QSemaphoreReleaser Class

https:// can be used wherever you would otherwise use QSemaphore::release(). Constructing a https:// defers the release() call on the semaphore until the https:// is destroyed (see http://).

You can use this to reliably release a semaphore to avoid dead-lock in the face of exceptions or early returns:

// ... do something that may throw or return early
sem.release();

If an early return is taken or an exception is thrown before the sem.release() call is reached, the semaphore is not released, possibly preventing the thread waiting in the corresponding sem.acquire() call from ever continuing execution.

When using RAII instead:

const QSemaphoreReleaser releaser(sem);
// ... do something that may throw or early return
// implicitly calls sem.release() here and at every other return in between

this can no longer happen, because the compiler will make sure that the https:// destructor is always called, and therefore the semaphore is always released.

https:// is move-enabled and can therefore be returned from functions to transfer responsibility for releasing a semaphore out of a function or a scope:

{ // some scope
    QSemaphoreReleaser releaser; // does nothing
    // ...
    if (someCondition) {
        releaser = QSemaphoreReleaser(sem);
        // ...
    }
    // ...
} // conditionally calls sem.release(), depending on someCondition

A https:// can be canceled by a call to cancel(). A canceled semaphore releaser will no longer call QSemaphore::release() in its destructor.

See Also▲

QSemaphoreReleaser::QSemaphoreReleaser()▲

[explicit] QSemaphoreReleaser::QSemaphoreReleaser(int &sem, int n = 1)▲

[default] QSemaphoreReleaser::QSemaphoreReleaser(int *sem, int n)▲

[default] QSemaphoreReleaser::QSemaphoreReleaser(QSemaphoreReleaser &&other)▲

[default] QSemaphoreReleaser::~QSemaphoreReleaser()▲

[default] int QSemaphoreReleaser::operator=(QSemaphoreReleaser &&)▲