The variable DLedgerMmapFileStore#isDiskFull should be decorated with…

… the volatile. (#104)

* [ISSUE #103] fix: The variable DLedgerMmapFileStore#isDiskFull should be decorated with the volatile

* fix: Avoid double counting elapsed time.

src/main/java/io/openmessaging/storage/dledger/store/file/DLedgerMmapFileStore.java

@@ -60,7 +60,7 @@ public class DLedgerMmapFileStore extends DLedgerStore {
     private ThreadLocal<ByteBuffer> localIndexBuffer;
     private FlushDataService flushDataService;
     private CleanSpaceService cleanSpaceService;
-    private boolean isDiskFull = false;
+    private volatile boolean isDiskFull = false;
 
     private long lastCheckPointTimeMs = System.currentTimeMillis();
 
@@ -632,8 +632,9 @@ public FlushDataService(String name, Logger logger) {
                 long start = System.currentTimeMillis();
                 DLedgerMmapFileStore.this.dataFileList.flush(0);
                 DLedgerMmapFileStore.this.indexFileList.flush(0);
-                if (DLedgerUtils.elapsed(start) > 500) {
-                    logger.info("Flush data cost={} ms", DLedgerUtils.elapsed(start));
+                long elapsed;
+                if ((elapsed = DLedgerUtils.elapsed(start)) > 500) {
+                    logger.info("Flush data cost={} ms", elapsed);
                 }
 
                 if (DLedgerUtils.elapsed(lastCheckPointTimeMs) > dLedgerConfig.getCheckPointInterval()) {