Add initial implementation of priority queue, uses container/heap

pkg/storage/pq/pq.go

@@ -0,0 +1,70 @@
+/*
+ * Minimalist Object Storage, (C) 2015 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package pq
+
+import "container/heap"
+
+// Item container for tasks in priority queue
+type Item struct {
+	task Task // task
+
+	// The index is needed by Fix and is maintained by the heap.Interface methods.
+	index int // The index of the item in the heap.
+}
+
+// A PriorityQueue implements heap.Interface and holds Items.
+type PriorityQueue []*Item
+
+// Len length of current priority queue
+func (pq PriorityQueue) Len() int { return len(pq) }
+
+// Less used internally by heap.Interface to arrange items in order
+func (pq PriorityQueue) Less(i, j int) bool {
+	// We want Pop to give us the highest, not lowest, priority so we use greater than here.
+	return pq[i].task.GetPriority() > pq[j].task.GetPriority()
+}
+
+// Swap used internally by heap.Interface to arrange incoming items
+func (pq PriorityQueue) Swap(i, j int) {
+	pq[i], pq[j] = pq[j], pq[i]
+	pq[i].index = i
+	pq[j].index = j
+}
+
+// Push push items onto priority queue
+func (pq *PriorityQueue) Push(x interface{}) {
+	n := len(*pq)
+	item := x.(*Item)
+	item.index = n
+	*pq = append(*pq, item)
+}
+
+// Pop pop items with highest priority
+func (pq *PriorityQueue) Pop() interface{} {
+	old := *pq
+	n := len(old)
+	item := old[n-1]
+	item.index = -1 // for safety
+	*pq = old[0 : n-1]
+	return item
+}
+
+// Fix modifies an item in-place on the queue
+func (pq *PriorityQueue) Fix(item *Item, task Task) {
+	item.task = task
+	heap.Fix(pq, item.index)
+}

pkg/storage/pq/pq_test.go

@@ -0,0 +1,81 @@
+/*
+ * Minimalist Object Storage, (C) 2015 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package pq
+
+import (
+	"container/heap"
+	"fmt"
+	"testing"
+
+	. "github.com/minio/check"
+)
+
+func Test(t *testing.T) { TestingT(t) }
+
+type MySuite struct{}
+
+var _ = Suite(&MySuite{})
+
+func helloTask1() error {
+	fmt.Println("Hello task1")
+	return nil
+}
+
+func helloTask2() error {
+	fmt.Println("Hello task2")
+	return nil
+}
+
+func newJob1() error {
+	fmt.Println("New Job1")
+	return nil
+}
+
+func newJob2() error {
+	fmt.Println("New Job2")
+	return nil
+}
+
+func (s *MySuite) TestPQ(c *C) {
+	// Create a priority queue, put the items in it, and
+	// establish the priority queue (heap) invariants.
+	pq := make(PriorityQueue, 2)
+	pq[0] = &Item{
+		task:  Task{job: helloTask1, priority: 2},
+		index: 0,
+	}
+	pq[1] = &Item{
+		task:  Task{job: helloTask2, priority: 1},
+		index: 1,
+	}
+	heap.Init(&pq)
+
+	// Insert a new item and then modify its priority.
+	item := &Item{
+		task: Task{job: newJob1, priority: 5},
+	}
+	heap.Push(&pq, item)
+	newTask := Task{job: newJob2, priority: 6}
+	pq.Fix(item, newTask)
+
+	// Take the items out; they arrive in decreasing priority order.
+	for pq.Len() > 0 {
+		item := heap.Pop(&pq).(*Item)
+		fmt.Printf("%.2d", item.task.GetPriority())
+		item.task.Execute()
+	}
+}

pkg/storage/pq/task.go

@@ -0,0 +1,38 @@
+/*
+ * Minimalist Object Storage, (C) 2015 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package pq
+
+// Task container for any generic tasks
+type Task struct {
+	job      func() error
+	priority int
+}
+
+// GetPriority get current task priority
+func (t Task) GetPriority() int {
+	return t.priority
+}
+
+// UpdatePriority update current task priority
+func (t Task) UpdatePriority(p int) {
+	t.priority = p
+}
+
+// Execute execute current task
+func (t Task) Execute() error {
+	return t.job()
+}