Long live QSemaphoreReleaser!

This is a simple RAII class that makes semaphore releasing
reliable in the face of exceptions and early returns.

This code originates from KDTools' KDSemaphoreReleaser[1], but
has been extensively reworked to support C++11 move semantics.

[1] https://docs.kdab.com/kdtools/2.3.0/class_k_d_semaphore_releaser.html

[ChangeLog][QtCore][QSemaphore] Added a new RAII class, QSemaphoreReleaser,
to reliably perform release() calls.

Change-Id: I6aff64d37cc0882b17c4419817bde60b542f34d9
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: David Faure <david.faure@kdab.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/tests/auto/corelib/thread/qsemaphore/tst_qsemaphore.cpp b/tests/auto/corelib/thread/qsemaphore/tst_qsemaphore.cpp
index f1eb32a282..a33417c7da 100644
--- a/tests/auto/corelib/thread/qsemaphore/tst_qsemaphore.cpp
+++ b/tests/auto/corelib/thread/qsemaphore/tst_qsemaphore.cpp
@@ -42,6 +42,7 @@ private slots:
     void tryAcquireWithTimeout();
     void tryAcquireWithTimeoutStarvation();
     void producerConsumer();
+    void raii();
 };
 
 static QSemaphore *semaphore = 0;
@@ -415,5 +416,54 @@ void tst_QSemaphore::producerConsumer()
     consumer.wait();
 }
 
+void tst_QSemaphore::raii()
+{
+    QSemaphore sem;
+
+    QCOMPARE(sem.available(), 0);
+
+    // basic operation:
+    {
+        QSemaphoreReleaser r0;
+        const QSemaphoreReleaser r1(sem);
+        const QSemaphoreReleaser r2(sem, 2);
+
+        QCOMPARE(r0.semaphore(), nullptr);
+        QCOMPARE(r1.semaphore(), &sem);
+        QCOMPARE(r2.semaphore(), &sem);
+    }
+
+    QCOMPARE(sem.available(), 3);
+
+    // cancel:
+    {
+        const QSemaphoreReleaser r1(sem);
+        QSemaphoreReleaser r2(sem, 2);
+
+        QCOMPARE(r2.cancel(), &sem);
+        QCOMPARE(r2.semaphore(), nullptr);
+    }
+
+    QCOMPARE(sem.available(), 4);
+
+    // move-assignment:
+    {
+        const QSemaphoreReleaser r1(sem);
+        QSemaphoreReleaser r2(sem, 2);
+
+        QCOMPARE(sem.available(), 4);
+
+        r2 = QSemaphoreReleaser();
+
+        QCOMPARE(sem.available(), 6);
+
+        r2 = QSemaphoreReleaser(sem, 42);
+
+        QCOMPARE(sem.available(), 6);
+    }
+
+    QCOMPARE(sem.available(), 49);
+}
+
 QTEST_MAIN(tst_QSemaphore)
 #include "tst_qsemaphore.moc"