ReentrantReadWriteLock

ReentrantReadWriteLock

java.util.concurrent.locks

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Java 5.0

serializable

This class implements the ReadWriteLock interface. The locks returned by the readLock( ) and writeLock( ) methods are instances of the inner classes ReadLock and WriteLock . ReentrantReadWriteLock defines a "fair mode" and includes instrumentation methods like ReentrantLock does.

Any number of threads can acquire the read lock as long as no thread holds or is attempting to acquire the write lock. When a thread attempts to acquire the write lock, no new read locks are granted. When all existing readers have relinquished the lock, the writer acquires the lock, and no reads are allowed until the writer has relinquished it. A thread that holds the write lock may downgrade to a read lock by acquiring the read lock and then relinquishing the write lock.

Because the read lock is not exclusive, it cannot have a Condition associated with it. The ReadLock.newCondition( ) method throws UnsupportedOperationException .

Figure 16-106. java.util.concurrent.locks.ReentrantReadWriteLock

 public class  ReentrantReadWriteLock  implements ReadWriteLock, Serializable {  // Public Constructors  public  ReentrantReadWriteLock  ( );        public  ReentrantReadWriteLock  (boolean  fair  );  // Nested Types  public static class  ReadLock  implements Lock, Serializable;       public static class  WriteLock  implements Lock, Serializable;  // Public Instance Methods  public final int  getQueueLength  ( );  default:0  public int  getReadLockCount  ( );  default:0  public int  getWaitQueueLength  (Condition  condition  );        public int  getWriteHoldCount  ( );  default:0  public final boolean  hasQueuedThread  (Thread  thread  );        public final boolean  hasQueuedThreads  ( );        public boolean  hasWaiters  (Condition  condition  );        public final boolean  isFair  ( );  default:false  public boolean  isWriteLocked  ( );  default:false  public boolean  isWriteLockedByCurrentThread  ( );  default:false  public ReentrantReadWriteLock.ReadLock  readLock  ( );        public ReentrantReadWriteLock.WriteLock  writeLock  ( );  // Public Methods Overriding Object  public String  toString  ( );  // Protected Instance Methods  protected Thread  getOwner  ( );        protected java.util.Collection<Thread>  getQueuedReaderThreads  ( );        protected java.util.Collection<Thread>  getQueuedThreads  ( );        protected java.util.Collection<Thread>  getQueuedWriterThreads  ( );        protected java.util.Collection<Thread>  getWaitingThreads  (Condition  condition  );   } 

Passed To

ReentrantReadWriteLock.ReadLock.ReadLock( ) , ReentrantReadWriteLock.WriteLock.WriteLock( )