StokeBloke.com

Recently I was working on a deadlock in our startup code.

It took some time to track it down as it never appeared as a deadlock (via CTRL-Break) it just stopped running with 0 CPU usage.

The cause was

 FileSystemView.getFileSystemView().getSystemIcon(file)

It appears that this call fails when called from multiple threads asking for the same system icon.

Below is an example on how to show the issue. Its was tested with Java 1.6.0_07

    public void testGetSystemIcon() throws IOException,
                                           InterruptedException {
        final FileImageThread t1 = new FileImageThread(".jpg");
        final FileImageThread t2 = new FileImageThread(".jpg");
        t1.start();
        t2.start();
        t1.join();
        t2.join();
    }

    public class FileImageThread extends Thread {
        final File file;

        public FileImageThread(final String suffix) throws IOException {
            file = File.createTempFile("test", suffix);
        }

        @Override
        public void run() {
            FileSystemView.getFileSystemView().getSystemIcon(file);
        }
    }

It does not hang every time, but it happens enough to be an issue.

The hang call stack is

Thread  id=22 name=Thread-4 inState=WAITING deadlocked=false isNative=false
  sun.misc.Unsafe.park(Native Method)
  java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
  java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:747)
  java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:905)
  java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1217)
  java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:218)
  java.util.concurrent.FutureTask.get(FutureTask.java:83)
  sun.awt.shell.Win32ShellFolderManager2$ComInvoker.invoke(Win32ShellFolderManager2.java:495)
  sun.awt.shell.Win32ShellFolder2.(Win32ShellFolder2.java:225)
  sun.awt.shell.Win32ShellFolderManager2.getDrives(Win32ShellFolderManager2.java:101)
  sun.awt.shell.Win32ShellFolderManager2.isFileSystemRoot(Win32ShellFolderManager2.java:323)
  sun.awt.shell.ShellFolder.isFileSystemRoot(ShellFolder.java:234)
  javax.swing.filechooser.FileSystemView.isFileSystemRoot(FileSystemView.java:310)
  com.osm.ui.FileImageUtilsTest$FileImageThread.run(FileImageUtilsTest.java:62)

Thread  id=21 name=Thread-3 inState=WAITING deadlocked=false isNative=false
  sun.misc.Unsafe.park(Native Method)
  java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
  java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:747)
  java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:905)
  java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1217)
  java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:218)
  java.util.concurrent.FutureTask.get(FutureTask.java:83)
  sun.awt.shell.Win32ShellFolderManager2$ComInvoker.invoke(Win32ShellFolderManager2.java:495)
  sun.awt.shell.Win32ShellFolder2.(Win32ShellFolder2.java:225)
  sun.awt.shell.Win32ShellFolderManager2.getDrives(Win32ShellFolderManager2.java:101)
  sun.awt.shell.Win32ShellFolderManager2.isFileSystemRoot(Win32ShellFolderManager2.java:323)
  sun.awt.shell.ShellFolder.isFileSystemRoot(ShellFolder.java:234)
  javax.swing.filechooser.FileSystemView.isFileSystemRoot(FileSystemView.java:310)
  com.osm.ui.FileImageUtilsTest$FileImageThread.run(FileImageUtilsTest.java:62)

No one else seemed to see this issue, but I saw it lots of times on my PC.

This entry was posted on Wednesday, March 18th, 2009 at 10:56 am and is filed under Programming. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.