File.renameTo method question

[Jiang Lin]

01 public class FileProcessor() {
02   private File dir,
03   private String instanceId;
04   private FileProcessor(String dirName, String instanceId) {
05     this.dir = new File(dirName);
06     this.instanceId = instanceId;
07   }
08   private void run(File dir) throws Exception {
09     // gets all the files with the extension "Incoming"
10     FileFilter extFilter = new FileExtensionFilter(instanceId + ".Incoming");
11     File[] files = dir.listFiles(extFilter);
12     for (int i = 0; files != null && i < files.length; i++) {
13       // renames the extension from "Incoming" to InProcess"
14       File file = renameExtension(dir, files[i], instanceId + ".Incoming", instanceId + ".InProcess");
15       process(file);
16       // renames the file extension from "InProcess" to "Done"
17       renameExtension(dir, file, instanceId + ".InProcess", instanceId + ".Done");
18     }
19   }
20   private void process(File file) {{
21     Thread.sleep(5000);
22     System.out.println("Processing the file '" + file + "'...");
23   }
24   private File renameExtension(File dir, File file, String oldExt, String newExt) {
25     // gets the new file name with the old extension replaced by the new one
26     String newName = stripExtension(file, oldExt) + newExt;
27     File newFile = new File(dir, newName);
28     if (!file.renameTo(newFile)) {
29       throw new Exception("Attempt to rename '" + file + "' to '" + newFile + "' failed");
30     }
31     return newFile;
32   }
33   private static String stripExtension(File file, String ext) {
34     // strip off the given extension from the file name
35     String name = file.getName();
36     int len = name.length();
37     int extLen = ext.length();
38     return name.substring(0, len - extLen);
39   }
40   public static void main(String[] args) throws Exception {
41     String dirName = args[0];
42     String id = args[1];
43     FileProcessor instance = new FileProcessor(dirName, id);
44     instance.run();
45   }
46 }

When running the multiple instances of the above class concurrently
1) from different JVM
2) against the same directory
3) with different instance id (so that multiple instances will not operate on the same file)
the line 28 file.renameTo() method returns false, even though when the file name is successfully renamed.
However, when Thread.sleep() method call in line 21 is commented out, the problem does not occur anymore.
Any idea why the return value of file.renameTo method call indicates a failure when in fact it really worked? Could this be a coding issue, JVM issue (Java 1.3.1), or OS issue (NT 4.0)?
Any insights are greatly appreciated.
Jiang
[ April 02, 2004: Message edited by: Jiang Lin ]

[Jim Yingst]

Any idea why the return value of file.renameTo method call indicates a failure when in fact it really worked?
Are you sure it really worked? One reason renameTo() may fail is if there's already a file matching the new name. If you run your program more than once, maybe the file got moved correctly the first time. On subsequent attempts the rename fails, because the previously moved file is still there. But it looks as though you've moved it successfully, because there's a file there where you expect the renamed file to be. Try checking if (newFile.exists()) in your method.

[Jiang Lin]

Thanks very much, Jim. That was exactly the problem. There was a bug in instantiating the file filer at line 10, so the instances "saw" the files that were supposed to belong to others and processed them before the supposed owner picked them up...
Thanks again. I very much appreciate your help.
Jiang Lin