libcore: Locking a mutex without throwing exceptions

Most of the code has been written with the assumption that locking
a mutex will never throw an exception.

doomsday/libs/core/include/de/concurrency/lockable.h

@@ -39,9 +39,8 @@ class DENG2_PUBLIC Lockable
 {
 public:
     /// Acquire the lock.  Blocks until the operation succeeds.
-    inline void lock() const {
-        _mutex.lock();
-    }
+    /// @return @c true, if the lock succeeded. @c false, if there was an error.
+    bool lock() const noexcept;
 
     /// Release the lock.
     inline void unlock() const {

doomsday/libs/core/src/concurrency/lockable.cpp

@@ -23,6 +23,18 @@
 
 namespace de {
 
-// nothing here
+bool Lockable::lock() const noexcept
+{
+    try
+    {
+        _mutex.lock();
+        return true;
+    }
+    catch (...)
+    {
+        qWarning("[Lockable] (%p) Failed to lock mutex!", static_cast<void const *>(this));
+        return false;
+    }
+}
 
 } // namespace de