- Qt 5.5
- Qt Core
- C++ Classes
- QReadLocker
- Qt 5.5.1 Reference Documentation

# QReadLocker Class

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

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

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

- List of all members, including inherited members

## Public Functions

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

## Detailed Description

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

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

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

    QReadWriteLock lock;

    QByteArray readData()
    {
        QReadLocker locker(&lock);
        ...
        return data;
    }

It is equivalent to the following code:

    QReadWriteLock lock;

    QByteArray readData()
    {
        lock.lockForRead();
        ...
        lock.unlock();
        return data;
    }

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

See also QWriteLocker and QReadWriteLock.

## Member Function Documentation

### QReadLocker::QReadLocker(QReadWriteLock * lock)

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

See also QReadWriteLock::lockForRead().

### QReadLocker::~QReadLocker()

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

See also QReadWriteLock::unlock().

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

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

### void QReadLocker::relock()

Relocks an unlocked lock.

See also unlock().

### void QReadLocker::unlock()

Unlocks the lock associated with this locker.

See also QReadWriteLock::unlock().