Define close resource not to return an error

There is nothing the pool can do on an error. If the client code
wishes to handle or log errors it can do so in the close resource
function.

This removes the need for background error reporting.

pool.go

@@ -21,12 +21,7 @@ const maxInt = int(maxUint >> 1)
 var ErrClosedPool = errors.New("cannot get from closed pool")
 
 type CreateFunc func(ctx context.Context) (res interface{}, err error)
-type CloseFunc func(res interface{}) (err error)
-
-// BackgroundErrorHandler is the type of function that handles background
-// errors. It may be called while the pool is locked. Therefore it must not call
-// any pool methods and should not perform any lengthy operations.
-type BackgroundErrorHandler func(err error)
+type CloseFunc func(res interface{})
 
 type resourceWrapper struct {
 	resource      interface{}
@@ -47,21 +42,19 @@ type Pool struct {
 	maxResourceCheckouts uint64
 	closed               bool
 
-	createRes              CreateFunc
-	closeRes               CloseFunc
-	backgroundErrorHandler BackgroundErrorHandler
+	createRes CreateFunc
+	closeRes  CloseFunc
 }
 
 func NewPool(createRes CreateFunc, closeRes CloseFunc) *Pool {
 	return &Pool{
-		cond:                   sync.NewCond(new(sync.Mutex)),
-		allResources:           make(map[interface{}]*resourceWrapper),
-		maxSize:                maxInt,
-		maxResourceDuration:    math.MaxInt64,
-		maxResourceCheckouts:   math.MaxUint64,
-		createRes:              createRes,
-		closeRes:               closeRes,
-		backgroundErrorHandler: func(error) {},
+		cond:                 sync.NewCond(new(sync.Mutex)),
+		allResources:         make(map[interface{}]*resourceWrapper),
+		maxSize:              maxInt,
+		maxResourceDuration:  math.MaxInt64,
+		maxResourceCheckouts: math.MaxUint64,
+		createRes:            createRes,
+		closeRes:             closeRes,
 	}
 }
 
@@ -72,10 +65,7 @@ func (p *Pool) Close() {
 	p.closed = true
 
 	for _, rw := range p.availableResources {
-		err := p.closeRes(rw.resource)
-		if err != nil {
-			p.backgroundErrorHandler(err)
-		}
+		p.closeRes(rw.resource)
 		delete(p.allResources, rw.resource)
 	}
 	p.availableResources = nil
@@ -166,17 +156,6 @@ func (p *Pool) SetMaxResourceCheckouts(n uint64) {
 	p.cond.L.Unlock()
 }
 
-// SetBackgroundErrorHandler assigns a handler for errors that have no other
-// place to be reported. For example, Get is called when no resources are
-// available. Get begins creating a new resource (in a goroutine). Before the
-// new resource is completed, the context passed to Get is canceled. Then the
-// new resource creation fails. f will be called with that error.
-func (p *Pool) SetBackgroundErrorHandler(f BackgroundErrorHandler) {
-	p.cond.L.Lock()
-	p.backgroundErrorHandler = f
-	p.cond.L.Unlock()
-}
-
 // Get gets a resource from the pool. If no resources are available and the pool
 // is not at maximum capacity it will create a new resource. If the pool is at
 // maximum capacity it will block until a resource is available. ctx can be used
@@ -258,17 +237,6 @@ func (p *Pool) Get(ctx context.Context) (interface{}, error) {
 	}
 }
 
-// func (p *Pool) backgroundReportError(errChan chan error) {
-// 	go func() {
-// 		err := <-errChan
-// 		if err != nil {
-// 			p.cond.L.Lock()
-// 			p.backgroundErrorHandler(err)
-// 			p.cond.L.Unlock()
-// 		}
-// 	}()
-// }
-
 // lockedAvailableGet gets the top resource from p.availableResources. p.cond.L
 // must already be locked. len(p.availableResources) must be > 0.
 func (p *Pool) lockedAvailableGet() interface{} {
@@ -284,10 +252,7 @@ func (p *Pool) lockedAvailableGet() interface{} {
 
 func (p *Pool) backgroundClose(res interface{}) {
 	go func() {
-		err := p.closeRes(res)
-		if err != nil {
-			p.backgroundErrorHandler(err)
-		}
+		p.closeRes(res)
 	}()
 }
 
@@ -347,11 +312,6 @@ func (p *Pool) Remove(res interface{}) {
 
 	// close the resource in the background
 	go func() {
-		err := p.closeRes(res)
-		if err != nil {
-			p.cond.L.Lock()
-			p.backgroundErrorHandler(err)
-			p.cond.L.Unlock()
-		}
+		p.closeRes(res)
 	}()
 }