FIFOReadWriteLock

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EDU.oswego.cs.dl.util.concurrent
Class FIFOReadWriteLock

java.lang.Object
  EDU.oswego.cs.dl.util.concurrent.FIFOReadWriteLock

All Implemented Interfaces:: ReadWriteLock

public class FIFOReadWriteLock
extends java.lang.Object
implements ReadWriteLock
extends java.lang.Object
implements ReadWriteLock

This class implements a policy for reader/writer locks in which threads contend in a First-in/First-out manner for access (modulo the limitations of FIFOSemaphore, which is used for queuing). This policy does not particularly favor readers or writers. As a byproduct of the FIFO policy, the attempt methods may return false even when the lock might logically be available, but, due to contention, cannot be accessed within the given time bound.

This lock is NOT reentrant. Current readers and writers should not try to re-obtain locks while holding them.

[ Introduction to this package. ]

See Also:: FIFOSemaphore

Nested Class Summary
`protected class`	`FIFOReadWriteLock.ReaderSync`
`protected class`	`FIFOReadWriteLock.WriterSync`

Field Summary
`protected FIFOSemaphore`	`entryLock` Fair Semaphore serving as a kind of mutual exclusion lock.
`protected int`	`exreaders` Number of threads that have exited read lock.
`protected int`	`readers` Number of threads that have entered read lock.
`protected Sync`	`readerSync`
`protected Sync`	`writerSync`

Constructor Summary
`FIFOReadWriteLock()`

Method Summary
`protected void`	`acquireRead()`
`protected void`	`acquireWrite()`
`protected boolean`	`attemptRead(long msecs)`
`protected boolean`	`attemptWrite(long msecs)`
`Sync`	`readLock()` get the readLock
`protected void`	`releaseRead()`
`protected void`	`releaseWrite()`
`Sync`	`writeLock()` get the writeLock

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

Field Detail

entryLock

protected final FIFOSemaphore entryLock

Fair Semaphore serving as a kind of mutual exclusion lock. Writers acquire on entry, and hold until rwlock exit. Readers acquire and release only during entry (but are blocked from doing so if there is an active writer).

readers

protected volatile int readers

Number of threads that have entered read lock. Note that this is never reset to zero. Incremented only during acquisition of read lock while the "entryLock" is held, but read elsewhere, so is declared volatile.

exreaders

protected int exreaders

Number of threads that have exited read lock. Note that this is never reset to zero. Accessed only in code protected by synchronized(this). When exreaders != readers, the rwlock is being used for reading. Else if the entry lock is held, it is being used for writing (or in transition). Else it is free. Note: To distinguish these states, we assume that fewer than 2^32 reader threads can simultaneously execute.

readerSync

protected final Sync readerSync

writerSync

protected final Sync writerSync

Constructor Detail