org.apache.lucene.search
Class ReferenceManager<G>

java.lang.Object
  extended by org.apache.lucene.search.ReferenceManager<G>
Type Parameters:
G - the concrete type that will be acquired and released.
All Implemented Interfaces:
Closeable
Direct Known Subclasses:
ReaderManager, SearcherManager

public abstract class ReferenceManager<G>
extends Object
implements Closeable

Utility class to safely share instances of a certain type across multiple threads, while periodically refreshing them. This class ensures each reference is closed only once all threads have finished using it. It is recommended to consult the documentation of ReferenceManager implementations for their maybeRefresh() semantics.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary
static interface ReferenceManager.RefreshListener
          Use to receive notification when a refresh has finished.
 
Field Summary
protected  G current
           
 
Constructor Summary
ReferenceManager()
           
 
Method Summary
 G acquire()
          Obtain the current reference.
 void addListener(ReferenceManager.RefreshListener listener)
          Adds a listener, to be notified when a reference is refreshed/swapped.
protected  void afterClose()
          Called after close(), so subclass can free any resources.
protected  void afterMaybeRefresh()
          Called after a refresh was attempted, regardless of whether a new reference was in fact created.
 void close()
           Closes this ReferenceManager to prevent future acquiring.
protected abstract  void decRef(G reference)
          Decrement reference counting on the given reference.
 boolean maybeRefresh()
          You must call this (or maybeRefreshBlocking()), periodically, if you want that acquire() will return refreshed instances.
 void maybeRefreshBlocking()
          You must call this (or maybeRefresh()), periodically, if you want that acquire() will return refreshed instances.
protected abstract  G refreshIfNeeded(G referenceToRefresh)
          Refresh the given reference if needed.
 void release(G reference)
          Release the reference previously obtained via acquire().
 void removeListener(ReferenceManager.RefreshListener listener)
          Remove a listener added with addListener(RefreshListener).
protected abstract  boolean tryIncRef(G reference)
          Try to increment reference counting on the given reference.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

current

protected volatile G current
Constructor Detail

ReferenceManager

public ReferenceManager()
Method Detail

decRef

protected abstract void decRef(G reference)
                        throws IOException
Decrement reference counting on the given reference.

Throws:
IOException - if reference decrement on the given resource failed.

refreshIfNeeded

protected abstract G refreshIfNeeded(G referenceToRefresh)
                              throws IOException
Refresh the given reference if needed. Returns null if no refresh was needed, otherwise a new refreshed reference.

Throws:
AlreadyClosedException - if the reference manager has been closed.
IOException - if the refresh operation failed

tryIncRef

protected abstract boolean tryIncRef(G reference)
                              throws IOException
Try to increment reference counting on the given reference. Return true if the operation was successful.

Throws:
AlreadyClosedException - if the reference manager has been closed.
IOException

acquire

public final G acquire()
                throws IOException
Obtain the current reference. You must match every call to acquire with one call to release(G); it's best to do so in a finally clause, and set the reference to null to prevent accidental usage after it has been released.

Throws:
AlreadyClosedException - if the reference manager has been closed.
IOException

close

public final void close()
                 throws IOException

Closes this ReferenceManager to prevent future acquiring. A reference manager should be closed if the reference to the managed resource should be disposed or the application using the ReferenceManager is shutting down. The managed resource might not be released immediately, if the ReferenceManager user is holding on to a previously acquired reference. The resource will be released once when the last reference is released. Those references can still be used as if the manager was still active.

Applications should not acquire new references from this manager once this method has been called. Acquiring a resource on a closed ReferenceManager will throw an AlreadyClosedException.

Specified by:
close in interface Closeable
Throws:
IOException - if the underlying reader of the current reference could not be closed

afterClose

protected void afterClose()
                   throws IOException
Called after close(), so subclass can free any resources.

Throws:
IOException - if the after close operation in a sub-class throws an IOException

maybeRefresh

public final boolean maybeRefresh()
                           throws IOException
You must call this (or maybeRefreshBlocking()), periodically, if you want that acquire() will return refreshed instances.

Threads: it's fine for more than one thread to call this at once. Only the first thread will attempt the refresh; subsequent threads will see that another thread is already handling refresh and will return immediately. Note that this means if another thread is already refreshing then subsequent threads will return right away without waiting for the refresh to complete.

If this method returns true it means the calling thread either refreshed or that there were no changes to refresh. If it returns false it means another thread is currently refreshing.

Throws:
IOException - if refreshing the resource causes an IOException
AlreadyClosedException - if the reference manager has been closed.

maybeRefreshBlocking

public final void maybeRefreshBlocking()
                                throws IOException
You must call this (or maybeRefresh()), periodically, if you want that acquire() will return refreshed instances.

Threads: unlike maybeRefresh(), if another thread is currently refreshing, this method blocks until that thread completes. It is useful if you want to guarantee that the next call to acquire() will return a refreshed instance. Otherwise, consider using the non-blocking maybeRefresh().

Throws:
IOException - if refreshing the resource causes an IOException
AlreadyClosedException - if the reference manager has been closed.

afterMaybeRefresh

protected void afterMaybeRefresh()
                          throws IOException
Called after a refresh was attempted, regardless of whether a new reference was in fact created.

Throws:
IOException - if a low level I/O exception occurs

release

public final void release(G reference)
                   throws IOException
Release the reference previously obtained via acquire().

NOTE: it's safe to call this after close().

Throws:
IOException - if the release operation on the given resource throws an IOException

addListener

public void addListener(ReferenceManager.RefreshListener listener)
Adds a listener, to be notified when a reference is refreshed/swapped.


removeListener

public void removeListener(ReferenceManager.RefreshListener listener)
Remove a listener added with addListener(RefreshListener).



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