- move Allocator abstract class to runtime namespace

- provide default implementation for allocator and deallocators

src/ngraph/runtime/allocator.cpp

+//*****************************************************************************
+// Copyright 2017-2019 Intel Corporation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//*****************************************************************************
+
+#include "ngraph/runtime/allocator.hpp"
+
+void* ngraph::runtime::Allocator::Malloc(void*, size_t size, size_t alignment)
+{
+    void* ptr = malloc(size);
+
+    // check for exception
+    if (size != 0 && !ptr)
+    {
+        throw ngraph_error("malloc failed to allocate memory of size " + std::to_string(size));
+        throw std::bad_alloc();
+    }
+    return ptr;
+}
+
+void ngraph::runtime::Allocator::Free(void* ptr, void*)
+{
+    if (ptr)
+    {
+        free(ptr);
+    }
+}

src/ngraph/runtime/allocator.hpp

+//*****************************************************************************
+// Copyright 2017-2019 Intel Corporation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//*****************************************************************************
+
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include "ngraph/except.hpp"
+#include "ngraph/util.hpp"
+
+namespace ngraph
+{
+    namespace runtime
+    {
+        class Allocator;
+    }
+}
+// Abstarct class for the allocator, for allocating and deallocating device memory
+class ngraph::runtime::Allocator
+{
+public:
+    virtual ~Allocator() = default;
+    virtual void* Malloc(void*, size_t size, size_t alignment);
+    virtual void Free(void* ptr, void*);
+};