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