Standard placement operator

[Norman Feske]

Hello Sergey,

> My interest about STL containers has quite simple prerequisite. As far
> as I know Genode implementations of data structure (particularly,
> Avl_tree) has some issues and Genodelabs does not recommend it for usage
> in user applications. The reasons that issues are still not resolved is
> quite serious: Genode is kept as simple as possible. So, I was thinking

with the term "issue", are you referring to bugs and unexpected
behavior, or are you just finding those data structures limiting? If the
former is the case, I would be very grateful if you shared details about
the problems you encountered, so that we can remedy them.

The few data structures provided by Genode do merely exist to support
the operation of the base framework. By rigidly following the
microkernel construction principle, they comprise only those features
that cannot be left out. This is crucial for keeping the complexity of
the base system low. They should not be mistaken as an application
framework.

For components where low complexity and tight control over memory
allocations is critical (e.g., for resource multiplexers), I prefer to
stick with the sparse facilities provided by Genode's base API. In
contrast, for higher-level applications, the use of application-geared
APIs (such as STL, Qt and the like) seems more appropriate.

> about making a kind of porting of STL to Genode. But, it seems that this
> work is redundant since it is possible to use containers by means of
> specifying stdcxx in makefile. The only trouble is using Genode
> allocators/new operator instead of native C++ ones.

To integrate STL with Genode, you can define a new operator handing out
anonymous memory as follows:

  void *operator new (Genode::size_t size)
  {
    return Genode::env()->heap()->alloc(size);
  }

This operator will then be used by the standard C++ library and the STL
containers. By doing that, you are of course sacrificing the ability to
tightly guard allocations. For example, if your program is a server, it
will not be able to use distinct heap partitions to keep track of the
allocations performed on behalf of different clients. On the other hand,
many components do not need such strict accounting. The decision between
tight control (Genode API only) and convenience (Genode API + C++
standard library) is a trade-off and comes down to a judgment case by case.

Best regards
Norman

-- 
Dr.-Ing. Norman Feske
Genode Labs

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