org.objectweb.cjdbc.common.util
Class ReadPrioritaryFIFOWriteLock

java.lang.Object
  org.objectweb.cjdbc.common.util.ReadPrioritaryFIFOWriteLock

public class ReadPrioritaryFIFOWriteLock

extends java.lang.Object

Reader/Writer lock with write priority.

If a reader holds the lock, all incoming readers are allowed to acquire the lock until a write arrives. A writer must wait for all current readers to release the lock before acquiring it.
When a writer has the lock, everybody else is blocked.
When a writer release the lock, there is a writer priority so if another writer is waiting it will have the lock even if it arrived later than readers. Writers are prioritary against readers but all writers get the lock in a FIFO order.

Version:

1.0

Author:

Emmanuel Cecchet

Field Summary

private int	activeReaders Threads executing read.
private boolean	activeWriter Is there an active writer?
private java.lang.Object	readSync
private int	waitingReaders Threads not yet in read.
private int	waitingWriters Threads not yet in write.
private java.util.ArrayList	writeWaitingQueue

Constructor Summary

ReadPrioritaryFIFOWriteLock()
Creates a new ReadPrioritaryFIFOWriteLock instance.

Method Summary

void	acquireRead() Acquires the lock for a read.
void	acquireWrite() Acquires the lock for a write.
boolean	isReadLocked() Tests if the lock is currently held by at least one reader.
boolean	isWriteLocked() Tests if the lock is currently held by a writer.
void	releaseRead() Releases a lock previously acquired for reading.
void	releaseWrite() Releases a lock previously acquired for writing.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

activeReaders

private int activeReaders

Threads executing read.

activeWriter

private boolean activeWriter

Is there an active writer?

waitingReaders

private int waitingReaders

Threads not yet in read.

waitingWriters

private int waitingWriters

Threads not yet in write.

readSync

private java.lang.Object readSync

writeWaitingQueue

private java.util.ArrayList writeWaitingQueue

Constructor Detail

ReadPrioritaryFIFOWriteLock

public ReadPrioritaryFIFOWriteLock()

Creates a new ReadPrioritaryFIFOWriteLock instance.

Method Detail

acquireRead

public void acquireRead()
                 throws java.lang.InterruptedException

Acquires the lock for a read.

Throws:

java.lang.InterruptedException - if wait failed (the lock should remain in a correct state)

releaseRead

public void releaseRead()

Releases a lock previously acquired for reading.

acquireWrite

public void acquireWrite()
                  throws java.lang.InterruptedException

Acquires the lock for a write.

Throws:

java.lang.InterruptedException - if wait failed (the lock should remain in a correct state)

releaseWrite

public void releaseWrite()

Releases a lock previously acquired for writing.

isReadLocked

public final boolean isReadLocked()

Tests if the lock is currently held by at least one reader.

Returns:

true if the lock is held by a reader

isWriteLocked

public final boolean isWriteLocked()

Tests if the lock is currently held by a writer.

Returns:

true if the lock is held by a writer