GenericLock (Commons Transaction 1.3-SNAPSHOT API)

java.lang.Object
- org.apache.commons.transaction.locking.GenericLock

All Implemented Interfaces:

MultiLevelLock, MultiLevelLock2

Direct Known Subclasses:

ReadWriteLock, ReadWriteUpgradeLock
```
public class GenericLock
extends Object
implements MultiLevelLock2
```
A generic implementain of a simple multi level lock.
The idea is to have an ascending number of lock levels ranging from 0 to maxLockLevel as specified in GenericLock(Object, int, LoggerFacade): the higher the lock level the stronger and more restrictive the lock. To determine which lock may coexist with other locks you have to imagine matching pairs of lock levels. For each pair both parts allow for all lock levels less than or equal to the matching other part. Pairs are composed by the lowest and highest level not yet part of a pair and successively applying this method until no lock level is left. For an even amount of levels each level is part of exactly one pair. For an odd amount the middle level is paired with itself. The highst lock level may coexist with the lowest one (0) which by definition means NO LOCK. This implies that you will have to specify at least one other lock level and thus set maxLockLevel to at least 1.

Although this may sound complicated, in practice this is quite simple. Let us imagine you have three lock levels:
- 0:NO LOCK (always needed by the implementation of this lock)
- 1:SHARED
- 2:EXCLUSIVE
Accordingly, you will have to set maxLockLevel to 2. Now, there are two pairs of levels
- NO LOCK with EXCLUSIVE
- SHARED with SHARED
This means when the current highest lock level is NO LOCK everything less or equal to EXCLUSIVE is allowed - which means every other lock level. On the other side EXCLUSIVE allows exacly for NO LOCK- which means nothing else. In conclusion, SHARED allows for SHARED or NO LOCK, but not for EXCLUSIVE. To make this very clear have a look at this table, where o means compatible or can coexist and x means incompatible or can not coexist:

NO LOCK SHARED EXCLUSIVE

NO LOCK o o o

SHARED o o x

EXCLUSIVE o x x

Additionally, there are preferences for specific locks you can pass to acquire(Object, int, boolean, int, boolean, long). This means whenever more thanone party waits for a lock you can specify which one is to be preferred. This gives you every freedom you might need to specifcy e.g.
- priority to parties either applying for higher or lower lock levels
- priority not only to higher or lower locks, but to a specific level
- completely random preferences
Version:

$Id: GenericLock.java 493628 2007-01-07 01:42:48Z joerg $

Nested Class Summary

Nested Classes
Modifier and Type Class and Description

protected static class GenericLock.LockOwner

Nested Classes
Modifier and Type	Class and Description
`protected static class`	`GenericLock.LockOwner`

Field Summary

Fields
Modifier and Type	Field and Description
`protected LoggerFacade`	`logger`
`protected Map`	`owners`
`protected Object`	`resourceId`
`protected int`	`waiters`
`protected List`	`waitingOwners`

Fields inherited from interface org.apache.commons.transaction.locking.MultiLevelLock2
COMPATIBILITY_NONE, COMPATIBILITY_REENTRANT, COMPATIBILITY_REENTRANT_AND_SUPPORT, COMPATIBILITY_SUPPORT

Constructor Summary

Constructors
Constructor and Description

GenericLock(Object resourceId, int maxLockLevel, LoggerFacade logger)
Creates a new lock.

Constructors
Constructor and Description
`GenericLock(Object resourceId, int maxLockLevel, LoggerFacade logger)` Creates a new lock.

