New features in the GCC versions 4.3 and 4.4

Parallelization

All of the features mentioned thus far are available in version 4.3 of GCC, which is included by most distributions. The features that follow were added to the latest 4.4 version. The most important change here is improved multithreading support. The thread class from the thread library provides thread management methods.

Listing 2 shows how to start new threads and how a parent thread waits for a child thread to terminate.

Listing 2

Starting Threads

01 vector<thread *> active_threads(thread_num);
02 // Starte threads
03 for(unsigned int tn=0; tn<thread_num; tn++)
04 active_threads[tn] = new thread(worker,tn);
05 // Wait for child threads
06 for(unsigned int tn=0; tn<thread_num; tn++)
07 {
08 active_threads[tn]->join();
09 delete active_threads[tn];
10 }

The mutex library defines locking mechanisms. A simple example of the use of mutex is shown in Listing 3.

Listing 3

Example of mutex

01 mutex access_the_file; // Globale Variable
02 void a_function_that_runs_in_several_threads()
03 {
04 ...
05 access_the_file.lock();
06 // This area is not simultaneously accessible by multiple threads
07 ...
08 access_the_file.unlock();
09 ...
10 }

Additionally, support for the OpenMP parallel programming API is improved. The previous OpenMP specification required loop variables in a parallelized for loop to be of the int type. This restriction made it difficult to use OpenMP with STL containers. Version 3.0 of the OpenMP standard lifts this restriction; now, loops with STL iterators can be parallelized, as well as loops with int type loop variables, for example:

std::vector<int> vec(128);
#pragma omp parallel for default(none) shared(vec)
for (std::vector<int>::iterator it = vec.begin(); it < vec.end(); it++)
{
// work with iterator it
}

STL containers previously had the disadvantage of not supporting initialization in C array style, as in int a[] ={1,2,3}. The new C++ standard changes this, as in std::vector<int> a{1,2,3}; the inializer_list class is used to implement this new syntax.

Future

The development of the new C++ standard is not complete, and GCC is still catching up with some key new features of the standard. New regular expression components are not implemented in GCC 4.4.0; however, development is making rapid progress.

The part of the standard that governs atomic functions still seems to be under active development. Many function names were changed last year, and others were added.

Infos

  1. Boost C++ Libraries: http://www.boost.org
  2. "Working Draft, Standard for Programming Language C++": http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2857.pdf
  3. "Draft Technical Report on C++ Library Extensions": http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf

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