Implement list, clear locks REST API w/ pkg/madmin support (#3491)

* Filter lock info based on bucket, prefix and time since lock was held
* Implement list and clear locks REST API
* madmin: Add list and clear locks API
* locks: Clear locks matching bucket, prefix, relTime.
* Gather lock information across nodes for both list and clear locks admin REST API.
* docs: Add lock API to management APIs

cmd/lockinfo-handlers_test.go

@@ -0,0 +1,81 @@
+/*
+ * Minio Cloud Storage, (C) 2016 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 cmd
+
+import (
+	"fmt"
+	"testing"
+	"time"
+)
+
+// TestListLocksInfo - Test for listLocksInfo.
+func TestListLocksInfo(t *testing.T) {
+	// Initialize globalNSMutex to validate listing of lock
+	// instrumentation information.
+	isDistXL := false
+	initNSLock(isDistXL)
+
+	// Acquire a few locks to populate lock instrumentation.
+	// Take 10 read locks on bucket1/prefix1/obj1
+	for i := 0; i < 10; i++ {
+		readLk := globalNSMutex.NewNSLock("bucket1", "prefix1/obj1")
+		readLk.RLock()
+	}
+
+	// Take write locks on bucket1/prefix/obj{11..19}
+	for i := 0; i < 10; i++ {
+		wrLk := globalNSMutex.NewNSLock("bucket1", fmt.Sprintf("prefix1/obj%d", 10+i))
+		wrLk.Lock()
+	}
+
+	testCases := []struct {
+		bucket   string
+		prefix   string
+		relTime  time.Duration
+		numLocks int
+	}{
+		// Test 1 - Matches all the locks acquired above.
+		{
+			bucket:   "bucket1",
+			prefix:   "prefix1",
+			relTime:  time.Duration(0 * time.Second),
+			numLocks: 20,
+		},
+		// Test 2 - Bucket doesn't match.
+		{
+			bucket:   "bucket",
+			prefix:   "prefix1",
+			relTime:  time.Duration(0 * time.Second),
+			numLocks: 0,
+		},
+		// Test 3 - Prefix doesn't match.
+		{
+			bucket:   "bucket1",
+			prefix:   "prefix11",
+			relTime:  time.Duration(0 * time.Second),
+			numLocks: 0,
+		},
+	}
+
+	for i, test := range testCases {
+		actual := listLocksInfo(test.bucket, test.prefix, test.relTime)
+		if len(actual) != test.numLocks {
+			t.Errorf("Test %d - Expected %d locks but observed %d locks",
+				i+1, test.numLocks, len(actual))
+		}
+	}
+}