Method Summary

Methods
Modifier and Type	Method and Description
`boolean`	`acquire(Object ownerId, int targetLockLevel, boolean wait, boolean reentrant, long timeoutMSecs)` Tries to acquire a certain lock level on this lock.
`boolean`	`acquire(Object ownerId, int targetLockLevel, boolean wait, int compatibility, boolean preferred, long timeoutMSecs)` Tries to acquire a certain lock level on this lock.
`boolean`	`acquire(Object ownerId, int targetLockLevel, boolean wait, int compatibility, long timeoutMSecs)`
`boolean`	`acquire(Object ownerId, int targetLockLevel, boolean preferred, long timeoutMSecs)` Tries to blockingly acquire a lock which can be preferred.
`boolean`	`equals(Object o)`
`protected Set`	`getConflictingOwners(GenericLock.LockOwner myOwner, Collection ownersToTest)`
`protected Set`	`getConflictingOwners(Object ownerId, int targetLockLevel, int compatibility)`
`protected Collection`	`getConflictingWaiters(Object ownerId)`
`int`	`getLevelMaxLock()` Gets the highst lock level possible.
`int`	`getLevelMinLock()` Gets the lowest lock level possible.
`int`	`getLockLevel(Object ownerId)` Retuns the highest lock level the specified owner holds on this lock or `0` if it holds no locks at all.
`protected GenericLock.LockOwner`	`getMaxLevelOwner()`
`protected GenericLock.LockOwner`	`getMaxLevelOwner(GenericLock.LockOwner reentrantOwner, boolean preferred)`
`protected GenericLock.LockOwner`	`getMaxLevelOwner(GenericLock.LockOwner reentrantOwner, int supportLockLevel, boolean preferred)`
`protected GenericLock.LockOwner`	`getMaxLevelOwner(int supportLockLevel, boolean preferred)`
`Object`	`getOwner()`
`Object`	`getResourceId()` Gets the resource assotiated to this lock.
`boolean`	`has(Object ownerId, int lockLevel)` Tests if a certain lock level is owned by an owner.
`int`	`hashCode()`
`protected boolean`	`isCompatible(int targetLockLevel, int currentLockLevel)`
`protected void`	`registerWaiter(GenericLock.LockOwner waitingOwner)`
`boolean`	`release(Object ownerId)` Releases any lock levels the specified owner may hold on this lock.
`protected void`	`setLockLevel(Object ownerId, GenericLock.LockOwner lock, int targetLockLevel, int compatibility, boolean intention)`
`boolean`	`test(Object ownerId, int targetLockLevel, int compatibility)` Tests if a certain lock level could be acquired.
`String`	`toString()`
`protected boolean`	`tryLock(Object ownerId, int targetLockLevel, int compatibility, boolean preferred)`
`protected boolean`	`tryLock(Object ownerId, int targetLockLevel, int compatibility, boolean preferred, boolean tryOnly)`
`protected void`	`unregisterWaiter(GenericLock.LockOwner waitingOwner)`

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

- Field Detail
  - resourceId
```
protected Object resourceId
```
  - owners
```
protected Map owners
```
  - waitingOwners
```
protected List waitingOwners
```
  - logger
```
protected LoggerFacade logger
```
  - waiters
```
protected int waiters
```
- Constructor Detail
  - GenericLock
```
public GenericLock(Object resourceId,
           int maxLockLevel,
           LoggerFacade logger)
```
    Creates a new lock.
    
    Parameters:
    resourceId - identifier for the resource associated to this lock
    maxLockLevel - highest allowed lock level as described in class intro
    logger - generic logger used for all kind of debug logging
- Method Detail
  - equals
```
public boolean equals(Object o)
```
    Overrides:
    
    equals in class Object
  - hashCode
```
public int hashCode()
```
    Overrides:
    
    hashCode in class Object
  - test
```
public boolean test(Object ownerId,
           int targetLockLevel,
           int compatibility)
```
    Description copied from interface: MultiLevelLock2
    
    Tests if a certain lock level could be acquired. This method tests only and does not actually acquire the lock.
    
    Specified by:
    
    test in interface MultiLevelLock2
    
    Parameters:
    ownerId - a unique id identifying the entity that wants to test a certain lock level on this lock
    targetLockLevel - the lock level to acquire
    compatibility - MultiLevelLock2.COMPATIBILITY_NONEif no additional compatibility is desired (same as reentrant set to false) , MultiLevelLock2.COMPATIBILITY_REENTRANTif lock level by the same owner shall not affect compatibility (same as reentrant set to true), or MultiLevelLock2.COMPATIBILITY_SUPPORTif lock levels that are the same as the desired shall not affect compatibility, or finally MultiLevelLock2.COMPATIBILITY_REENTRANT_AND_SUPPORTwhich is a combination of reentrant and support
    
    Returns:
    true if the lock could be acquired at the time this method was called
    See Also:
    MultiLevelLock2.test(Object, int, int)
  - has
```
public boolean has(Object ownerId,
          int lockLevel)
```
    Description copied from interface: MultiLevelLock2
    
    Tests if a certain lock level is owned by an owner.
    
