ReentrantWriterPreferenceReadWriteLock

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org.ematgine.utils.concurrent
Class ReentrantWriterPreferenceReadWriteLock

java.lang.Object
  org.ematgine.utils.concurrent.WriterPreferenceReadWriteLock
      org.ematgine.utils.concurrent.ReentrantWriterPreferenceReadWriteLock

All Implemented Interfaces:: ReadWriteLock

public class ReentrantWriterPreferenceReadWriteLock
extends WriterPreferenceReadWriteLock

A writer-preference ReadWriteLock that allows writers to reacquire read or write locks in the style of a ReentrantLock. Readers are not allowed until all write locks held by the writing thread have been released. Readers may also reacquire read locks, but not write locks. Among other applications, reentrancy can be useful when write locks are held during calls or callbacks to methods that perform reads under read locks.

Sample usage. Here is a code sketch showing how to exploit reentrancy to perform lock downgrading after updating a cache:

 class CachedData {
   Object data;
   volatile boolean cacheValid;
   ReentrantWriterPreferenceReadWriteLock rwl = ...

   void processCachedData() {
     rwl.readLock().acquire();
     if (!cacheValid) {

        // upgrade lock:
        rwl.readLock().release();   // must release first to obtain writelock
        rwl.writeLock().acquire();
        if (!cacheValid) { // recheck
          data = ...
          cacheValid = true;
        }
        // downgrade lock
        rwl.readLock().acquire();  // reacquire read without giving up lock
        rwl.writeLock().release(); // release write, still hold read
     }

     use(data);
     rwl.readLock().release();
   }
 }

[ Introduction to this package. ]

Nested Class Summary

Nested classes inherited from class org.ematgine.utils.concurrent.WriterPreferenceReadWriteLock

WriterPreferenceReadWriteLock.ReaderLock, WriterPreferenceReadWriteLock.Signaller, WriterPreferenceReadWriteLock.WriterLock

Field Summary

protected long writeHolds_
          Number of number of acquires on write lock by activeWriter_ thread

Fields inherited from class org.ematgine.utils.concurrent.WriterPreferenceReadWriteLock

activeReaders_, activeWriter_, readerLock_, waitingReaders_, waitingWriters_, writerLock_

Constructor Summary

ReentrantWriterPreferenceReadWriteLock()


Method Summary

protected boolean allowReader()
          Override this method to change to reader preference

protected WriterPreferenceReadWriteLock.Signaller endRead()
          Called upon termination of a read.

protected WriterPreferenceReadWriteLock.Signaller endWrite()
          Called upon termination of a write.

protected boolean startWrite()


Methods inherited from class org.ematgine.utils.concurrent.WriterPreferenceReadWriteLock

cancelledWaitingReader, cancelledWaitingWriter, readLock, startRead, startReadFromNewReader, startReadFromWaitingReader, startWriteFromNewWriter, startWriteFromWaitingWriter, writeLock

Methods inherited from class java.lang.Object

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

Field Detail

writeHolds_

protected long writeHolds_

Number of number of acquires on write lock by activeWriter_ thread

Constructor Detail