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## org.apache.lucene.index
Class ConcurrentMergeScheduler

    java.lang.Object
      org.apache.lucene.index.MergeScheduler
          org.apache.lucene.index.ConcurrentMergeScheduler

    public class ConcurrentMergeScheduler

extends MergeScheduler

A `MergeScheduler` that runs each merge using a separate thread, up until a maximum number of threads (`setMaxThreadCount(int)`) at which when a merge is needed, the thread(s) that are updating the index will pause until one or more merges completes. This is a simple way to use concurrency in the indexing process without having to create and manage application level threads.

Nested Class Summary
`protected class` | `ConcurrentMergeScheduler.MergeThread`

Field Summary
`protected Directory` | `dir`
`protected int` | `mergeThreadCount`
`protected List` | `mergeThreads`
`protected IndexWriter` | `writer`

Constructor Summary
`ConcurrentMergeScheduler()`

Method Summary
`static boolean` | `anyUnhandledExceptions()` Used for testing
`static void` | `clearUnhandledExceptions()`
`void` | `close()` Close this MergeScheduler.
`protected void` | `doMerge(MergePolicy.OneMerge merge)` Does the actual merge, by calling `IndexWriter.merge(org.apache.lucene.index.MergePolicy.OneMerge)`
`int` | `getMaxThreadCount()` Get the max # simultaneous threads that may be running.
`protected ConcurrentMergeScheduler.MergeThread` | `getMergeThread(IndexWriter writer, MergePolicy.OneMerge merge)` Create and return a new MergeThread
`int` | `getMergeThreadPriority()` Return the priority that merge threads run at.
`protected void` | `handleMergeException(Throwable exc)` Called when an exception is hit in a background merge thread
`void` | `merge(IndexWriter writer)` Run the merges provided by `IndexWriter.getNextMerge()`.
`void` | `setMaxThreadCount(int count)` Sets the max # simultaneous threads that may be running.
`void` | `setMergeThreadPriority(int pri)` Return the priority that merge threads run at.
`static void` | `setTestMode()`
`void` | `sync()`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### mergeThreads

    protected List mergeThreads

### dir

    protected Directory dir

### writer

    protected IndexWriter writer

### mergeThreadCount

    protected int mergeThreadCount

Constructor Detail

### ConcurrentMergeScheduler

    public ConcurrentMergeScheduler()

Method Detail

### setMaxThreadCount

    public void setMaxThreadCount(int count)

  Sets the max # simultaneous threads that may be running. If a merge is necessary yet we already have this many threads running, the incoming thread (that is calling add/updateDocument) will block until a merge thread has completed.

### getMaxThreadCount

    public int getMaxThreadCount()

  Get the max # simultaneous threads that may be running. @see #setMaxThreadCount.

### getMergeThreadPriority

    public int getMergeThreadPriority()

  Return the priority that merge threads run at. By default the priority is 1 plus the priority of (ie, slightly higher priority than) the first thread that calls merge.

### setMergeThreadPriority

    public void setMergeThreadPriority(int pri)

  Return the priority that merge threads run at.

### close

    public void close()

  Description copied from class: `MergeScheduler`
  Close this MergeScheduler.

### sync

    public void sync()

### merge

    public void merge(IndexWriter writer)
               throws CorruptIndexException,
                      IOException

  Description copied from class: `MergeScheduler`
  Run the merges provided by `IndexWriter.getNextMerge()`.

  Throws:
    `CorruptIndexException`
    `IOException`

### doMerge

    protected void doMerge(MergePolicy.OneMerge merge)
                    throws IOException

  Does the actual merge, by calling `IndexWriter.merge(org.apache.lucene.index.MergePolicy.OneMerge)`

  Throws:
    `IOException`

### getMergeThread

    protected ConcurrentMergeScheduler.MergeThread getMergeThread(IndexWriter writer,
                                                                  MergePolicy.OneMerge merge)
                                                           throws IOException

  Create and return a new MergeThread

  Throws:
    `IOException`

### handleMergeException

    protected void handleMergeException(Throwable exc)

  Called when an exception is hit in a background merge thread

### anyUnhandledExceptions

    public static boolean anyUnhandledExceptions()

  Used for testing

### clearUnhandledExceptions

    public static void clearUnhandledExceptions()

### setTestMode

    public static void setTestMode()

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