Fixed overlapping file lock exception

- Updated SynchronizedFileStream class
- Updated CachedMapsFile#load() method

Author: josemmo

src/main/java/io/josemmo/bukkit/plugin/storage/CachedMapsFile.java

@@ -114,6 +114,7 @@ public int getDelay() {
     private void load() {
         // Try to load maps from disk
         if (exists() && getLastModified() > imageFile.getLastModified()) {
+            LOGGER.fine("Found warm cache file \"" + path + "\"");
             try {
                 loadFromDisk();
                 return;
@@ -125,6 +126,7 @@ private void load() {
         }
 
         // Generate maps from image file
+        LOGGER.fine("Missed cache file \"" + path + "\"");
         try {
             generateFromImage();
             tryToWriteToDisk();

src/main/java/io/josemmo/bukkit/plugin/storage/SynchronizedFileStream.java

@@ -4,6 +4,9 @@
 import org.jetbrains.annotations.NotNull;
 import java.io.IOException;
 import java.io.RandomAccessFile;
+import java.nio.channels.FileChannel;
+import java.nio.channels.FileLock;
+import java.nio.channels.OverlappingFileLockException;
 import java.nio.file.Path;
 
 /**
@@ -17,10 +20,29 @@ public class SynchronizedFileStream extends RandomAccessFile {
      * @param readOnly Whether to open stream in read-only mode
      * @throws IOException if failed to acquire lock
      */
-    @Blocking
     public SynchronizedFileStream(@NotNull Path path, boolean readOnly) throws IOException {
         super(path.toFile(), readOnly ? "r" : "rw");
-        //noinspection ResultOfMethodCallIgnored
-        getChannel().lock(0L, Long.MAX_VALUE, readOnly);
+        waitForLock(readOnly);
+    }
+
+    /**
+     * Wait for lock to be released
+     * @param readOnly Whether to acquire read-only (shared) lock
+     */
+    @Blocking
+    private void waitForLock(boolean readOnly) throws IOException {
+        FileChannel channel = getChannel();
+        FileLock lock = null;
+        while (lock == null) {
+            try {
+                lock = channel.lock(0L, Long.MAX_VALUE, readOnly);
+            } catch (OverlappingFileLockException e) {
+                try {
+                    Thread.sleep(20);
+                } catch (InterruptedException __) {
+                    throw e;
+                }
+            }
+        }
     }
 }