    Specified by:
    
    has in interface MultiLevelLock2
    
    Parameters:
    ownerId - a unique id identifying the entity that wants to check a certain lock level on this lock
    lockLevel - the lock level to test
    
    Returns:
    true if the lock could be acquired at the time this method was called
    See Also:
    MultiLevelLock2.has(Object, int)
  - acquire
```
public boolean acquire(Object ownerId,
              int targetLockLevel,
              boolean wait,
              boolean reentrant,
              long timeoutMSecs)
                throws InterruptedException
```
    Description copied from interface: MultiLevelLock
    
    Tries to acquire a certain lock level on this lock.
    
    Specified by:
    
    acquire in interface MultiLevelLock
    
    Parameters:
    ownerId - a unique id identifying the entity that wants to acquire a certain lock level on this lock
    targetLockLevel - the lock level to acquire
    wait - true if this method shall block when the desired lock level can not be acquired
    reentrant - true if lock levels of the same entity acquired earlier should not restrict compatibility with the lock level desired now
    timeoutMSecs - if blocking is enabled by the wait parameter this specifies the maximum wait time in milliseconds
    
    Returns:
    true if the lock actually was acquired
    
    Throws:
    
    InterruptedException - when the thread waiting on this method is interrupted
    See Also:
    MultiLevelLock.acquire(java.lang.Object, int, boolean, boolean, long)
  - acquire
```
public boolean acquire(Object ownerId,
              int targetLockLevel,
              boolean wait,
              int compatibility,
              long timeoutMSecs)
                throws InterruptedException
```
    Throws:
    
    InterruptedException
    See Also:
    acquire(Object, int, boolean, int, boolean, long)
  - acquire
```
public boolean acquire(Object ownerId,
              int targetLockLevel,
              boolean preferred,
              long timeoutMSecs)
                throws InterruptedException
```
    Tries to blockingly acquire a lock which can be preferred.
    
    Throws:
    
    InterruptedException
    Since:
    
    1.1
    
    See Also:
    acquire(Object, int, boolean, int, boolean, long)
  - acquire
```
public boolean acquire(Object ownerId,
              int targetLockLevel,
              boolean wait,
              int compatibility,
              boolean preferred,
              long timeoutMSecs)
                throws InterruptedException
```
    Description copied from interface: MultiLevelLock2
    
    Tries to acquire a certain lock level on this lock. Does the same as MultiLevelLock.acquire(java.lang.Object, int, boolean, boolean, long) except that it allows for different compatibility settings. There is an additional compatibility mode MultiLevelLock2.COMPATIBILITY_SUPPORTthat allows equal lock levels not to interfere with each other. This is like an additional shared compatibility and useful when you only want to make sure not to interfer with lowe levels, but are fine with the same.
    
    Specified by:
    
    acquire in interface MultiLevelLock2
    
    Parameters:
    ownerId - a unique id identifying the entity that wants to acquire a certain lock level on this lock
    targetLockLevel - the lock level to acquire
    wait - true if this method shall block when the desired lock level can not be acquired
    compatibility - MultiLevelLock2.COMPATIBILITY_NONEif no additional compatibility is desired (same as reentrant set to false) , MultiLevelLock2.COMPATIBILITY_REENTRANTif lock level by the same owner shall not affect compatibility (same as reentrant set to true), or MultiLevelLock2.COMPATIBILITY_SUPPORTif lock levels that are the same as the desired shall not affect compatibility, or finally MultiLevelLock2.COMPATIBILITY_REENTRANT_AND_SUPPORTwhich is a combination of reentrant and support
    preferred - in case this lock request is incompatible with existing ones and we wait, it shall be granted before other waiting requests that are not preferred
    timeoutMSecs - if blocking is enabled by the wait parameter this specifies the maximum wait time in milliseconds
    
    Returns:
    true if the lock actually was acquired
    
    Throws:
    
    InterruptedException - when the thread waiting on this method is interrupted
    Since:
    
    1.1
    
    See Also:
    MultiLevelLock2.acquire(Object, int, boolean, int, boolean, long)
  - registerWaiter
```
protected void registerWaiter(GenericLock.LockOwner waitingOwner)
```
  - unregisterWaiter
```
protected void unregisterWaiter(GenericLock.LockOwner waitingOwner)
```
  - release
```
public boolean release(Object ownerId)
```
    Description copied from interface: MultiLevelLock
    
    Releases any lock levels the specified owner may hold on this lock.
    
