Add Guard and rename variable

wvlet-log/src/main/scala/wvlet/log/Guard.scala

@@ -0,0 +1,34 @@
+/*
+ * 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 wvlet.log
+
+import java.util.concurrent.locks.ReentrantLock
+
+/**
+  *
+  */
+trait Guard {
+  private[this] val lock = new ReentrantLock()
+  protected def newCondition = lock.newCondition()
+
+  def guard[U](body: => U) : U = {
+    lock.lockInterruptibly()
+    try {
+      body
+    }
+    finally {
+      lock.unlock()
+    }
+  }
+}

wvlet-log/src/main/scala/wvlet/log/LogLevelScanner.scala

@@ -122,24 +122,23 @@ private[log] class LogLevelScanner extends Guard {
     state.set(STOPPING)
   }
 
-  private var lastCheckedMillis: Option[Long] = None
+  private var lastScheduledMillis: Option[Long] = None
   private var lastScannedMillis: Option[Long] = None
 
   private def run {
     while (state.get() != STOPPING) {
       // Periodically run
       val currentTimeMillis = System.currentTimeMillis()
       val scanIntervalMillis = getConfig.scanInterval.toMillis
-      if (lastCheckedMillis.isEmpty || currentTimeMillis - lastCheckedMillis.get > scanIntervalMillis) {
+      if (lastScheduledMillis.isEmpty || currentTimeMillis - lastScheduledMillis.get > scanIntervalMillis) {
         val updatedLastScannedMillis = scan(getConfig.logLevelFileCandidates, lastScannedMillis)
         guard {
           lastScannedMillis = updatedLastScannedMillis
         }
-        lastCheckedMillis = Some(currentTimeMillis)
+        lastScheduledMillis = Some(currentTimeMillis)
       }
-      // wait
-      val sleepTime = scanIntervalMillis - math.max(0, math.min(scanIntervalMillis, currentTimeMillis - lastCheckedMillis.get))
-
+      // wait until next scheduled time
+      val sleepTime = scanIntervalMillis - math.max(0, math.min(scanIntervalMillis, currentTimeMillis - lastScheduledMillis.get))
       guard {
         if (configChanged.await(sleepTime, TimeUnit.MILLISECONDS)) {
           // awaken due to config change