QReadLocker Class | Qt Core 5.6

Qt 5.6 | Qt Core | C++ Classes | QReadLocker

Qt 5.6.2 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

- List of all members, including inherited members

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

## 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().