    Specified by:
    
    release in interface MultiLevelLock
    
    Parameters:
    ownerId - a unique id identifying the entity that wants to release all lock levels
    
    Returns:
    true if the lock actually was released, false in case there was no lock held by the owner
    See Also:
    MultiLevelLock.release(Object)
  - getLockLevel
```
public int getLockLevel(Object ownerId)
```
    Description copied from interface: MultiLevelLock
    
    Retuns the highest lock level the specified owner holds on this lock or 0 if it holds no locks at all.
    
    Specified by:
    
    getLockLevel in interface MultiLevelLock
    
    Parameters:
    ownerId - a unique id identifying the entity that wants to know its highest lock level
    
    Returns:
    the highest lock level
    See Also:
    MultiLevelLock.getLockLevel(Object)
  - getResourceId
```
public Object getResourceId()
```
    Gets the resource assotiated to this lock.
    
    Returns:
    identifier for the resource associated to this lock
  - getLevelMinLock
```
public int getLevelMinLock()
```
    Gets the lowest lock level possible.
    
    Returns:
    minimum lock level
  - getLevelMaxLock
```
public int getLevelMaxLock()
```
    Gets the highst lock level possible.
    
    Returns:
    maximum lock level
  - getOwner
```
public Object getOwner()
```
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object
  - getMaxLevelOwner
```
protected GenericLock.LockOwner getMaxLevelOwner()
```
  - getMaxLevelOwner
```
protected GenericLock.LockOwner getMaxLevelOwner(GenericLock.LockOwner reentrantOwner,
                                     boolean preferred)
```
  - getMaxLevelOwner
```
protected GenericLock.LockOwner getMaxLevelOwner(int supportLockLevel,
                                     boolean preferred)
```
  - getMaxLevelOwner
```
protected GenericLock.LockOwner getMaxLevelOwner(GenericLock.LockOwner reentrantOwner,
                                     int supportLockLevel,
                                     boolean preferred)
```
  - setLockLevel
```
protected void setLockLevel(Object ownerId,
                GenericLock.LockOwner lock,
                int targetLockLevel,
                int compatibility,
                boolean intention)
```
  - tryLock
```
protected boolean tryLock(Object ownerId,
              int targetLockLevel,
              int compatibility,
              boolean preferred)
```
  - tryLock
```
protected boolean tryLock(Object ownerId,
              int targetLockLevel,
              int compatibility,
              boolean preferred,
              boolean tryOnly)
```
  - isCompatible
```
protected boolean isCompatible(int targetLockLevel,
                   int currentLockLevel)
```
  - getConflictingOwners
```
protected Set getConflictingOwners(Object ownerId,
                       int targetLockLevel,
                       int compatibility)
```
  - getConflictingWaiters
```
protected Collection getConflictingWaiters(Object ownerId)
```
  - getConflictingOwners
```
protected Set getConflictingOwners(GenericLock.LockOwner myOwner,
                       Collection ownersToTest)
```

	NO LOCK	SHARED	EXCLUSIVE
NO LOCK	o	o	o
SHARED	o	o	x
EXCLUSIVE	o	x	x

Class GenericLock

Nested Class Summary

Field Summary

Fields inherited from interface org.apache.commons.transaction.locking.MultiLevelLock2

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

resourceId

owners

waitingOwners

logger

waiters

Constructor Detail

GenericLock

Method Detail

equals

hashCode

test

has

acquire

acquire

acquire

acquire

registerWaiter

unregisterWaiter

release

getLockLevel

getResourceId

getLevelMinLock

getLevelMaxLock

getOwner

toString

getMaxLevelOwner

getMaxLevelOwner

getMaxLevelOwner

getMaxLevelOwner

setLockLevel

tryLock

tryLock

isCompatible

getConflictingOwners

getConflictingWaiters

getConflictingOwners