
=== CONT  TestCacheAcquireAndReleaseNormal
--- PASS: TestCacheAcquireNormal (0.00s)
=== CONT  TestCacheAcquireTooMany
--- PASS: TestCacheAcquireAndReleaseNormal (0.00s)
=== CONT  TestCacheAcquireAndReleaseThenSend
=== CONT  TestCacheAcquireNormalConcurrently
--- PASS: TestCacheAcquireAndReleaseThenSend (0.00s)
--- PASS: TestCacheAcquireTooMany (0.00s)
=== CONT  TestReleaseConnectionNotInCache
=== CONT  TestCacheAcquireSendAndReleaseConcurrently
--- PASS: TestReleaseConnectionNotInCache (0.00s)
--- PASS: TestCacheAcquireNormalConcurrently (0.00s)
--- PASS: TestCacheAcquireSendAndReleaseConcurrently (0.05s)
PASS
coverage: 100.0% of statements
ok  	_/Users/vaskozdravevski/tmp	1.096s

real	0m3.903s
user	0m5.955s
sys	0m1.280s