SPVBlockStore: lock the store file as early as possible

core/src/main/java/org/bitcoinj/store/SPVBlockStore.java

@@ -119,6 +119,12 @@ public SPVBlockStore(NetworkParameters params, File file, int capacity, boolean
             boolean exists = file.exists();
             // Set up the backing file.
             randomAccessFile = new RandomAccessFile(file, "rw");
+            FileChannel channel = randomAccessFile.getChannel();
+            // Lock the file.
+            fileLock = channel.tryLock();
+            if (fileLock == null)
+                throw new ChainFileLockedException("Store file is already locked by another process");
+
             fileLength = getFileSize(capacity);
             if (!exists) {
                 log.info("Creating new SPV block chain file " + file);
@@ -140,11 +146,6 @@ else if (fileLength < randomAccessFile.length())
                 }
             }
 
-            FileChannel channel = randomAccessFile.getChannel();
-            fileLock = channel.tryLock();
-            if (fileLock == null)
-                throw new ChainFileLockedException("Store file is already locked by another process");
-
             // Map it into memory read/write. The kernel will take care of flushing writes to disk at the most
             // efficient times, which may mean that until the map is deallocated the data on disk is randomly
             // inconsistent. However the only process accessing it is us, via this mapping, so our own view will