From 2863dd0acc86655ab52ee28f9687fbdb0144d92e Mon Sep 17 00:00:00 2001
From: Mike Primm <mike@primmhome.com>
Date: Tue, 28 Jun 2011 22:33:11 -0500
Subject: [PATCH] Put timeout on read lock used by web server - make sure it
 can't be indefinite

---
 .../java/org/dynmap/utils/FileLockManager.java   | 16 +++++++++++++++-
 .../dynmap/web/handlers/FilesystemHandler.java   |  5 ++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/main/java/org/dynmap/utils/FileLockManager.java b/src/main/java/org/dynmap/utils/FileLockManager.java
index 8994b32c..71048616 100644
--- a/src/main/java/org/dynmap/utils/FileLockManager.java
+++ b/src/main/java/org/dynmap/utils/FileLockManager.java
@@ -63,9 +63,16 @@ public class FileLockManager {
      * Get read lock on file - multiple readers allowed, blocks writers
      */
     public static boolean getReadLock(File f) {
+        return getReadLock(f, -1);
+    }
+    /**
+     * Get read lock on file - multiple readers allowed, blocks writers - with timeout (msec)
+     */
+    public static boolean getReadLock(File f, long timeout) {
         String fn = f.getPath();
         synchronized(lock) {
             boolean got_lock = false;
+            boolean first_wait = true;
             while(!got_lock) {
                 Integer lockcnt = filelocks.get(fn);    /* Get lock count */
                 if(lockcnt == null) {
@@ -78,7 +85,14 @@ public class FileLockManager {
                 }
                 else {  /* Write lock in place */
                     try {
-                        lock.wait();
+                        if((timeout > 0) && (!first_wait)) {    /* We already waited */
+                            return false;
+                        }
+                        if(timeout < 0)
+                            lock.wait();
+                        else
+                            lock.wait(timeout);
+                        first_wait = false;
                     } catch (InterruptedException ix) {
                         Log.severe("getReadLock(" + fn + ") interrupted");
                         return false;
diff --git a/src/main/java/org/dynmap/web/handlers/FilesystemHandler.java b/src/main/java/org/dynmap/web/handlers/FilesystemHandler.java
index 510f0e85..07bc089a 100644
--- a/src/main/java/org/dynmap/web/handlers/FilesystemHandler.java
+++ b/src/main/java/org/dynmap/web/handlers/FilesystemHandler.java
@@ -23,7 +23,10 @@ public class FilesystemHandler extends FileHandler {
     @Override
     protected InputStream getFileInput(String path, HttpRequest request, HttpResponse response) {
         File file = new File(root, path);
-        FileLockManager.getReadLock(file);
+        if(!FileLockManager.getReadLock(file, 5000)) {    /* Wait up to 5 seconds for lock */
+            Log.severe("Timeout waiting for lock on file " + file.getPath());
+            return null;
+        }
         FileInputStream result = null;
         try {
             if (file.getCanonicalPath().startsWith(root.getAbsolutePath()) && file.isFile()) {