QSemaphore: add a note to update to noexcept in Qt 7

The QSemaphore acquire & release functions, plus the constructor and
destructor, can be made noexcept on platforms that use futexes
(currently, Linux and Windows; likely macOS by the time we make 7.0). I
didn't make the change right now because the acquire and release
functions have narrow contracts on the int n values. I didn't make that
change now because it make a mess of the code, for little gain as this
class isn't used that often.

Plus, we may want to investigate whether we want to keep the multi-token
semaphore functionality around (something neither POSIX sem_t nor
std::counting_semaphore have), or split that off into a separate class
like QBasicMutex / QMutex / QRecursiveMutex was done.

Change-Id: Ieab617d69f3b4b54ab30fffd175b27813728f2ce
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/corelib/thread/qsemaphore.cpp b/src/corelib/thread/qsemaphore.cpp
index af34a7bb39..a7b423e4e7 100644
--- a/src/corelib/thread/qsemaphore.cpp
+++ b/src/corelib/thread/qsemaphore.cpp
@@ -300,7 +300,12 @@ QSemaphore::~QSemaphore()
 */
 void QSemaphore::acquire(int n)
 {
+#if QT_VERSION >= QT_VERSION_CHECK(7, 0, 0)
+#  warning "Move the Q_ASSERT to inline code, make QSemaphore have wide contract, " \
+    "and mark noexcept where futexes are in use."
+#else
     Q_ASSERT_X(n >= 0, "QSemaphore::acquire", "parameter 'n' must be non-negative");
+#endif
 
     if (futexAvailable()) {
         futexSemaphoreTryAcquire(u, n, QDeadlineTimer::Forever);