Feeds

Binary interfaces in component development

A template class with static data - how can that possibly go wrong?

Choosing a cloud hosting partner with confidence

As we know, with few exceptions, a C++ compiler instantiates a template whenever it is specialised, and the template definitions are available (see the ISO C++ standard paragraph 14.7.1). In our code, the template definitions are in the header file so the template definitions are always available. This means that each cpp file that uses the template will contain instantiated definitions of the static object in the compiled object file. When object files are linked, the linker notices that there are many definitions of a single symbol and it merges all definitions into a single definition. Such symbols are marked in the object file as “weak”, so that the linker will unify multiple definitions instead of complaining about a multiply-defined symbol. A counter example of a “strong” symbol is a non-inline function definition; here the linker would give an error if it came across a duplicate definition.

When these definitions all occur in a single monolithic binary, there are no problems. This is shown by the following example, where we introduce a singleton class that we implement via our GenericSingleton template. If the implementation works correctly then this object will be constructed and destructed only once. To test our singleton we add two further cpp files containing code that uses the resulting singleton, and a further cpp containing the main function. In our initial test, we run it as a monolithic binary and we expect that only a single singleton object will be constructed – see Figure 1.

Figure 1: Shows that everything is OK when we're building statically.

The above is the case where our binary is linked monolithically, using only static libraries and everything works. Now, imagine a scenario where your manager wants to decompose the project, so that different project teams can be responsible for their own dynamic library, so that development can occur in parallel, so that functionalities can be unit tested without rebuilding everything - and for all the other reasons that motivate people to use dynamic libraries. This manager, like lots of people, comes from a planet where an application can be built interchangeably, either statically or dynamically, with no difference in behaviour.

I’m sure we’d all like to come from this programmer’s paradise too, but until we can find a way to move there, maybe we’ll have to support our user base here on Earth with its less than perfect operating systems. So, what will happen when we take our simple program and change it from a monolithic binary into a set of dynamically-linked components?

Providing a secure and efficient Helpdesk

More from The Register

next story
Preview redux: Microsoft ships new Windows 10 build with 7,000 changes
Latest bleeding-edge bits borrow Action Center from Windows Phone
Google opens Inbox – email for people too thick to handle email
Print this article out and give it to someone tech-y if you get stuck
Microsoft promises Windows 10 will mean two-factor auth for all
Sneak peek at security features Redmond's baking into new OS
UNIX greybeards threaten Debian fork over systemd plan
'Veteran Unix Admins' fear desktop emphasis is betraying open source
Entity Framework goes 'code first' as Microsoft pulls visual design tool
Visual Studio database diagramming's out the window
Google+ goes TITSUP. But WHO knew? How long? Anyone ... Hello ...
Wobbly Gmail, Contacts, Calendar on the other hand ...
DEATH by PowerPoint: Microsoft warns of 0-day attack hidden in slides
Might put out patch in update, might chuck it out sooner
Redmond top man Satya Nadella: 'Microsoft LOVES Linux'
Open-source 'love' fairly runneth over at cloud event
prev story

Whitepapers

Choosing cloud Backup services
Demystify how you can address your data protection needs in your small- to medium-sized business and select the best online backup service to meet your needs.
Forging a new future with identity relationship management
Learn about ForgeRock's next generation IRM platform and how it is designed to empower CEOS's and enterprises to engage with consumers.
Security for virtualized datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.
Storage capacity and performance optimization at Mizuno USA
Mizuno USA turn to Tegile storage technology to solve both their SAN and backup issues.