- Qt 5.15
- Qt Core
- C++ Classes
- QWriteLocker
- Qt 5.15.18 Reference Documentation

# QWriteLocker Class

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

Header: | #include <QWriteLocker>
qmake: | QT += core

- List of all members, including inherited members

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

## Public Functions

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

## Detailed Description

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().