Add initial implementation of priority queue, uses container/heap

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()
+	}
+}