Wrap default allocator in a unique pointer for automatic deallocation

src/ngraph/runtime/aligned_buffer.hpp

@@ -50,7 +50,11 @@ private:
     AlignedBuffer(const AlignedBuffer&) = delete;
     AlignedBuffer& operator=(const AlignedBuffer&) = delete;
 
+    // Allocator objects and the allocation interfaces are owned by the
+    // creators of AlignedBuffers. They need to ensure that the lifetime of
+    // m_allocator exceeds the lifetime of this AlignedBuffer.
     Allocator* m_allocator;
+
     char* m_allocated_buffer;
     char* m_aligned_buffer;
     size_t m_byte_size;

src/ngraph/runtime/allocator.cpp

@@ -51,6 +51,6 @@ public:
 
 ngraph::runtime::Allocator* ngraph::runtime::get_default_allocator()
 {
-    static DefaultAllocator* allocator = new DefaultAllocator();
-    return allocator;
+    static std::unique_ptr<DefaultAllocator> allocator(new DefaultAllocator());
+    return allocator.get();
 }

src/ngraph/runtime/allocator.hpp

@@ -28,8 +28,8 @@ namespace ngraph
     {
         class Allocator;
         class DefaultAllocator;
-        /// \brief Returns a statically allocated default ngraph allocator
-        //         that calls into system allocation libraries
+        /// \brief Returns a pointer to a statically allocated singleton
+        ///        allocator that calls into system allocation libraries
         Allocator* get_default_allocator();
     }
 }