Question

My guesses were wrong, and had nothing to do with the answer. This question is no longer valid. See my answer. Sorry about this poor question.

Tl;dr Version

Why can’t a Java process find a certain file, until another process – the process that created that file – has finished executing. Can this be worked around?

Longer Version

I have an application that needs to restart itself (it just needs to, okay?). The first time, it creates a File and then serializes an object there. This is done with a FileOutputStream/ObjectOutputStream combo, as described below:

private static File serializeBootstrapInfoIntoFile(
    final BootstrapInfo info) throws IOException {

  final File tempFile = File.createTempFile("BobBootstrapInfo", null);
  final FileOutputStream fos = new FileOutputStream(tempFile);
  final ObjectOutputStream oos = new ObjectOutputStream(fos);
  oos.writeObject(info);

  // just being thorough
  oos.flush();
  oos.close();
  fos.flush();
  fos.close();

  return tempFile;
}

After this, I create another java process with a System.exec()-call, to which I pass the the absolute path of the returned tempFile as a system property. The other java process should then open the file, and deserialize the containing Object. The first process remains alive until the spawned process exits, since it handles the new one’s output/error streams.

The problem is, however, that the second process doesn’t seem to find the file, and dies always in a FileNotFoundException during deserialization (I’ve confirmed this with a file.exists()).

When I check manually afterwards, the file does indeed exist. Also, if I manually run the exact same command line that is passed to the System.exec(), it runs fine. So, I’m guessing the first process somehow manages to hide the file from the new process, or fails to actually write the file to the file system, even the streams are flushed and closed. I also tried with Thread.sleep(10000) on the first thread, to let the IO operations to finish, but that didn’t help a bit.

Am I doing something wrong? Or is this a Java thing, or maybe an OSX thing (which I’m running with atm)?

Answers to Comments

I’m running OS X 10.6.3, and the Java version is 1.6.0_20.

The System.exec() arguments are

java
-classpath
/var/folders/dr/drDlHsguGvq0zF2Jtgn4S++++TI/-Tmp-/bob7168396245507677201.tmp:/Users/wolfie/Documents/workspace/Bob/dist/lib/junit.jar:/Users/wolfie/Documents/workspace/Bob/dist/lib/bob.jar
-Dcache.location="/var/folders/dr/drDlHsguGvq0zF2Jtgn4S++++TI/-Tmp-/BobBootstrapInfo4944987280015634213.tmp"
com.github.wolfie.bob.Bob

where each line is an element in a String array. The /var/folders/dr/drDlHsguGvq0zF2Jtgn4S++++TI/-Tmp-/BobBootstrapInfo4606780571989099166.tmp-file is the one that was created, and being read by the other thread. The envp and dir arguments are null.

The whole stacktrace is:

Exception in thread "main" com.github.wolfie.bob.BootstrapError: java.io.FileNotFoundException: "/var/folders/dr/drDlHsguGvq0zF2Jtgn4S++++TI/-Tmp-/BobBootstrapInfo4606780571989099166.tmp" (No such file or directory)
    at com.github.wolfie.bob.Bob.getBootstrapInfo(Bob.java:186)
    at com.github.wolfie.bob.Bob.run(Bob.java:138)
    at com.github.wolfie.bob.Bob.main(Bob.java:95)
Caused by: java.io.FileNotFoundException: "/var/folders/dr/drDlHsguGvq0zF2Jtgn4S++++TI/-Tmp-/BobBootstrapInfo4606780571989099166.tmp" (No such file or directory)
    at java.io.FileInputStream.open(Native Method)
    at java.io.FileInputStream.(FileInputStream.java:106)
    at com.github.wolfie.bob.Bob.deserializeBootstrapInfoFromFile(Bob.java:265)
    at com.github.wolfie.bob.Bob.getBootstrapInfo(Bob.java:184)
    ... 2 more

Answer 1

The answer isn’t visible from the question: I defined the system property like so:

-Dcache.location="/foo/file.ext"

But the property should’ve been instead

-Dcache.location=/foo/file.ext

i.e. without the quotes. This, apparently, was ignored when the exact same arguments were passed from the command line, probably because Bash processed them in a different way to the JVM.

Sorry about the poor question.