add priority queue

examples/pq/main.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"fmt"
+
+	pq "github.com/sunvim/utils/priorityqueue"
+)
+
+func main() {
+	q := pq.NewPriorityQueue(5, false)
+
+	q.Put(&Node{Number: 5, Name: "hello"})
+	q.Put(&Node{Number: 3, Name: "world"})
+	q.Put(&Node{Number: 4, Name: "sky"})
+	q.Put(&Node{Number: 1, Name: "mobus"})
+	q.Put(&Node{Number: 2, Name: "sunqc"})
+
+	for i := 0; i < 5; i++ {
+		v, _ := q.Get(i)
+		fmt.Printf("item: %+v \n", v)
+	}
+
+}
+
+type Node struct {
+	Number uint64
+	Name   string
+}
+
+func (n *Node) Compare(other pq.Item) int {
+	o := other.(*Node)
+	if o.Number > n.Number {
+		return 1
+	} else if o.Number == n.Number {
+		return 0
+	}
+	return -1
+}

priorityqueue/error.go

@@ -0,0 +1,16 @@
+package priorityqueue
+
+import "errors"
+
+var (
+	// ErrDisposed is returned when an operation is performed on a disposed
+	// queue.
+	ErrDisposed = errors.New(`queue: disposed`)
+
+	// ErrTimeout is returned when an applicable queue operation times out.
+	ErrTimeout = errors.New(`queue: poll timed out`)
+
+	// ErrEmptyQueue is returned when an non-applicable queue operation was called
+	// due to the queue's empty item state
+	ErrEmptyQueue = errors.New(`queue: empty queue`)
+)

