ZKInterProcessLockBase (Apache HBase 1.2.12 API)

java.lang.Object
- org.apache.hadoop.hbase.zookeeper.lock.ZKInterProcessLockBase

All Implemented Interfaces:

InterProcessLock

Direct Known Subclasses:

ZKInterProcessReadLock, ZKInterProcessWriteLock
```
@InterfaceAudience.Private
public abstract class ZKInterProcessLockBase
extends Object
implements InterProcessLock
```
ZooKeeper based HLock implementation. Based on the Shared Locks recipe. (see: ZooKeeper Recipes and Solutions )

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`protected static class`	`ZKInterProcessLockBase.AcquiredLock` Represents information about a lock held by this thread.
`protected static class`	`ZKInterProcessLockBase.ZNodeComparator`

Nested classes/interfaces inherited from interface org.apache.hadoop.hbase.InterProcessLock
InterProcessLock.MetadataHandler

Field Summary

Fields
Modifier and Type	Field and Description
`protected AtomicReference<ZKInterProcessLockBase.AcquiredLock>`	`acquiredLock`
`protected String`	`childZNode`
`protected String`	`fullyQualifiedZNode`
`protected InterProcessLock.MetadataHandler`	`handler`
`private static org.apache.commons.logging.Log`	`LOG`
`protected byte[]`	`metadata`
`protected String`	`parentLockNode`
`protected static String`	`READ_LOCK_CHILD_NODE_PREFIX` ZNode prefix used by processes acquiring reader locks
`protected static String`	`WRITE_LOCK_CHILD_NODE_PREFIX` ZNode prefix used by processes acquiring writer locks
`protected ZooKeeperWatcher`	`zkWatcher`

Constructor Summary

Constructors
Modifier	Constructor and Description
`protected`	`ZKInterProcessLockBase(ZooKeeperWatcher zkWatcher, String parentLockNode, byte[] metadata, InterProcessLock.MetadataHandler handler, String childNode)` Called by implementing classes.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`acquire()` Acquire the lock, waiting indefinitely until the lock is released or the thread is interrupted.
`private String`	`createLockZNode()`
`protected abstract String`	`getLockPath(String myZNode, List<String> children)` Determine based on a list of children under a ZNode, whether or not a process which created a specified ZNode has obtained a lock.
`protected boolean`	`handleLockMetadata(String lockZNode)` Process metadata stored in a ZNode using a callback
`protected boolean`	`handleLockMetadata(String lockZNode, InterProcessLock.MetadataHandler handler)` Process metadata stored in a ZNode using a callback object passed to this instance.
`protected boolean`	`isChildOfSameType(String child)` Check if a child znode represents the same type(read or write) of lock
`protected static boolean`	`isChildReadLock(String child)` Check if a child znode represents a read lock.
`protected static boolean`	`isChildWriteLock(String child)` Check if a child znode represents a write lock.
`void`	`reapAllLocks()` If supported, attempts to reap all the locks of this type by forcefully deleting the locks (both held and attempted).
`void`	`reapExpiredLocks(long timeout)` Will delete all lock znodes of this type (either read or write) which are "expired" according to timeout.
`void`	`release()` Release the lock.
`boolean`	`tryAcquire(long timeoutMs)` Acquire the lock within a wait time.
`protected void`	`updateAcquiredLock(String createdZNode)` Update state as to indicate that a lock is held
`void`	`visitLocks(InterProcessLock.MetadataHandler handler)` Visits the locks (both held and attempted) with the given MetadataHandler.

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

- Field Detail
  - LOG
```
private static final org.apache.commons.logging.Log LOG
```
  - READ_LOCK_CHILD_NODE_PREFIX
```
protected static final String READ_LOCK_CHILD_NODE_PREFIX
```
    ZNode prefix used by processes acquiring reader locks
    
    See Also:
    Constant Field Values
  - WRITE_LOCK_CHILD_NODE_PREFIX
```
protected static final String WRITE_LOCK_CHILD_NODE_PREFIX
```
    ZNode prefix used by processes acquiring writer locks
    
    See Also:
    Constant Field Values
  - zkWatcher
```
protected final ZooKeeperWatcher zkWatcher
```
  - parentLockNode
```
protected final String parentLockNode
```
  - fullyQualifiedZNode
```
protected final String fullyQualifiedZNode
```
  - childZNode
```
protected final String childZNode
```
  - metadata
```
protected final byte[] metadata
```
  - handler
```
protected final InterProcessLock.MetadataHandler handler
```
  - acquiredLock
```
protected final AtomicReference<ZKInterProcessLockBase.AcquiredLock> acquiredLock
```
- Constructor Detail
  - ZKInterProcessLockBase
```
protected ZKInterProcessLockBase(ZooKeeperWatcher zkWatcher,
                      String parentLockNode,
                      byte[] metadata,
                      InterProcessLock.MetadataHandler handler,
                      String childNode)
```
    Called by implementing classes.
    
    Parameters:
    zkWatcher -
    parentLockNode - The lock ZNode path
    metadata -
    handler -
    childNode - The prefix for child nodes created under the parent
- Method Detail
  - acquire
```
public void acquire()
             throws IOException,
                    InterruptedException
```
    Acquire the lock, waiting indefinitely until the lock is released or the thread is interrupted.
    
    Specified by:
    
    acquire in interface InterProcessLock
    
    Throws:
    
    IOException - If there is an unrecoverable error releasing the lock
    
    InterruptedException - If current thread is interrupted while waiting for the lock
  - tryAcquire
```
public boolean tryAcquire(long timeoutMs)
                   throws IOException,
                          InterruptedException
```
    Acquire the lock within a wait time.
    
