Examples of java.util.concurrent.locks.ReentrantReadWriteLock

java.util.concurrent.locks.ReentrantReadWriteLock
release read lock before acquiring write lock rwl.readLock().unlock(); rwl.writeLock().lock(); try { // Recheck state because another thread might have // acquired write lock and changed state before we did. if (!cacheValid) { data = ... cacheValid = true; } // Downgrade by acquiring read lock before releasing write lock rwl.readLock().lock(); } finally { rwl.writeLock().unlock(); // Unlock write, still hold read } } try { use(data); } finally { rwl.readLock().unlock(); } } }} ReentrantReadWriteLocks can be used to improve concurrency in some uses of some kinds of Collections. This is typically worthwhile only when the collections are expected to be large, accessed by more reader threads than writer threads, and entail operations with overhead that outweighs synchronization overhead. For example, here is a class using a TreeMap that is expected to be large and concurrently accessed.
```
  {@code}class RWDictionary  private final Map m = new TreeMap(); private final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock(); private final Lock r = rwl.readLock(); private final Lock w = rwl.writeLock(); public Data get(String key) { r.lock(); try { return m.get(key); } finally { r.unlock(); } } public String[] allKeys() { r.lock(); try { return m.keySet().toArray(); } finally { r.unlock(); } } public Data put(String key, Data value) { w.lock(); try { return m.put(key, value); } finally { w.unlock(); } } public void clear() { w.lock(); try { m.clear(); } finally { w.unlock(); } } }}
```
Implementation Notes

This lock supports a maximum of 65535 recursive write locks and 65535 read locks. Attempts to exceed these limits result in {@link Error} throws from locking methods. @since 1.5 @author Doug Lea

      lock.writeLock().lock();
   }


   public void testOneWriterMultipleReaders() throws InterruptedException
   {
      lock = new ReentrantReadWriteLock();


      Writer writer = new Writer("writer");
      Reader reader1 = new Reader("reader1");
      Reader reader2 = new Reader("reader2");

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      lockSegmentShift = 32 - tempLockSegShift;
      lockSegmentMask = numLocks - 1;


      sharedLocks = new ReentrantReadWriteLock[numLocks];


      for (int i = 0; i < numLocks; i++) sharedLocks[i] = new ReentrantReadWriteLock();
   }

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    * @param fqn       the Fqn to lock on
    * @param exclusive if true, a write (exclusive) lock is attempted, otherwise a read (shared) lock is used.
    */
   public void acquireLock(Fqn fqn, boolean exclusive)
   {
      ReentrantReadWriteLock lock = getLock(fqn);


      if (exclusive)
      {
         lock.writeLock().lock();
      }
      else
      {
         lock.readLock().lock();
      }
   }

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    *
    * @param fqn the Fqn to release
    */
   public void releaseLock(Fqn fqn)
   {
      ReentrantReadWriteLock lock = getLock(fqn);
      if (lock.isWriteLockedByCurrentThread())
      {
         lock.writeLock().unlock();
      }
      else
      {
         lock.readLock().unlock();
      }
   }

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   ReentrantReadWriteLock.WriteLock wl;


   @BeforeMethod(alwaysRun = true)
   public void setUp() throws Exception
   {
      lock = new ReentrantReadWriteLock();
      rl = lock.readLock();
      wl = lock.writeLock();
   }

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          + globalMaxAppAttempts + "]. Use the global max attempts instead.");
    } else {
      this.maxAppAttempts = individualMaxAppAttempts;
    }


    ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
    this.readLock = lock.readLock();
    this.writeLock = lock.writeLock();


    this.stateMachine = stateMachineFactory.make(this);
  }

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    this.eventHandler = rmContext.getDispatcher().getEventHandler();
    this.submissionContext = submissionContext;
    this.scheduler = scheduler;
    this.masterService = masterService;


    ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
    this.readLock = lock.readLock();
    this.writeLock = lock.writeLock();


    this.proxiedTrackingUrl = generateProxyUriWithoutScheme();
    
    this.stateMachine = stateMachineFactory.make(this);
    this.user = user;

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  DefaultServiceDiscovered(String name) {
    this.name = name;
    this.discoverables = new AtomicReference<Set<Discoverable>>(ImmutableSet.<Discoverable>of());
    this.listenerCallers = Lists.newLinkedList();
    this.callerLock = new ReentrantReadWriteLock();
  }

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{
    private final Lock readLock, writeLock;


    protected LockSupport()
    {
        ReentrantReadWriteLock lock = new ReentrantReadWriteLock();


        readLock = lock.readLock();
        writeLock = lock.writeLock();
    }

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   * byte[] objects and reduce heap usage.
   */
  private final NameCache<ByteArray> nameCache;


  FSDirectory(FSImage fsImage, FSNamesystem ns, Configuration conf) {
    this.dirLock = new ReentrantReadWriteLock(true); // fair
    this.cond = dirLock.writeLock().newCondition();
    rootDir = new INodeDirectoryWithQuota(INodeDirectory.ROOT_NAME,
        ns.createFsOwnerPermissions(new FsPermission((short)0755)),
        Integer.MAX_VALUE, UNKNOWN_DISK_SPACE);
    this.fsImage = fsImage;

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Examples of java.util.concurrent.locks.ReentrantReadWriteLock

Implementation Notes

Related Classes of java.util.concurrent.locks.ReentrantReadWriteLock