org.apache.lucene.store
Class Lock

java.lang.Object
  extended by org.apache.lucene.store.Lock

public abstract class Lock
extends Object

An interprocess mutex lock.

Typical use might look like:

 new Lock.With(directory.makeLock("my.lock")) {
     public Object doBody() {
       ... code to execute while locked ...
     }
   }.run();
 

Version:
$Id: Lock.java 769409 2009-04-28 14:05:43Z mikemccand $
See Also:
Directory.makeLock(String)

Nested Class Summary
static class Lock.With
          Utility class for executing code with exclusive access.
 
Field Summary
protected  Throwable failureReason
          If a lock obtain called, this failureReason may be set with the "root cause" Exception as to why the lock was not obtained.
static long LOCK_OBTAIN_WAIT_FOREVER
          Pass this value to obtain(long) to try forever to obtain the lock.
static long LOCK_POLL_INTERVAL
          How long obtain(long) waits, in milliseconds, in between attempts to acquire the lock.
 
Constructor Summary
Lock()
           
 
Method Summary
abstract  boolean isLocked()
          Returns true if the resource is currently locked.
abstract  boolean obtain()
          Attempts to obtain exclusive access and immediately return upon success or failure.
 boolean obtain(long lockWaitTimeout)
          Attempts to obtain an exclusive lock within amount of time given.
abstract  void release()
          Releases exclusive access.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

LOCK_POLL_INTERVAL

public static long LOCK_POLL_INTERVAL
How long obtain(long) waits, in milliseconds, in between attempts to acquire the lock.


LOCK_OBTAIN_WAIT_FOREVER

public static final long LOCK_OBTAIN_WAIT_FOREVER
Pass this value to obtain(long) to try forever to obtain the lock.

See Also:
Constant Field Values

failureReason

protected Throwable failureReason
If a lock obtain called, this failureReason may be set with the "root cause" Exception as to why the lock was not obtained.

Constructor Detail

Lock

public Lock()
Method Detail

obtain

public abstract boolean obtain()
                        throws IOException
Attempts to obtain exclusive access and immediately return upon success or failure.

Returns:
true iff exclusive access is obtained
Throws:
IOException

obtain

public boolean obtain(long lockWaitTimeout)
               throws LockObtainFailedException,
                      IOException
Attempts to obtain an exclusive lock within amount of time given. Polls once per LOCK_POLL_INTERVAL (currently 1000) milliseconds until lockWaitTimeout is passed.

Parameters:
lockWaitTimeout - length of time to wait in milliseconds or LOCK_OBTAIN_WAIT_FOREVER to retry forever
Returns:
true if lock was obtained
Throws:
LockObtainFailedException - if lock wait times out
IllegalArgumentException - if lockWaitTimeout is out of bounds
IOException - if obtain() throws IOException

release

public abstract void release()
                      throws IOException
Releases exclusive access.

Throws:
IOException

isLocked

public abstract boolean isLocked()
Returns true if the resource is currently locked. Note that one must still call obtain() before using the resource.



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