com.trolltech.qt.core
Class QReadWriteLock

java.lang.Object
  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.core.QReadWriteLock
All Implemented Interfaces:
QtJambiInterface

public class QReadWriteLock
extends QtJambiObject

The QReadWriteLock class provides read-write locking. A read-write lock is a synchronization tool for protecting resources that can be accessed for reading and writing. This type of lock is useful if you want to allow multiple threads to have simultaneous read-only access, but as soon as one thread wants to write to the resource, all other threads must be blocked until the writing is complete.

In many cases, QReadWriteLock is a direct competitor to QMutex. QReadWriteLock is a good choice if there are many concurrent reads and writing occurs infrequently.

Example:

        QReadWriteLock lock = new QReadWriteLock();

        public void readerFunction() {
            // ...
            lock.lockForRead();
            read_file();
            lock.unlock();
            // ...
        }

        public void writerFunction() {
            // ...
            lock.lockForWrite();
            write_file();
            lock.unlock();
            // ...
        }
To ensure that writers aren't blocked forever by readers, readers attempting to obtain a lock will not succeed if there is a blocked writer waiting for access, even if the lock is currently only accessed by other readers. Also, if the lock is accessed by a writer and another writer comes in, that writer will have priority over any readers that might also be waiting.

Like QMutex, a QReadWriteLock can be recursively locked by the same thread when constructed in QReadWriteLock::RecursionMode recursive mode}. In such cases, unlock() must be called the same number of times lockForWrite() or lockForRead() was called. Note that the lock type cannot be changed when trying to lock recursively, i.e. it is not possible to lock for reading in a thread that already has locked for writing (and vice versa).

See also:
QReadLocker, QWriteLocker, QMutex, and QSemaphore.


Nested Class Summary
static class QReadWriteLock.RecursionMode
          See also.
QReadWriteLock().
 
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9
 
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal
 
Field Summary
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
QReadWriteLock()
          Constructs a QReadWriteLock object in NonRecursive mode.
QReadWriteLock(QReadWriteLock.RecursionMode recursionMode)
          Constructs a QReadWriteLock object in the given recursionMode.
 
Method Summary
 void lockForRead()
          Locks the lock for reading.
 void lockForWrite()
          Locks the lock for writing.
 boolean tryLockForRead()
          Attempts to lock for reading.
 boolean tryLockForRead(int timeout)
          This is an overloaded member function, provided for convenience.
 boolean tryLockForWrite()
          Attempts to lock for writing.
 boolean tryLockForWrite(int timeout)
          This is an overloaded member function, provided for convenience.
 void unlock()
          Unlocks the lock.
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
__qt_signalInitialization
 
Methods inherited from class java.lang.Object
clone, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Constructor Detail

QReadWriteLock

public QReadWriteLock()
Constructs a QReadWriteLock object in NonRecursive mode.

See also:
lockForRead(), and lockForWrite().


QReadWriteLock

public QReadWriteLock(QReadWriteLock.RecursionMode recursionMode)
Constructs a QReadWriteLock object in the given recursionMode.

See also:
lockForRead(), lockForWrite(), and RecursionMode .

Method Detail

lockForRead

public final void lockForRead()
Locks the lock for reading. This function will block the current thread if any thread (including the current) has locked for writing.

See also:
unlock(), lockForWrite(), and tryLockForRead().


lockForWrite

public final void lockForWrite()
Locks the lock for writing. This function will block the current thread if another thread has locked for reading or writing.

See also:
unlock(), lockForRead(), and tryLockForWrite().


tryLockForRead

public final boolean tryLockForRead()
Attempts to lock for reading. If the lock was obtained, this function returns true, otherwise it returns false instead of waiting for the lock to become available, i.e. it does not block.

The lock attempt will fail if another thread has locked for writing.

If the lock was obtained, the lock must be unlocked with unlock() before another thread can successfully lock it.

See also:
unlock(), and lockForRead().


tryLockForRead

public final boolean tryLockForRead(int timeout)
This is an overloaded member function, provided for convenience.

Attempts to lock for reading. This function returns true if the lock was obtained; otherwise it returns false. If another thread has locked for writing, this function will wait for at most timeout milliseconds for the lock to become available.

Note: Passing a negative number as the timeout is equivalent to calling lockForRead(), i.e. this function will wait forever until lock can be locked for reading when timeout is negative.

If the lock was obtained, the lock must be unlocked with unlock() before another thread can successfully lock it.

See also:
unlock(), and lockForRead().


tryLockForWrite

public final boolean tryLockForWrite()
Attempts to lock for writing. If the lock was obtained, this function returns true; otherwise, it returns false immediately.

The lock attempt will fail if another thread has locked for reading or writing.

If the lock was obtained, the lock must be unlocked with unlock() before another thread can successfully lock it.

See also:
unlock(), and lockForWrite().


tryLockForWrite

public final boolean tryLockForWrite(int timeout)
This is an overloaded member function, provided for convenience.

Attempts to lock for writing. This function returns true if the lock was obtained; otherwise it returns false. If another thread has locked for reading or writing, this function will wait for at most timeout milliseconds for the lock to become available.

Note: Passing a negative number as the timeout is equivalent to calling lockForWrite(), i.e. this function will wait forever until lock can be locked for writing when timeout is negative.

If the lock was obtained, the lock must be unlocked with unlock() before another thread can successfully lock it.

See also:
unlock(), and lockForWrite().


unlock

public final void unlock()
Unlocks the lock.

Attempting to unlock a lock that is not locked is an error, and will result in program termination.

See also:
lockForRead(), lockForWrite(), tryLockForRead(), and tryLockForWrite().