com.sun.identity.common

Class ReaderWriterLock

java.lang.Object

com.sun.identity.common.ReaderWriterLock

public class ReaderWriterLock
extends Object

This reader/writer lock prevents reads from occurring while writes are in progress, and it also prevents multiple writes from happening simultaneously. Multiple read operations can run in parallel, however. Reads take priority over writes, so any read operations that are pending while a write is in progress will execute before any subsequent writes execute. Writes are guaranteed to execute in the order in which they were requested -- the oldest request is processed first. You should use the lock as follows: public class Data_structure_or_resource { ReaderWriterLock lock = new ReaderWriterLock(); public void access() { try{ lock.readRequest(); // do the read/access operation here. }finally { lock.readDone(); } } public void modify( ) { try { lock.writeRequest(); // do the write/modify operation here. } finally { lock.writeDone(); } }

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ReaderWriterLock.Test The Test class is a unit test for the other code in the current file.

Constructor Summary

Constructors

Constructor and Description
ReaderWriterLock()

Method Summary

Modifier and Type	Method and Description
void	readDone() Release the lock.
void	readRequest() Request the read lock.
boolean	readRequestImmediate() This version of read() requests read access and returns true if you get it.
void	writeDone() Release the lock.
void	writeRequest() Request the write lock.
boolean	writeRequestImmediate() This version of the write request returns false immediately (without blocking) if any read or write operations are in progress and a write isn't safe; otherwise, it returns true and acquires the resource.

Methods inherited from class java.lang.Object

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

Constructor Detail

ReaderWriterLock

public ReaderWriterLock()

Method Detail

readRequest

public void readRequest()

Request the read lock. Block until a read operation can be performed safely. This call must be followed by a call to readDone() when the read operation completes.

readRequestImmediate

public boolean readRequestImmediate()

This version of read() requests read access and returns true if you get it. If it returns false, you may not safely read from the guarded resource. If it returns true, you should do the read, then call readDone in the normal way. Here's an example: public void read() { if( lock.readRequestImmediate() ) { try { // do the read operation here } finally { lock.readDone(); } }else { // couldn't read safely. }

readDone

public void readDone()

Release the lock. You must call this method when you're done with the read operation.

writeRequest

public void writeRequest()

Request the write lock. Block until a write operation can be performed safely. Write requests are guaranteed to be executed in the order received. Pending read requests take precedence over all write requests. This call must be followed by a call to writeDone() when the write operation completes.

writeRequestImmediate

public boolean writeRequestImmediate()

This version of the write request returns false immediately (without blocking) if any read or write operations are in progress and a write isn't safe; otherwise, it returns true and acquires the resource. Use it like this: public void write() { if( lock.writeRequestImmediate() ) { try { // do the write operation here } finally { lock.writeDone(); } }else { // couldn't write safely. } }

writeDone

public void writeDone()

Release the lock. You must call this method when you're done with the read operation.