priorityqueue/pq.go

@@ -0,0 +1,242 @@
+package priorityqueue
+
+import "sync"
+
+// Item is an item that can be added to the priority queue.
+type Item interface {
+	// Compare returns a bool that can be used to determine
+	// ordering in the priority queue.  Assuming the queue
+	// is in ascending order, this should return > logic.
+	// Return 1 to indicate this object is greater than the
+	// the other logic, 0 to indicate equality, and -1 to indicate
+	// less than other.
+	Compare(other Item) int
+}
+
+type priorityItems []Item
+
+func (items *priorityItems) swap(i, j int) {
+	(*items)[i], (*items)[j] = (*items)[j], (*items)[i]
+}
+
+func (items *priorityItems) pop() Item {
+	size := len(*items)
+
+	// Move last leaf to root, and 'pop' the last item.
+	items.swap(size-1, 0)
+	item := (*items)[size-1] // Item to return.
+	(*items)[size-1], *items = nil, (*items)[:size-1]
+
+	// 'Bubble down' to restore heap property.
+	index := 0
+	childL, childR := 2*index+1, 2*index+2
+	for len(*items) > childL {
+		child := childL
+		if len(*items) > childR && (*items)[childR].Compare((*items)[childL]) < 0 {
+			child = childR
+		}
+
+		if (*items)[child].Compare((*items)[index]) < 0 {
+			items.swap(index, child)
+
+			index = child
+			childL, childR = 2*index+1, 2*index+2
+		} else {
+			break
+		}
+	}
+
+	return item
+}
+
+func (items *priorityItems) get(number int) []Item {
+	returnItems := make([]Item, 0, number)
+	for i := 0; i < number; i++ {
+		if len(*items) == 0 {
+			break
+		}
+
+		returnItems = append(returnItems, items.pop())
+	}
+
+	return returnItems
+}
+
+func (items *priorityItems) push(item Item) {
+	// Stick the item as the end of the last level.
+	*items = append(*items, item)
+
+	// 'Bubble up' to restore heap property.
+	index := len(*items) - 1
+	parent := int((index - 1) / 2)
+	for parent >= 0 && (*items)[parent].Compare(item) > 0 {
+		items.swap(index, parent)
+
+		index = parent
+		parent = int((index - 1) / 2)
+	}
+}
+
+// PriorityQueue is similar to queue except that it takes
+// items that implement the Item interface and adds them
+// to the queue in priority order.
+type PriorityQueue struct {
+	waiters         waiters
+	items           priorityItems
+	itemMap         map[Item]struct{}
+	lock            sync.Mutex
+	disposeLock     sync.Mutex
+	disposed        bool
+	allowDuplicates bool
+}
+
+// Put adds items to the queue.
+func (pq *PriorityQueue) Put(items ...Item) error {
+	if len(items) == 0 {
+		return nil
+	}
+
+	pq.lock.Lock()
+	defer pq.lock.Unlock()
+
+	if pq.disposed {
+		return ErrDisposed
+	}
+
+	for _, item := range items {
+		if pq.allowDuplicates {
+			pq.items.push(item)
+		} else if _, ok := pq.itemMap[item]; !ok {
+			pq.itemMap[item] = struct{}{}
+			pq.items.push(item)
+		}
+	}
+
+	for {
+		sema := pq.waiters.get()
+		if sema == nil {
+			break
+		}
+
+		sema.response.Add(1)
+		sema.ready <- true
+		sema.response.Wait()
+		if len(pq.items) == 0 {
+			break
+		}
+	}
+
+	return nil
+}
+
+// Get retrieves items from the queue.  If the queue is empty,
+// this call blocks until the next item is added to the queue.  This
+// will attempt to retrieve number of items.
+func (pq *PriorityQueue) Get(number int) ([]Item, error) {
+	if number < 1 {
+		return nil, nil
+	}
+
+	pq.lock.Lock()
+
+	if pq.disposed {
+		pq.lock.Unlock()
+		return nil, ErrDisposed
+	}
+
+	var items []Item
+
+	// Remove references to popped items.
+	deleteItems := func(items []Item) {
+		for _, item := range items {
+			delete(pq.itemMap, item)
+		}
+	}
+
+	if len(pq.items) == 0 {
+		sema := newSema()
+		pq.waiters.put(sema)
+		pq.lock.Unlock()
+
+		<-sema.ready
+
+		if pq.Disposed() {
+			return nil, ErrDisposed
+		}
+
+		items = pq.items.get(number)
+		if !pq.allowDuplicates {
+			deleteItems(items)
+		}
+		sema.response.Done()
+		return items, nil
+	}
+
+	items = pq.items.get(number)
+	deleteItems(items)
+	pq.lock.Unlock()
+	return items, nil
+}
+
+// Peek will look at the next item without removing it from the queue.
+func (pq *PriorityQueue) Peek() Item {
+	pq.lock.Lock()
+	defer pq.lock.Unlock()
+	if len(pq.items) > 0 {
+		return pq.items[0]
+	}
+	return nil
+}
+
+// Empty returns a bool indicating if there are any items left
+// in the queue.
+func (pq *PriorityQueue) Empty() bool {
+	pq.lock.Lock()
+	defer pq.lock.Unlock()
+
+	return len(pq.items) == 0
+}
+
+// Len returns a number indicating how many items are in the queue.
+func (pq *PriorityQueue) Len() int {
+	pq.lock.Lock()
+	defer pq.lock.Unlock()
+
+	return len(pq.items)
+}
+
+// Disposed returns a bool indicating if this queue has been disposed.
+func (pq *PriorityQueue) Disposed() bool {
+	pq.disposeLock.Lock()
+	defer pq.disposeLock.Unlock()
+
+	return pq.disposed
+}
+
+// Dispose will prevent any further reads/writes to this queue
+// and frees available resources.
+func (pq *PriorityQueue) Dispose() {
+	pq.lock.Lock()
+	defer pq.lock.Unlock()
+
+	pq.disposeLock.Lock()
+	defer pq.disposeLock.Unlock()
+
+	pq.disposed = true
+	for _, waiter := range pq.waiters {
+		waiter.response.Add(1)
+		waiter.ready <- true
+	}
+
+	pq.items = nil
+	pq.waiters = nil
+}
+
+// NewPriorityQueue is the constructor for a priority queue.
+func NewPriorityQueue(hint int, allowDuplicates bool) *PriorityQueue {
+	return &PriorityQueue{
+		items:           make(priorityItems, 0, hint),
+		itemMap:         make(map[Item]struct{}, hint),
+		allowDuplicates: allowDuplicates,
+	}
+}