    Specified by:
    
    tryAcquire in interface InterProcessLock
    
    Parameters:
    timeoutMs - The maximum time (in milliseconds) to wait for the lock, -1 to wait indefinitely
    
    Returns:
    True if the lock was acquired, false if waiting time elapsed before the lock was acquired
    
    Throws:
    
    IOException - If there is an unrecoverable error talking talking (e.g., when talking to a lock service) when acquiring the lock
    
    InterruptedException - If the thread is interrupted while waiting to acquire the lock
  - createLockZNode
```
private String createLockZNode()
                        throws org.apache.zookeeper.KeeperException
```
    Throws:
    
    org.apache.zookeeper.KeeperException
  - isChildReadLock
```
protected static boolean isChildReadLock(String child)
```
    Check if a child znode represents a read lock.
    
    Parameters:
    child - The child znode we want to check.
    
    Returns:
    whether the child znode represents a read lock
  - isChildWriteLock
```
protected static boolean isChildWriteLock(String child)
```
    Check if a child znode represents a write lock.
    
    Parameters:
    child - The child znode we want to check.
    
    Returns:
    whether the child znode represents a write lock
  - isChildOfSameType
```
protected boolean isChildOfSameType(String child)
```
    Check if a child znode represents the same type(read or write) of lock
    
    Parameters:
    child - The child znode we want to check.
    
    Returns:
    whether the child znode represents the same type(read or write) of lock
  - updateAcquiredLock
```
protected void updateAcquiredLock(String createdZNode)
                           throws IOException
```
    Update state as to indicate that a lock is held
    
    Parameters:
    createdZNode - The lock znode
    
    Throws:
    
    IOException - If an unrecoverable ZooKeeper error occurs
  - release
```
public void release()
             throws IOException,
                    InterruptedException
```
    Release the lock.
    
    Specified by:
    
    release in interface InterProcessLock
    
    Throws:
    
    IOException - If there is an unrecoverable error releasing the lock
    
    InterruptedException - If the thread is interrupted while releasing the lock
  - handleLockMetadata
```
protected boolean handleLockMetadata(String lockZNode)
```
    Process metadata stored in a ZNode using a callback
    
    Parameters:
    lockZNode - The node holding the metadata
    
    Returns:
    True if metadata was ready and processed, false otherwise.
  - handleLockMetadata
```
protected boolean handleLockMetadata(String lockZNode,
                         InterProcessLock.MetadataHandler handler)
```
    Process metadata stored in a ZNode using a callback object passed to this instance.
    
    Parameters:
    lockZNode - The node holding the metadata
    handler - the metadata handler
    
    Returns:
    True if metadata was ready and processed, false on exception.
  - reapAllLocks
```
public void reapAllLocks()
                  throws IOException
```
    Description copied from interface: InterProcessLock
    
    If supported, attempts to reap all the locks of this type by forcefully deleting the locks (both held and attempted). Lock reaping is different than coordinated lock revocation in that, there is no coordination, and the behavior is undefined if the lock holder is still alive. Calling this should have the same affect as calling InterProcessLock.reapExpiredLocks(long) with timeout=0.
    
    Specified by:
    
    reapAllLocks in interface InterProcessLock
    
    Throws:
    
    IOException - If there is an unrecoverable error reaping the locks
  - reapExpiredLocks
```
public void reapExpiredLocks(long timeout)
                      throws IOException
```
    Will delete all lock znodes of this type (either read or write) which are "expired" according to timeout. Assumption is that the clock skew between zookeeper and this servers is negligible. Referred in zk recipe as "Revocable Shared Locks with Freaking Laser Beams". (http://zookeeper.apache.org/doc/trunk/recipes.html).
    
    Specified by:
    
    reapExpiredLocks in interface InterProcessLock
    
    Throws:
    
    IOException - If there is an unrecoverable error reaping the locks
  - visitLocks
```
public void visitLocks(InterProcessLock.MetadataHandler handler)
                throws IOException
```
    Visits the locks (both held and attempted) with the given MetadataHandler.
    
    Specified by:
    
    visitLocks in interface InterProcessLock
    
    Throws:
    
    IOException - If there is an unrecoverable error
  - getLockPath
```
protected abstract String getLockPath(String myZNode,
                 List<String> children)
                               throws IOException
```
    Determine based on a list of children under a ZNode, whether or not a process which created a specified ZNode has obtained a lock. If a lock is not obtained, return the path that we should watch awaiting its deletion. Otherwise, return null. This method is abstract as the logic for determining whether or not a lock is obtained depends on the type of lock being implemented.
    
    Parameters:
    myZNode - The ZNode created by the process attempting to acquire a lock
    children - List of all child ZNodes under the lock's parent ZNode
    
    Returns:
    The path to watch, or null if myZNode can represent a correctly acquired lock.
    
    Throws:
    
    IOException

Class ZKInterProcessLockBase

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.hadoop.hbase.InterProcessLock

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

LOG

READ_LOCK_CHILD_NODE_PREFIX

WRITE_LOCK_CHILD_NODE_PREFIX

zkWatcher

parentLockNode

fullyQualifiedZNode

childZNode

metadata

handler

acquiredLock

Constructor Detail

ZKInterProcessLockBase

Method Detail

acquire

tryAcquire

createLockZNode

isChildReadLock

isChildWriteLock

isChildOfSameType

updateAcquiredLock

release

handleLockMetadata

handleLockMetadata

reapAllLocks

reapExpiredLocks

visitLocks

getLockPath