Mark mutex locking and unlocking functions with noexcept

Unlocking a mutex can never throw an exception. That doesn't make
sense and our code should make sure it can't happen. Right now,
provided that the system-level functions don't throw, we don't either.

Locking a mutex cannot throw on Linux because we use futexes
directly. A non-recursive mutex is just a futex, whereas a recursive
mutex uses a mutex (a futex) to manage a lock count.

However, on other platforms, due to the freelist, there can be memory
allocation, which means it might throw std::bad_alloc. Not because of
the freelist itself (that uses malloc and will just crash if malloc
fails) but because of Q_GLOBAL_STATIC. In 5.1, the global static will
be noexcept provided the type's constructor is so too (it is, in this
case).

Change-Id: I4c562383f48de1be7827b9afb512d73eaf0792d5
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/corelib/thread/qmutex_linux.cpp b/src/corelib/thread/qmutex_linux.cpp
index a10bd35eff..3ccaeff4e3 100644
--- a/src/corelib/thread/qmutex_linux.cpp
+++ b/src/corelib/thread/qmutex_linux.cpp
@@ -87,7 +87,7 @@ static inline int futexFlags()
     return value;
 }
 
-static inline int _q_futex(void *addr, int op, int val, const struct timespec *timeout)
+static inline int _q_futex(void *addr, int op, int val, const struct timespec *timeout) Q_DECL_NOTHROW
 {
     volatile int *int_addr = reinterpret_cast<volatile int *>(addr);
 #if Q_BYTE_ORDER == Q_BIG_ENDIAN && QT_POINTER_SIZE == 8
@@ -106,7 +106,7 @@ static inline QMutexData *dummyFutexValue()
     return reinterpret_cast<QMutexData *>(quintptr(3));
 }
 
-bool QBasicMutex::lockInternal(int timeout)
+bool QBasicMutex::lockInternal(int timeout) Q_DECL_NOTHROW
 {
     QElapsedTimer elapsedTimer;
     if (timeout >= 1)
@@ -147,7 +147,7 @@ bool QBasicMutex::lockInternal(int timeout)
     return true;
 }
 
-void QBasicMutex::unlockInternal()
+void QBasicMutex::unlockInternal() Q_DECL_NOTHROW
 {
     QMutexData *d = d_ptr.load();
     Q_ASSERT(d); //we must be locked