Add port allocator and move ipset into orderedintset

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

collections/orderedintset.go

@@ -0,0 +1,89 @@
+package collections
+
+import (
+	"sort"
+	"sync"
+)
+
+// OrderedIntSet is a thread-safe sorted set and a stack.
+type OrderedIntSet struct {
+	sync.RWMutex
+	set []int
+}
+
+// NewOrderedSet returns an initialized OrderedSet
+func NewOrderedIntSet() *OrderedIntSet {
+	return &OrderedIntSet{}
+}
+
+// Push takes a string and adds it to the set. If the elem aready exists, it has no effect.
+func (s *OrderedIntSet) Push(elem int) {
+	s.RLock()
+	for _, e := range s.set {
+		if e == elem {
+			s.RUnlock()
+			return
+		}
+	}
+	s.RUnlock()
+
+	s.Lock()
+	s.set = append(s.set, elem)
+	// Make sure the list is always sorted
+	sort.Ints(s.set)
+	s.Unlock()
+}
+
+// Pop is an alias to PopFront()
+func (s *OrderedIntSet) Pop() int {
+	return s.PopFront()
+}
+
+// Pop returns the first elemen from the list and removes it.
+// If the list is empty, it returns 0
+func (s *OrderedIntSet) PopFront() int {
+	s.RLock()
+
+	for i, e := range s.set {
+		ret := e
+		s.RUnlock()
+		s.Lock()
+		s.set = append(s.set[:i], s.set[i+1:]...)
+		s.Unlock()
+		return ret
+	}
+	s.RUnlock()
+
+	return 0
+}
+
+// PullBack retrieve the last element of the list.
+// The element is not removed.
+// If the list is empty, an empty element is returned.
+func (s *OrderedIntSet) PullBack() int {
+	if len(s.set) == 0 {
+		return 0
+	}
+	return s.set[len(s.set)-1]
+}
+
+// Exists checks if the given element present in the list.
+func (s *OrderedIntSet) Exists(elem int) bool {
+	for _, e := range s.set {
+		if e == elem {
+			return true
+		}
+	}
+	return false
+}
+
+// Remove removes an element from the list.
+// If the element is not found, it has no effect.
+func (s *OrderedIntSet) Remove(elem int) {
+	for i, e := range s.set {
+		if e == elem {
+			s.set = append(s.set[:i], s.set[i+1:]...)
+			return
+		}
+	}
+}