[jira] [Resolved] (LUCENE-4755) Unmap MMapIndexInput's in a delayed way, and avoid WeakReference usage.

["Uwe Schindler (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-4755?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Uwe Schindler resolved LUCENE-4755.
-----------------------------------
    Resolution: Won't Fix

we no longer use weak references

> Unmap MMapIndexInput's in a delayed way, and avoid WeakReference usage.
> -----------------------------------------------------------------------
>
>                 Key: LUCENE-4755
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4755
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: core/store
>            Reporter: Kristofer Karlsson
>            Priority: Major
>
> (Most of this is shamelessly borrowed from Uwe Schindler)
> It would be nice to move away from using WeakReference to clean up clones.
> Instead, the clones could depend on the master by using a shared boolean closed-flag.
> In order to ensure visibility of this value, or at least make it less likely to crash, we could delay the unmapping operation.
> Rough suggestion of changes:
> {code:java}
> public class ByteBufferUnmapper {
>   /**
>    * <code>true</code>, if this platform supports unmapping mmapped files.
>    */
>   public static final boolean UNMAP_SUPPORTED;
>   private static final ScheduledExecutorService SCHEDULED_EXECUTOR_SERVICE = Executors.newSingleThreadScheduledExecutor(new NamedThreadFactory("unmapper-"));
>   static {
>     boolean v = false;
>     try {
>       Class.forName("sun.misc.Cleaner");
>       Class.forName("java.nio.DirectByteBuffer")
>         .getMethod("cleaner");
>       v = true;
>     } catch (Exception e) {
>       // Do nothing
>     } finally {
>       UNMAP_SUPPORTED = v;
>     }
>   }
>   public static void unmap(final ByteBuffer buffer) throws IOException {
>     try {
>       AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
>         public Object run() throws Exception {
>           Method getCleanerMethod = buffer.getClass().getMethod("cleaner");
>           getCleanerMethod.setAccessible(true);
>           final Object cleaner = getCleanerMethod.invoke(buffer);
>           if (cleaner != null) {
>             cleaner.getClass().getMethod("clean").invoke(cleaner);
>           }
>           return null;
>         }
>       });
>     } catch (PrivilegedActionException e) {
>       final IOException ioe = new IOException("unable to unmap the mapped buffer");
>       ioe.initCause(e.getCause());
>       throw ioe;
>     }
>   }
>   public static void unmapLater(final ByteBuffer buffer, long delay, TimeUnit unit) {
>     SCHEDULED_EXECUTOR_SERVICE.schedule(new Runnable() {
>       public void run() {
>         try {
>           unmap(buffer);
>         } catch (IOException e) {
>           e.printStackTrace();
>         }
>       }
>     }, delay, unit);
>   }
> }
> {code}
> {code:java}
> // MMapDirectory
>   final void cleanMapping(final ByteBuffer buffer) throws IOException {
>     if (useUnmapHack) {
>       ByteBufferUnmapper.unmapLater(buffer, 10, TimeUnit.SECONDS);
>     }
>   }
> {code}
> {code:java}
> // MMapIndexInput
>     @Override
>     public short readShort() throws IOException {
>       if (closed[0]) {
>         throw new AlreadyClosedException("MMapIndexInput already closed: " + this);
>       }
> {code}
> {code:java}
>     @Override
>     public void close() throws IOException {
>       try {
>         if (isClone || buffers == null) return;
>         closed[0] = true;
>         
>         // make local copy, then un-set early
>         final ByteBuffer[] bufs = buffers;
>         
>         for (final ByteBuffer b : bufs) {
>           cleanMapping(b);
>         }
>       } finally {
>         unsetBuffers();
>       }
>     }
> {code}



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