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, 4 insertions, 4 deletions

diff --git a/src/corelib/thread/qmutex_p.h b/src/corelib/thread/qmutex_p.h
index 92f13b1b7d..3ef99d5fc0 100644
--- a/src/corelib/thread/qmutex_p.h
+++ b/src/corelib/thread/qmutex_p.h
@@ -86,7 +86,7 @@ public:
     QMutexPrivate();
 
     bool wait(int timeout = -1);
-    void wakeUp();
+    void wakeUp() Q_DECL_NOTHROW;
 
     // Conrol the lifetime of the privates
     QAtomicInt refCount;
@@ -115,7 +115,7 @@ public:
     QAtomicInt waiters; //number of thread waiting
     QAtomicInt possiblyUnlocked; //bool saying that a timed wait timed out
     enum { BigNumber = 0x100000 }; //Must be bigger than the possible number of waiters (number of threads)
-    void derefWaiters(int value);
+    void derefWaiters(int value) Q_DECL_NOTHROW;
 
     //platform specific stuff
 #if defined(Q_OS_MAC)
@@ -139,8 +139,8 @@ public:
     uint count;
     QMutex mutex;
 
-    bool lock(int timeout);
-    void unlock();
+    bool lock(int timeout) QT_MUTEX_LOCK_NOEXCEPT;
+    void unlock() Q_DECL_NOTHROW;
 };
 
 QT_END_NAMESPACE