Qt Reference Documentation

- Qt 4.8
- ALL VERSIONS

- A
- A
- A
- Print

# QWriteLocker Class Reference

The QWriteLocker class is a convenience class that simplifies locking and unlocking read-write locks for write access. More...

     #include <QWriteLocker>

Note: All functions in this class are thread-safe.

- List of all members, including inherited members

## Public Functions

| QWriteLocker ( QReadWriteLock * lock )
| ~QWriteLocker ()
QReadWriteLock * | readWriteLock () const
void | relock ()
void | unlock ()

## Detailed Description

The QWriteLocker class is a convenience class that simplifies locking and unlocking read-write locks for write access.

The purpose of QWriteLocker (and QReadLocker is to simplify QReadWriteLock locking and unlocking. Locking and unlocking statements or in exception handling code is error-prone and difficult to debug. QWriteLocker can be used in such situations to ensure that the state of the lock is always well-defined.

Here's an example that uses QWriteLocker to lock and unlock a read-write lock for writing:

     QReadWriteLock lock;

     void writeData(const QByteArray &data)
     {
         QWriteLocker locker(&lock);
         ...
     }

It is equivalent to the following code:

     QReadWriteLock lock;

     void writeData(const QByteArray &data)
     {
         lock.lockForWrite();
         ...
         lock.unlock();
     }

The QMutexLocker documentation shows examples where the use of a locker object greatly simplifies programming.

See also QReadLocker and QReadWriteLock.

## Member Function Documentation

### QWriteLocker::QWriteLocker ( QReadWriteLock * lock )

Constructs a QWriteLocker and locks lock for writing. The lock will be unlocked when the QWriteLocker is destroyed. If `lock` is zero, QWriteLocker does nothing.

See also QReadWriteLock::lockForWrite().

### QWriteLocker::~QWriteLocker ()

Destroys the QWriteLocker and unlocks the lock that was passed to the constructor.

See also QReadWriteLock::unlock().

### QReadWriteLock * QWriteLocker::readWriteLock () const

Returns a pointer to the read-write lock that was passed to the constructor.

### void QWriteLocker::relock ()

Relocks an unlocked lock.

See also unlock().

### void QWriteLocker::unlock ()

Unlocks the lock associated with this locker.

See also QReadWriteLock::unlock().