name : IlmThreadNamespace.h // // SPDX-License-Identifier: BSD-3-Clause // Copyright (c) Contributors to the OpenEXR Project. // #ifndef INCLUDED_ILMTHREADNAMESPACE_H #define INCLUDED_ILMTHREADNAMESPACE_H // // The purpose of this file is to make it possible to specify an // ILMTHREAD_INTERNAL_NAMESPACE as a preprocessor definition and have all of // the IlmThread symbols defined within that namespace rather than the // standard IlmThread namespace. Those symbols are made available to client // code through the ILMTHREAD_NAMESPACE in addition to the // ILMTHREAD_INTERNAL_NAMESPACE. // // To ensure source code compatibility, the ILMTHREAD_NAMESPACE defaults to // IlmThread and then "using namespace ILMTHREAD_INTERNAL_NAMESPACE;" brings // all of the declarations from the ILMTHREAD_INTERNAL_NAMESPACE into the // ILMTHREAD_NAMESPACE. This means that client code can continue to use // syntax like IlmThread::Thread, but at link time it will resolve to a // mangled symbol based on the ILMTHREAD_INTERNAL_NAMESPACE. // // As an example, if one needed to build against a newer version of IlmThread // and have it run alongside an older version in the same application, it is // now possible to use an internal namespace to prevent collisions between // the older versions of IlmThread symbols and the newer ones. To do this, // the following could be defined at build time: // // ILMTHREAD_INTERNAL_NAMESPACE = IlmThread_v2 // // This means that declarations inside IlmThread headers look like this // (after the preprocessor has done its work): // // namespace IlmThread_v2 { // ... // class declarations // ... // } // // namespace IlmThread { // using namespace IlmThread_v2; // } // // // Open Source version of this file pulls in the IlmThreadConfig.h file // for the configure time options. // #include "IlmThreadConfig.h" #ifndef ILMTHREAD_NAMESPACE #define ILMTHREAD_NAMESPACE IlmThread #endif #ifndef ILMTHREAD_INTERNAL_NAMESPACE #define ILMTHREAD_INTERNAL_NAMESPACE ILMTHREAD_NAMESPACE #endif // // We need to be sure that we import the internal namespace into the public one. // To do this, we use the small bit of code below which initially defines // ILMTHREAD_INTERNAL_NAMESPACE (so it can be referenced) and then defines // ILMTHREAD_NAMESPACE and pulls the internal symbols into the public // namespace. // namespace ILMTHREAD_INTERNAL_NAMESPACE {} namespace ILMTHREAD_NAMESPACE { using namespace ILMTHREAD_INTERNAL_NAMESPACE; } // // There are identical pairs of HEADER/SOURCE ENTER/EXIT macros so that // future extension to the namespace mechanism is possible without changing // project source code. // #define ILMTHREAD_INTERNAL_NAMESPACE_HEADER_ENTER namespace ILMTHREAD_INTERNAL_NAMESPACE { #define ILMTHREAD_INTERNAL_NAMESPACE_HEADER_EXIT } #define ILMTHREAD_INTERNAL_NAMESPACE_SOURCE_ENTER namespace ILMTHREAD_INTERNAL_NAMESPACE { #define ILMTHREAD_INTERNAL_NAMESPACE_SOURCE_EXIT } #endif // INCLUDED_ILMTHREADNAMESPACE_H