Add Pool.AcquireAllIdle

pool.go

@@ -302,6 +302,23 @@ func (p *Pool) Acquire(ctx context.Context) (*Resource, error) {
 	}
 }
 
+// AcquireAllIdle atomically acquires all currently idle resources. Its intended
+// use is for health check and keep-alive functionality. It does not update pool
+// statistics.
+func (p *Pool) AcquireAllIdle() []*Resource {
+	p.cond.L.Lock()
+
+	for _, res := range p.idleResources {
+		res.status = resourceStatusAcquired
+	}
+	resources := make([]*Resource, len(p.idleResources))
+	copy(resources, p.idleResources)
+	p.idleResources = p.idleResources[0:0]
+
+	p.cond.L.Unlock()
+	return resources
+}
+
 // releaseAcquiredResource returns res to the the pool.
 func (p *Pool) releaseAcquiredResource(res *Resource) {
 	p.cond.L.Lock()

pool_test.go

@@ -197,6 +197,43 @@ func TestPoolAcquireContextCanceledDuringCreate(t *testing.T) {
 	assert.Nil(t, res)
 }
 
+func TestPoolAcquireAllIdle(t *testing.T) {
+	constructor, _ := createConstructor()
+	pool := puddle.NewPool(constructor, stubDestructor, 10)
+	defer pool.Close()
+
+	resources := make([]*puddle.Resource, 4)
+	var err error
+
+	resources[0], err = pool.Acquire(context.Background())
+	require.NoError(t, err)
+	resources[1], err = pool.Acquire(context.Background())
+	require.NoError(t, err)
+	resources[2], err = pool.Acquire(context.Background())
+	require.NoError(t, err)
+	resources[3], err = pool.Acquire(context.Background())
+	require.NoError(t, err)
+
+	assert.Len(t, pool.AcquireAllIdle(), 0)
+
+	resources[0].Release()
+	resources[3].Release()
+
+	assert.ElementsMatch(t, []*puddle.Resource{resources[0], resources[3]}, pool.AcquireAllIdle())
+
+	resources[0].Release()
+	resources[3].Release()
+	resources[1].Release()
+	resources[2].Release()
+
+	assert.ElementsMatch(t, resources, pool.AcquireAllIdle())
+
+	resources[0].Release()
+	resources[1].Release()
+	resources[2].Release()
+	resources[3].Release()
+}
+
 func TestPoolCloseClosesAllIdleResources(t *testing.T) {
 	constructor, _ := createConstructor()