QMutex Class

The QMutex class provides access serialization between threads. More…

Header	`#include <QMutex>`
CMake	`target_link_libraries(app PRIVATE Nt::Core)`
Module	Nt Core C++ Classes

List of all members, including inherited members

Public Functions

	QMutex()
void	lock()
void	unlock()
bool	tryLock(int timeoutMs = 0)
bool	tryLock(QDeadlineTimer deadline)
bool	try_lock_for(std::chrono::duration<Rep, Period> duration)
bool	try_lock_until(std::chrono::time_point<Clock, Duration> timePoint)
bool	try_lock()
bool	isRecursive() const

Detailed Description

A QMutex protects data that several threads access. A thread calls lock() before touching the data and unlock() afterwards; any other thread that calls lock() in the meantime blocks until the mutex is released. Prefer QMutexLocker, which unlocks the mutex automatically when it goes out of scope:

QMutex mutex;
int counter = 0;

void increment()
{
    QMutexLocker locker(&mutex);
    ++counter;
}

A QMutex is not recursive: locking it twice from the same thread without unlocking in between is undefined behavior. Use QRecursiveMutex when that is needed.

Differences from Qt

QMutex wraps std::timed_mutex. It has no RecursionMode constructor argument.

Member Function Documentation

QMutex::QMutex()

Constructs an unlocked mutex.

bool QMutex::isRecursive() const

Returns false; a QMutex is never recursive.

See also QRecursiveMutex.

void QMutex::lock()

Locks the mutex. If another thread holds the lock, this call blocks until the mutex becomes available.

See also unlock() and tryLock().

bool QMutex::try_lock()

Attempts to lock the mutex without blocking. Returns true if the lock was obtained; otherwise returns false. This is provided for use with std::lock and std::unique_lock.

See also tryLock().

template <class Rep, class Period>bool QMutex::try_lock_for(std::chrono::duration<Rep, Period> duration)

Attempts to lock the mutex, waiting for at most duration. Returns true if the lock was obtained; otherwise returns false. This is provided for use with std::unique_lock.

See also tryLock().

template <class Clock, class Duration>bool QMutex::try_lock_until(std::chrono::time_point<Clock, Duration> timePoint)

Attempts to lock the mutex, waiting until timePoint at most. Returns true if the lock was obtained; otherwise returns false. This is provided for use with std::unique_lock.

See also tryLock().

bool QMutex::tryLock(int timeoutMs = 0)

Attempts to lock the mutex, waiting up to timeoutMs milliseconds for it to become available. Returns true if the lock was obtained; otherwise returns false.

If timeoutMs is 0, the call returns immediately. A negative timeoutMs waits until the lock is obtained, like lock().

See also lock() and unlock().

bool QMutex::tryLock(QDeadlineTimer deadline)

This is an overloaded function.

Attempts to lock the mutex until deadline expires. Returns true if the lock was obtained; otherwise returns false. A deadline that never expires waits like lock().

This function was introduced in 6.6.

void QMutex::unlock()

Unlocks the mutex. The mutex must be locked by the calling thread.

See also lock().